Merge pull request #124 from docker/feat-generate-vsa-policy-uri

feat: add `digest` and `downloadLocation` to VSA policy

README.md

@@ -345,7 +345,11 @@ The VSA can be signed and published to the registry using the signing functions
     "timeVerified": "2024-04-19T08:00:00.01Z",
     "resourceUri": "pkg:docker/example.org/example-image@1.0?platform=linux%2Famd64&digest=sha256%3A49f717386e5462e945232569a97a05831cb83bef8c3369be3bb7ea1793686960",
     "policy": {
-      "uri": "https://example.org/internal-policy/v1"
+      "uri": "https://example.org/internal-policy/v1",
+      "downloadLocation": "https://docker.github.io/tuf-staging/targets/docker/d71d6b8f49fcba1295b16f5394dd5863a14e4277eb663d66d8c48e392509afe0.policy.rego",
+      "digest": {
+        "sha256": "d71d6b8f49fcba1295b16f5394dd5863a14e4277eb663d66d8c48e392509afe0"
+      }
     },
     "verificationResult": "PASSED",
     "verifiedLevels": ["SLSA_BUILD_LEVEL_3"]

internal/test/test.go

@@ -2,22 +2,13 @@ package test
 
 import (
 	"context"
-	"encoding/base64"
-	"encoding/json"
-	"fmt"
 	"os"
 	"path/filepath"
-	"strings"
 	"testing"
 
-	"github.com/docker/attest/pkg/attestation"
 	"github.com/docker/attest/pkg/policy"
 	"github.com/docker/attest/pkg/signerverifier"
 	"github.com/docker/attest/pkg/tlog"
-	v1 "github.com/google/go-containerregistry/pkg/v1"
-	"github.com/google/go-containerregistry/pkg/v1/layout"
-	"github.com/google/go-containerregistry/pkg/v1/partial"
-	intoto "github.com/in-toto/in-toto-golang/in_toto"
 	"github.com/secure-systems-lab/go-securesystemslib/dsse"
 )
 
@@ -30,6 +21,8 @@ const (
 	AWSKMSKeyARN = "arn:aws:kms:us-east-1:175142243308:alias/doi-signing" // sandbox
 )
 
+var UnsignedTestImage = filepath.Join("..", "..", "test", "testdata", "unsigned-test-image")
+
 func CreateTempDir(t *testing.T, dir, pattern string) string {
 	// Create a temporary directory for output oci layout
 	tempDir, err := os.MkdirTemp(dir, pattern)
@@ -89,108 +82,3 @@ func Setup(t *testing.T) (context.Context, dsse.SignerVerifier) {
 
 	return ctx, signer
 }
-
-type AnnotatedStatement struct {
-	OCIDescriptor   *v1.Descriptor
-	InTotoStatement *intoto.Statement
-	Annotations     map[string]string
-}
-
-func ExtractStatementsFromIndex(idx v1.ImageIndex, mediaType string) ([]*AnnotatedStatement, error) {
-	mfs2, err := idx.IndexManifest()
-	if err != nil {
-		return nil, fmt.Errorf("failed to extract IndexManifest from ImageIndex: %w", err)
-	}
-
-	var statements []*AnnotatedStatement
-
-	for i := range mfs2.Manifests {
-		mf := &mfs2.Manifests[i]
-		if mf.Annotations[attestation.DockerReferenceType] != "attestation-manifest" {
-			continue
-		}
-
-		attestationImage, err := idx.Image(mf.Digest)
-		if err != nil {
-			return nil, fmt.Errorf("failed to extract attestation image with digest %s: %w", mf.Digest.String(), err)
-		}
-		layers, err := attestationImage.Layers()
-		if err != nil {
-			return nil, fmt.Errorf("failed to extract layers from attestation image: %w", err)
-		}
-
-		for _, layer := range layers {
-			// parse layer blob as json
-			mt, err := layer.MediaType()
-			if err != nil {
-				return nil, fmt.Errorf("failed to get layer media type: %w", err)
-			}
-
-			if string(mt) != mediaType {
-				continue
-			}
-			r, err := layer.Uncompressed()
-			if err != nil {
-				return nil, fmt.Errorf("failed to get layer contents: %w", err)
-			}
-			defer r.Close()
-			inTotoStatement := new(intoto.Statement)
-			var desc *v1.Descriptor
-			if strings.HasSuffix(string(mt), "+dsse") {
-				env := new(attestation.Envelope)
-				err = json.NewDecoder(r).Decode(env)
-				if err != nil {
-					return nil, fmt.Errorf("failed to decode env: %w", err)
-				}
-				payload, err := base64.StdEncoding.Strict().DecodeString(env.Payload)
-				if err != nil {
-					return nil, fmt.Errorf("failed to decode payload: %w", err)
-				}
-				err = json.Unmarshal([]byte(payload), inTotoStatement)
-				if err != nil {
-					return nil, fmt.Errorf("failed to decode %s statement: %w", mediaType, err)
-				}
-			} else {
-				desc := new(v1.Descriptor)
-				err = json.NewDecoder(r).Decode(desc)
-				if err != nil {
-					return nil, fmt.Errorf("failed to decode statement: %w", err)
-				}
-			}
-
-			layerDesc, err := partial.Descriptor(layer)
-			if err != nil {
-				return nil, fmt.Errorf("failed to get descriptor for layer: %w", err)
-			}
-			annotations := make(map[string]string)
-			for k, v := range layerDesc.Annotations {
-				annotations[k] = v
-			}
-			statements = append(statements, &AnnotatedStatement{
-				OCIDescriptor:   desc,
-				InTotoStatement: inTotoStatement,
-				Annotations:     annotations,
-			})
-		}
-	}
-	return statements, nil
-}
-
-func ExtractAnnotatedStatements(path string, mediaType string) ([]*AnnotatedStatement, error) {
-	idx, err := layout.ImageIndexFromPath(path)
-	if err != nil {
-		return nil, fmt.Errorf("failed to load image index: %w", err)
-	}
-
-	idxm, err := idx.IndexManifest()
-	if err != nil {
-		return nil, fmt.Errorf("failed to get digest: %w", err)
-	}
-	idxDigest := idxm.Manifests[0].Digest
-
-	mfs, err := idx.ImageIndex(idxDigest)
-	if err != nil {
-		return nil, fmt.Errorf("failed to extract ImageIndex for digest %s: %w", idxDigest.String(), err)
-	}
-	return ExtractStatementsFromIndex(mfs, mediaType)
-}

pkg/attest/README.md

@@ -0,0 +1,2 @@
+## attest
+This package implements the top-level signing and verification methods.

pkg/attest/sign.go

@@ -12,14 +12,14 @@ import (
 // this is only relevant if there are (unsigned) in-toto statements.
 func SignStatements(ctx context.Context, idx v1.ImageIndex, signer dsse.SignerVerifier, opts *attestation.SigningOptions) ([]*attestation.Manifest, error) {
 	// extract attestation manifests from index
-	attestationManifests, err := attestation.GetAttestationManifestsFromIndex(idx)
+	attestationManifests, err := attestation.ManifestsFromIndex(idx)
 	if err != nil {
 		return nil, fmt.Errorf("failed to load attestation manifests from index: %w", err)
 	}
 	// sign every attestation layer in each manifest
 	for _, manifest := range attestationManifests {
 		for _, layer := range manifest.OriginalLayers {
-			err = manifest.AddAttestation(ctx, signer, layer.Statement, opts)
+			err = manifest.Add(ctx, signer, layer.Statement, opts)
 			if err != nil {
 				return nil, fmt.Errorf("failed to sign attestation layer %w", err)
 			}

pkg/attest/sign_test.go

@@ -1,10 +1,6 @@
 package attest
 
 import (
-	"encoding/json"
-	"fmt"
-	"net/http/httptest"
-	"net/url"
 	"path/filepath"
 	"testing"
 
@@ -12,10 +8,6 @@ import (
 	"github.com/docker/attest/pkg/attestation"
 	"github.com/docker/attest/pkg/oci"
 	"github.com/docker/attest/pkg/policy"
-	"github.com/google/go-containerregistry/pkg/registry"
-	v1 "github.com/google/go-containerregistry/pkg/v1"
-	"github.com/google/go-containerregistry/pkg/v1/static"
-	"github.com/google/go-containerregistry/pkg/v1/types"
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
 	v02 "github.com/in-toto/in-toto-golang/in_toto/slsa_provenance/v0.2"
 	"github.com/stretchr/testify/assert"
@@ -23,7 +15,6 @@ import (
 )
 
 var (
-	UnsignedTestImage   = filepath.Join("..", "..", "test", "testdata", "unsigned-test-image")
 	NoProvenanceImage   = filepath.Join("..", "..", "test", "testdata", "no-provenance-image")
 	PassPolicyDir       = filepath.Join("..", "..", "test", "testdata", "local-policy-pass")
 	PassMirrorPolicyDir = filepath.Join("..", "..", "test", "testdata", "local-policy-mirror")
@@ -42,8 +33,8 @@ func TestSignVerifyOCILayout(t *testing.T) {
 		expectedAttestations int
 		replace              bool
 	}{
-		{"signed replaced", UnsignedTestImage, 0, 4, true},
-		{"without replace", UnsignedTestImage, 4, 4, false},
+		{"signed replaced", test.UnsignedTestImage, 0, 4, true},
+		{"without replace", test.UnsignedTestImage, 4, 4, false},
 		// image without provenance doesn't fail
 		{"no provenance (replace)", NoProvenanceImage, 0, 2, true},
 		{"no provenance (no replace)", NoProvenanceImage, 2, 2, false},
@@ -70,10 +61,10 @@ func TestSignVerifyOCILayout(t *testing.T) {
 			require.NoError(t, err)
 			assert.Equalf(t, OutcomeSuccess, policy.Outcome, "Policy should have been found")
 
-			var allEnvelopes []*test.AnnotatedStatement
+			var allEnvelopes []*attestation.AnnotatedStatement
 			for _, predicate := range []string{intoto.PredicateSPDX, v02.PredicateSLSAProvenance, attestation.VSAPredicateType} {
 				mt, _ := attestation.DSSEMediaType(predicate)
-				statements, err := test.ExtractAnnotatedStatements(outputLayout, mt)
+				statements, err := attestation.ExtractAnnotatedStatements(outputLayout, mt)
 				require.NoError(t, err)
 				allEnvelopes = append(allEnvelopes, statements...)
 
@@ -83,150 +74,9 @@ func TestSignVerifyOCILayout(t *testing.T) {
 				}
 			}
 			assert.Equalf(t, tc.expectedAttestations, len(allEnvelopes), "expected %d attestations, got %d", tc.expectedAttestations, len(allEnvelopes))
-			statements, err := test.ExtractAnnotatedStatements(outputLayout, intoto.PayloadType)
+			statements, err := attestation.ExtractAnnotatedStatements(outputLayout, intoto.PayloadType)
 			require.NoError(t, err)
 			assert.Equalf(t, tc.expectedStatements, len(statements), "expected %d statement, got %d", tc.expectedStatements, len(statements))
 		})
 	}
 }
-
-func TestAddSignedLayerAnnotations(t *testing.T) {
-	ctx, signer := test.Setup(t)
-	testCases := []struct {
-		name    string
-		replace bool
-	}{
-		{"replaced", true},
-		{"not replaced", false},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			data := []byte("signed")
-			testLayer := static.NewLayer(data, types.MediaType(intoto.PayloadType))
-			mediaType := types.OCIManifestSchema1
-			opts := &attestation.SigningOptions{}
-			originalLayer := &attestation.Layer{
-				Layer: testLayer,
-				Statement: &intoto.Statement{
-					StatementHeader: intoto.StatementHeader{
-						PredicateType: attestation.VSAPredicateType,
-					},
-				},
-				Annotations: map[string]string{"test": "test"},
-			}
-
-			manifest := &attestation.Manifest{
-				OriginalDescriptor: &v1.Descriptor{
-					MediaType: mediaType,
-				},
-				OriginalLayers: []*attestation.Layer{
-					originalLayer,
-				},
-				SubjectDescriptor: &v1.Descriptor{},
-			}
-			err := manifest.AddAttestation(ctx, signer, originalLayer.Statement, opts)
-			require.NoError(t, err)
-
-			newImg, err := manifest.BuildAttestationImage(attestation.WithReplacedLayers(tc.replace))
-			require.NoError(t, err)
-			mf, _ := newImg.RawManifest()
-			type Annotations struct {
-				Annotations map[string]string `json:"annotations"`
-			}
-			type Layers struct {
-				Layers []Annotations `json:"layers"`
-			}
-			l := &Layers{}
-			err = json.Unmarshal(mf, l)
-			require.NoError(t, err)
-			_, ok := l.Layers[0].Annotations["test"]
-			assert.Truef(t, ok, "missing annotations")
-		})
-	}
-}
-
-func TestSimpleStatementSigning(t *testing.T) {
-	ctx, signer := test.Setup(t)
-	empty := types.MediaType("application/vnd.oci.empty.v1+json")
-	testCases := []struct {
-		name    string
-		replace bool
-	}{
-		{"replaced", true},
-		{"not replaced", false},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			opts := &attestation.SigningOptions{}
-			statement := &intoto.Statement{
-				StatementHeader: intoto.StatementHeader{
-					PredicateType: attestation.VSAPredicateType,
-				},
-			}
-			statement2 := &intoto.Statement{
-				StatementHeader: intoto.StatementHeader{
-					PredicateType: attestation.VSAPredicateType,
-				},
-			}
-			digest, err := v1.NewHash("sha256:da8b190665956ea07890a0273e2a9c96bfe291662f08e2860e868eef69c34620")
-			require.NoError(t, err)
-			subject := &v1.Descriptor{
-				MediaType: "application/vnd.oci.image.manifest.v1+json",
-				Digest:    digest,
-			}
-			manifest, err := NewAttestationManifest(subject)
-			require.NoError(t, err)
-			err = manifest.AddAttestation(ctx, signer, statement, opts)
-			require.NoError(t, err)
-
-			err = manifest.AddAttestation(ctx, signer, statement2, opts)
-			require.NoError(t, err)
-
-			// fake that the manfifest was loaded from a real image
-			manifest.OriginalLayers = manifest.SignedLayers
-			envelopes, err := oci.ExtractEnvelopes(manifest, attestation.VSAPredicateType)
-			require.NoError(t, err)
-			assert.Len(t, envelopes, 2)
-
-			newImg, err := manifest.BuildAttestationImage(attestation.WithReplacedLayers(tc.replace))
-			require.NoError(t, err)
-			layers, err := newImg.Layers()
-			require.NoError(t, err)
-			if tc.replace {
-				assert.Len(t, layers, 2)
-			} else {
-				assert.Len(t, layers, 4)
-			}
-
-			newImgs, err := manifest.BuildReferringArtifacts()
-			require.NoError(t, err)
-			assert.Len(t, newImgs, 2)
-			for _, img := range newImgs {
-				mf, err := img.Manifest()
-				require.NoError(t, err)
-				assert.Contains(t, mf.ArtifactType, "application/vnd.in-toto")
-				assert.Contains(t, mf.ArtifactType, "+dsse")
-				assert.Equal(t, subject.MediaType, mf.MediaType)
-				assert.Equal(t, empty, mf.Config.MediaType)
-				assert.Equal(t, int64(2), mf.Config.Size)
-				assert.Equal(t, "{}", string(mf.Config.Data))
-				layers, err := img.Layers()
-				require.NoError(t, err)
-				assert.Len(t, layers, 1)
-			}
-			server := httptest.NewServer(registry.New(registry.WithReferrersSupport(true)))
-			defer server.Close()
-
-			u, err := url.Parse(server.URL)
-			require.NoError(t, err)
-
-			indexName := fmt.Sprintf("%s/repo:root", u.Host)
-			output, err := oci.ParseImageSpecs(indexName)
-			require.NoError(t, err)
-			err = oci.SaveReferrers(manifest, output)
-			require.NoError(t, err)
-		})
-	}
-}

pkg/attest/verify.go

@@ -11,7 +11,6 @@ import (
 	"github.com/docker/attest/pkg/config"
 	"github.com/docker/attest/pkg/oci"
 	"github.com/docker/attest/pkg/policy"
-	v1 "github.com/google/go-containerregistry/pkg/v1"
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
 )
 
@@ -87,6 +86,8 @@ func toVerificationResult(p *policy.Policy, input *policy.Input, result *policy.
 		return nil, err
 	}
 
+	vsaPolicy := attestation.VSAPolicy{URI: result.Summary.PolicyURI, DownloadLocation: p.URI, Digest: p.Digest}
+
 	return &VerificationResult{
 		Policy:     p,
 		Outcome:    outcome,
@@ -104,7 +105,7 @@ func toVerificationResult(p *policy.Policy, input *policy.Input, result *policy.
 				},
 				TimeVerified:       time.Now().UTC().Format(time.RFC3339),
 				ResourceURI:        resourceURI,
-				Policy:             attestation.VSAPolicy{URI: result.Summary.PolicyURI},
+				Policy:             vsaPolicy,
 				VerificationResult: outcomeStr,
 				VerifiedLevels:     result.Summary.SLSALevels,
 			},
@@ -112,7 +113,7 @@ func toVerificationResult(p *policy.Policy, input *policy.Input, result *policy.
 	}, nil
 }
 
-func VerifyAttestations(ctx context.Context, resolver oci.AttestationResolver, pctx *policy.Policy) (*VerificationResult, error) {
+func VerifyAttestations(ctx context.Context, resolver attestation.Resolver, pctx *policy.Policy) (*VerificationResult, error) {
 	desc, err := resolver.ImageDescriptor(ctx)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get image descriptor: %w", err)
@@ -164,13 +165,3 @@ func VerifyAttestations(ctx context.Context, resolver oci.AttestationResolver, p
 	verificationResult.SubjectDescriptor = desc
 	return verificationResult, nil
 }
-
-func NewAttestationManifest(subject *v1.Descriptor) (*attestation.Manifest, error) {
-	return &attestation.Manifest{
-		OriginalDescriptor: &v1.Descriptor{
-			MediaType: "application/vnd.oci.image.manifest.v1+json",
-		},
-		OriginalLayers:    []*attestation.Layer{},
-		SubjectDescriptor: subject,
-	}, nil
-}

pkg/attest/verify_test.go

@@ -31,7 +31,7 @@ func TestVerifyAttestations(t *testing.T) {
 	env := new(attestation.Envelope)
 	err = json.Unmarshal(ex, env)
 	assert.NoError(t, err)
-	resolver := &oci.MockResolver{
+	resolver := &attestation.MockResolver{
 		Envs: []*attestation.Envelope{env},
 	}
 
@@ -47,7 +47,7 @@ func TestVerifyAttestations(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			mockPE := policy.MockPolicyEvaluator{
-				EvaluateFunc: func(_ context.Context, _ oci.AttestationResolver, _ *policy.Policy, _ *policy.Input) (*policy.Result, error) {
+				EvaluateFunc: func(_ context.Context, _ attestation.Resolver, _ *policy.Policy, _ *policy.Input) (*policy.Result, error) {
 					return policy.AllowedResult(), tc.policyEvaluationError
 				},
 			}
@@ -72,7 +72,7 @@ func TestVSA(t *testing.T) {
 	outputLayout := test.CreateTempDir(t, "", TestTempDir)
 
 	opts := &attestation.SigningOptions{}
-	attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	assert.NoError(t, err)
 	signedManifests, err := SignStatements(ctx, attIdx.Index, signer, opts)
 	require.NoError(t, err)
@@ -112,7 +112,9 @@ func TestVSA(t *testing.T) {
 	assert.Equal(t, "PASSED", attestationPredicate.VerificationResult)
 	assert.Equal(t, "docker-official-images", attestationPredicate.Verifier.ID)
 	assert.Equal(t, []string{"SLSA_BUILD_LEVEL_3"}, attestationPredicate.VerifiedLevels)
+	assert.Equal(t, PassPolicyDir+"/policy.rego", attestationPredicate.Policy.DownloadLocation)
 	assert.Equal(t, "https://docker.com/official/policy/v0.1", attestationPredicate.Policy.URI)
+	assert.Equal(t, map[string]string{"sha256": "d71d6b8f49fcba1295b16f5394dd5863a14e4277eb663d66d8c48e392509afe0"}, attestationPredicate.Policy.Digest)
 }
 
 func TestVerificationFailure(t *testing.T) {
@@ -122,7 +124,7 @@ func TestVerificationFailure(t *testing.T) {
 	outputLayout := test.CreateTempDir(t, "", TestTempDir)
 
 	opts := &attestation.SigningOptions{}
-	attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	assert.NoError(t, err)
 	signedManifests, err := SignStatements(ctx, attIdx.Index, signer, opts)
 	require.NoError(t, err)
@@ -162,7 +164,9 @@ func TestVerificationFailure(t *testing.T) {
 	assert.Equal(t, "FAILED", attestationPredicate.VerificationResult)
 	assert.Equal(t, "docker-official-images", attestationPredicate.Verifier.ID)
 	assert.Equal(t, []string{"SLSA_BUILD_LEVEL_3"}, attestationPredicate.VerifiedLevels)
+	assert.Equal(t, FailPolicyDir+"/policy.rego", attestationPredicate.Policy.DownloadLocation)
 	assert.Equal(t, "https://docker.com/official/policy/v0.1", attestationPredicate.Policy.URI)
+	assert.Equal(t, map[string]string{"sha256": "ad045e1bd7cd602d90196acf68f2c57d7b51565d59e6e30e30d94ae86aa16201"}, attestationPredicate.Policy.Digest)
 }
 
 func TestSignVerify(t *testing.T) {
@@ -185,7 +189,7 @@ func TestSignVerify(t *testing.T) {
 		{name: "mirror no match", signTL: true, policyDir: PassMirrorPolicyDir, imageName: "incorrect.org/library/test-image:test", expectError: true},
 	}
 
-	attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	assert.NoError(t, err)
 
 	for _, tc := range testCases {

pkg/attestation/README.md

@@ -0,0 +1,4 @@
+## attestations
+This package is for components that deal with the creation, storage, and retrieval of signed attestions using OCI. 
+
+For more generic OCI components see the `oci` package.

pkg/attestation/attestation.go

@@ -1,14 +1,17 @@
 package attestation
 
 import (
-	"bytes"
 	"context"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"maps"
+	"strings"
 
+	"github.com/docker/attest/pkg/oci"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/empty"
+	"github.com/google/go-containerregistry/pkg/v1/layout"
 	"github.com/google/go-containerregistry/pkg/v1/match"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/partial"
@@ -18,8 +21,19 @@ import (
 	"github.com/secure-systems-lab/go-securesystemslib/dsse"
 )
 
-// GetAttestationManifestsFromIndex extracts all attestation manifests from an index.
-func GetAttestationManifestsFromIndex(index v1.ImageIndex) ([]*Manifest, error) {
+// NewManifest creates a new attestation manifest from a descriptor.
+func NewManifest(subject *v1.Descriptor) (*Manifest, error) {
+	return &Manifest{
+		OriginalDescriptor: &v1.Descriptor{
+			MediaType: "application/vnd.oci.image.manifest.v1+json",
+		},
+		OriginalLayers:    []*Layer{},
+		SubjectDescriptor: subject,
+	}, nil
+}
+
+// ManifestsFromIndex extracts all attestation manifests from an index.
+func ManifestsFromIndex(index v1.ImageIndex) ([]*Manifest, error) {
 	idx, err := index.IndexManifest()
 	if err != nil {
 		return nil, fmt.Errorf("failed to extract IndexManifest from ImageIndex: %w", err)
@@ -42,7 +56,7 @@ func GetAttestationManifestsFromIndex(index v1.ImageIndex) ([]*Manifest, error)
 			if err != nil {
 				return nil, fmt.Errorf("failed to extract attestation image with digest %s: %w", desc.Digest.String(), err)
 			}
-			attestationLayers, err := GetAttestationsFromImage(attestationImage)
+			attestationLayers, err := layersFromImage(attestationImage)
 			if err != nil {
 				return nil, fmt.Errorf("failed to get attestations from image: %w", err)
 			}
@@ -57,8 +71,8 @@ func GetAttestationManifestsFromIndex(index v1.ImageIndex) ([]*Manifest, error)
 	return attestationManifests, nil
 }
 
-// GetAttestationsFromImage extracts all attestation layers from an image.
-func GetAttestationsFromImage(image v1.Image) ([]*Layer, error) {
+// LayersFromImage extracts all attestation layers from an image.
+func layersFromImage(image v1.Image) ([]*Layer, error) {
 	layers, err := image.Layers()
 	if err != nil {
 		return nil, fmt.Errorf("failed to extract layers from image: %w", err)
@@ -94,7 +108,7 @@ func GetAttestationsFromImage(image v1.Image) ([]*Layer, error) {
 	return attestationLayers, nil
 }
 
-func (manifest *Manifest) AddAttestation(ctx context.Context, signer dsse.SignerVerifier, statement *intoto.Statement, opts *SigningOptions) error {
+func (manifest *Manifest) Add(ctx context.Context, signer dsse.SignerVerifier, statement *intoto.Statement, opts *SigningOptions) error {
 	layer, err := createSignedImageLayer(ctx, statement, signer, opts)
 	if err != nil {
 		return fmt.Errorf("failed to create signed layer: %w", err)
@@ -105,7 +119,7 @@ func (manifest *Manifest) AddAttestation(ctx context.Context, signer dsse.Signer
 
 func createSignedImageLayer(ctx context.Context, statement *intoto.Statement, signer dsse.SignerVerifier, opts *SigningOptions) (*Layer, error) {
 	// sign the statement
-	env, err := SignInTotoStatement(ctx, statement, signer, opts)
+	env, err := signInTotoStatement(ctx, statement, signer, opts)
 	if err != nil {
 		return nil, fmt.Errorf("failed to sign statement: %w", err)
 	}
@@ -128,7 +142,7 @@ func createSignedImageLayer(ctx context.Context, statement *intoto.Statement, si
 	}, nil
 }
 
-func SignInTotoStatement(ctx context.Context, statement *intoto.Statement, signer dsse.SignerVerifier, opts *SigningOptions) (*Envelope, error) {
+func signInTotoStatement(ctx context.Context, statement *intoto.Statement, signer dsse.SignerVerifier, opts *SigningOptions) (*Envelope, error) {
 	payload, err := json.Marshal(statement)
 	if err != nil {
 		return nil, fmt.Errorf("failed to marshal statement: %w", err)
@@ -140,12 +154,12 @@ func SignInTotoStatement(ctx context.Context, statement *intoto.Statement, signe
 	return env, nil
 }
 
-func UpdateIndexImage(
+func updateImageIndex(
 	idx v1.ImageIndex,
 	manifest *Manifest,
 	options ...func(*ManifestImageOptions) error,
 ) (v1.ImageIndex, error) {
-	image, err := manifest.BuildAttestationImage(options...)
+	image, err := manifest.BuildImage(options...)
 	if err != nil {
 		return nil, fmt.Errorf("failed to build image: %w", err)
 	}
@@ -170,7 +184,7 @@ func UpdateIndexImage(
 func UpdateIndexImages(idx v1.ImageIndex, manifest []*Manifest, options ...func(*ManifestImageOptions) error) (v1.ImageIndex, error) {
 	var err error
 	for _, m := range manifest {
-		idx, err = UpdateIndexImage(idx, m, options...)
+		idx, err = updateImageIndex(idx, m, options...)
 		if err != nil {
 			return nil, fmt.Errorf("failed to add image to index: %w", err)
 		}
@@ -204,7 +218,7 @@ func WithReplacedLayers(replaceLayers bool) func(*ManifestImageOptions) error {
 }
 
 // build an image with signed attestations, optionally replacing existing layers with signed layers.
-func (manifest *Manifest) BuildAttestationImage(options ...func(*ManifestImageOptions) error) (v1.Image, error) {
+func (manifest *Manifest) BuildImage(options ...func(*ManifestImageOptions) error) (v1.Image, error) {
 	opts, err := newOptions(options...)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create options: %w", err)
@@ -229,7 +243,7 @@ func (manifest *Manifest) BuildAttestationImage(options ...func(*ManifestImageOp
 	}
 	// so that we attach all attestations to a single attestations image - as per current buildkit
 	opts.laxReferrers = true
-	newImg, err := buildImage(resultLayers, manifest.OriginalDescriptor, manifest.SubjectDescriptor, opts)
+	newImg, err := buildImageFromLayers(resultLayers, manifest.OriginalDescriptor, manifest.SubjectDescriptor, opts)
 	if err != nil {
 		return nil, fmt.Errorf("failed to build image: %w", err)
 	}
@@ -241,7 +255,7 @@ func (manifest *Manifest) BuildReferringArtifacts() ([]v1.Image, error) {
 	var images []v1.Image
 	for _, layer := range manifest.SignedLayers {
 		opts := &ManifestImageOptions{}
-		newImg, err := buildImage([]*Layer{layer}, manifest.OriginalDescriptor, manifest.SubjectDescriptor, opts)
+		newImg, err := buildImageFromLayers([]*Layer{layer}, manifest.OriginalDescriptor, manifest.SubjectDescriptor, opts)
 		if err != nil {
 			return nil, fmt.Errorf("failed to build image: %w", err)
 		}
@@ -250,8 +264,8 @@ func (manifest *Manifest) BuildReferringArtifacts() ([]v1.Image, error) {
 	return images, nil
 }
 
-// build an image containing only layers.
-func buildImage(layers []*Layer, manifest *v1.Descriptor, subject *v1.Descriptor, opts *ManifestImageOptions) (v1.Image, error) {
+// build an image containing only layers provided.
+func buildImageFromLayers(layers []*Layer, manifest *v1.Descriptor, subject *v1.Descriptor, opts *ManifestImageOptions) (v1.Image, error) {
 	newImg := empty.Image
 	var err error
 	if len(layers) == 0 {
@@ -296,46 +310,135 @@ func buildImage(layers []*Layer, manifest *v1.Descriptor, subject *v1.Descriptor
 	}
 	if !opts.laxReferrers {
 		// as per https://github.com/opencontainers/image-spec/blob/main/manifest.md#guidance-for-an-empty-descriptor
-		newImg = &EmptyConfigImage{newImg}
+		newImg = &oci.EmptyConfigImage{Image: newImg}
 	}
 	return newImg, nil
 }
 
-type EmptyConfigImage struct {
-	v1.Image
-}
-
-func (i *EmptyConfigImage) RawConfigFile() ([]byte, error) {
-	return []byte("{}"), nil
-}
-
-func (i *EmptyConfigImage) Manifest() (*v1.Manifest, error) {
-	mf, err := i.Image.Manifest()
+func ExtractEnvelopes(manifest *Manifest, predicateType string) ([]*Envelope, error) {
+	var envs []*Envelope
+	dsseMediaType, err := DSSEMediaType(predicateType)
 	if err != nil {
-		return nil, fmt.Errorf("failed to get manifest: %w", err)
+		return nil, fmt.Errorf("failed to get DSSE media type for predicate '%s': %w", predicateType, err)
 	}
-	mf.Config = v1.Descriptor{
-		MediaType: "application/vnd.oci.empty.v1+json",
-		Size:      2,
-		Digest:    v1.Hash{Algorithm: "sha256", Hex: "44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a"},
-		Data:      []byte("{}"),
+	for _, attestationLayer := range manifest.OriginalLayers {
+		mt, err := attestationLayer.Layer.MediaType()
+		if err != nil {
+			return nil, fmt.Errorf("failed to get layer media type: %w", err)
+		}
+		if string(mt) == dsseMediaType {
+			reader, err := attestationLayer.Layer.Uncompressed()
+			if err != nil {
+				return nil, fmt.Errorf("failed to get layer contents: %w", err)
+			}
+			defer reader.Close()
+			env := new(Envelope)
+			err = json.NewDecoder(reader).Decode(&env)
+			if err != nil {
+				return nil, fmt.Errorf("failed to decode envelope: %w", err)
+			}
+			envs = append(envs, env)
+		}
 	}
-	return mf, nil
+
+	return envs, nil
 }
 
-func (i *EmptyConfigImage) RawManifest() ([]byte, error) {
-	mf, err := i.Manifest()
+func ExtractStatementsFromIndex(idx v1.ImageIndex, mediaType string) ([]*AnnotatedStatement, error) {
+	mfs2, err := idx.IndexManifest()
 	if err != nil {
-		return nil, fmt.Errorf("failed to get manifest: %w", err)
+		return nil, fmt.Errorf("failed to extract IndexManifest from ImageIndex: %w", err)
 	}
-	return json.Marshal(mf)
+
+	var statements []*AnnotatedStatement
+
+	for i := range mfs2.Manifests {
+		mf := &mfs2.Manifests[i]
+		if mf.Annotations[DockerReferenceType] != "attestation-manifest" {
+			continue
+		}
+
+		attestationImage, err := idx.Image(mf.Digest)
+		if err != nil {
+			return nil, fmt.Errorf("failed to extract attestation image with digest %s: %w", mf.Digest.String(), err)
+		}
+		layers, err := attestationImage.Layers()
+		if err != nil {
+			return nil, fmt.Errorf("failed to extract layers from attestation image: %w", err)
+		}
+
+		for _, layer := range layers {
+			// parse layer blob as json
+			mt, err := layer.MediaType()
+			if err != nil {
+				return nil, fmt.Errorf("failed to get layer media type: %w", err)
+			}
+
+			if string(mt) != mediaType {
+				continue
+			}
+			r, err := layer.Uncompressed()
+			if err != nil {
+				return nil, fmt.Errorf("failed to get layer contents: %w", err)
+			}
+			defer r.Close()
+			inTotoStatement := new(intoto.Statement)
+			var desc *v1.Descriptor
+			if strings.HasSuffix(string(mt), "+dsse") {
+				env := new(Envelope)
+				err = json.NewDecoder(r).Decode(env)
+				if err != nil {
+					return nil, fmt.Errorf("failed to decode env: %w", err)
+				}
+				payload, err := base64.StdEncoding.Strict().DecodeString(env.Payload)
+				if err != nil {
+					return nil, fmt.Errorf("failed to decode payload: %w", err)
+				}
+				err = json.Unmarshal([]byte(payload), inTotoStatement)
+				if err != nil {
+					return nil, fmt.Errorf("failed to decode %s statement: %w", mediaType, err)
+				}
+			} else {
+				desc := new(v1.Descriptor)
+				err = json.NewDecoder(r).Decode(desc)
+				if err != nil {
+					return nil, fmt.Errorf("failed to decode statement: %w", err)
+				}
+			}
+
+			layerDesc, err := partial.Descriptor(layer)
+			if err != nil {
+				return nil, fmt.Errorf("failed to get descriptor for layer: %w", err)
+			}
+			annotations := make(map[string]string)
+			for k, v := range layerDesc.Annotations {
+				annotations[k] = v
+			}
+			statements = append(statements, &AnnotatedStatement{
+				OCIDescriptor:   desc,
+				InTotoStatement: inTotoStatement,
+				Annotations:     annotations,
+			})
+		}
+	}
+	return statements, nil
 }
 
-func (i *EmptyConfigImage) Digest() (v1.Hash, error) {
-	mb, err := i.RawManifest()
+func ExtractAnnotatedStatements(path string, mediaType string) ([]*AnnotatedStatement, error) {
+	idx, err := layout.ImageIndexFromPath(path)
 	if err != nil {
-		return v1.Hash{}, err
+		return nil, fmt.Errorf("failed to load image index: %w", err)
 	}
-	digest, _, err := v1.SHA256(bytes.NewReader(mb))
-	return digest, err
+
+	idxm, err := idx.IndexManifest()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get digest: %w", err)
+	}
+	idxDigest := idxm.Manifests[0].Digest
+
+	mfs, err := idx.ImageIndex(idxDigest)
+	if err != nil {
+		return nil, fmt.Errorf("failed to extract ImageIndex for digest %s: %w", idxDigest.String(), err)
+	}
+	return ExtractStatementsFromIndex(mfs, mediaType)
 }

pkg/attestation/attestation_test.go

@@ -1,21 +1,18 @@
-package test
+package attestation_test
 
 import (
-	"path/filepath"
 	"testing"
 
+	"github.com/docker/attest/internal/test"
+	"github.com/docker/attest/pkg/attestation"
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
 	"github.com/stretchr/testify/assert"
 )
 
-var UnsignedTestImage = filepath.Join("..", "..", "test", "testdata", "unsigned-test-image")
-
-const (
-	ExpectedStatements = 4
-)
+const ExpectedStatements = 4
 
 func TestExtractAnnotatedStatements(t *testing.T) {
-	statements, err := ExtractAnnotatedStatements(UnsignedTestImage, intoto.PayloadType)
+	statements, err := attestation.ExtractAnnotatedStatements(test.UnsignedTestImage, intoto.PayloadType)
 	assert.NoError(t, err)
 	assert.Equalf(t, len(statements), ExpectedStatements, "expected %d statement, got %d", ExpectedStatements, len(statements))
 }

pkg/attestation/example_attestation_manifest_test.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"time"
 
-	"github.com/docker/attest/pkg/attest"
 	"github.com/docker/attest/pkg/attestation"
 	"github.com/docker/attest/pkg/oci"
 	"github.com/docker/attest/pkg/signerverifier"
@@ -62,13 +61,13 @@ func ExampleManifest() {
 	}
 
 	// create a new manifest to hold the attestation
-	manifest, err := attest.NewAttestationManifest(desc)
+	manifest, err := attestation.NewManifest(desc)
 	if err != nil {
 		panic(err)
 	}
 
 	// sign and add the attestation to the manifest
-	err = manifest.AddAttestation(context.Background(), signer, statement, opts)
+	err = manifest.Add(context.Background(), signer, statement, opts)
 	if err != nil {
 		panic(err)
 	}
@@ -79,7 +78,11 @@ func ExampleManifest() {
 	}
 
 	// save the manifest to the registry as a referrers artifact
-	err = oci.SaveReferrers(manifest, output)
+	artifacts, err := manifest.BuildReferringArtifacts()
+	if err != nil {
+		panic(err)
+	}
+	err = oci.SaveImagesNoTag(artifacts, output)
 	if err != nil {
 		panic(err)
 	}

pkg/attestation/layout.go

@@ -1,36 +1,35 @@
-package oci
+package attestation
 
 import (
 	"context"
 	"encoding/json"
 	"fmt"
 
-	"github.com/docker/attest/pkg/attestation"
-	att "github.com/docker/attest/pkg/attestation"
+	"github.com/docker/attest/pkg/oci"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/layout"
 )
 
-// implementation of AttestationResolver that closes over attestations from an oci layout.
+// implementation of Resolver that closes over attestations from an oci layout.
 type LayoutResolver struct {
-	*attestation.Manifest
-	*ImageSpec
+	*Manifest
+	*oci.ImageSpec
 }
 
-func NewOCILayoutAttestationResolver(src *ImageSpec) (*LayoutResolver, error) {
+func NewOCILayoutResolver(src *oci.ImageSpec) (*LayoutResolver, error) {
 	r := &LayoutResolver{
 		ImageSpec: src,
 	}
-	_, err := r.fetchAttestationManifest()
+	_, err := r.fetchManifest()
 	if err != nil {
 		return nil, err
 	}
 	return r, nil
 }
 
-func (r *LayoutResolver) fetchAttestationManifest() (*attestation.Manifest, error) {
+func (r *LayoutResolver) fetchManifest() (*Manifest, error) {
 	if r.Manifest == nil {
-		m, err := attestationManifestFromOCILayout(r.Identifier, r.ImageSpec.Platform)
+		m, err := manifestFromOCILayout(r.Identifier, r.ImageSpec.Platform)
 		if err != nil {
 			return nil, err
 		}
@@ -40,9 +39,9 @@ func (r *LayoutResolver) fetchAttestationManifest() (*attestation.Manifest, erro
 	return r.Manifest, nil
 }
 
-func (r *LayoutResolver) Attestations(_ context.Context, predicateType string) ([]*att.Envelope, error) {
-	var envs []*att.Envelope
-	dsseMediaType, err := attestation.DSSEMediaType(predicateType)
+func (r *LayoutResolver) Attestations(_ context.Context, predicateType string) ([]*Envelope, error) {
+	var envs []*Envelope
+	dsseMediaType, err := DSSEMediaType(predicateType)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get DSSE media type for predicate '%s': %w", predicateType, err)
 	}
@@ -55,7 +54,7 @@ func (r *LayoutResolver) Attestations(_ context.Context, predicateType string) (
 		if mts != dsseMediaType {
 			continue
 		}
-		env := new(att.Envelope)
+		env := new(Envelope)
 		// parse layer blob as json
 		r, err := attestationLayer.Layer.Uncompressed()
 		if err != nil {
@@ -83,7 +82,7 @@ func (r *LayoutResolver) ImagePlatform(_ context.Context) (*v1.Platform, error)
 	return r.ImageSpec.Platform, nil
 }
 
-func attestationManifestFromOCILayout(path string, platform *v1.Platform) (*attestation.Manifest, error) {
+func manifestFromOCILayout(path string, platform *v1.Platform) (*Manifest, error) {
 	idx, err := layout.ImageIndexFromPath(path)
 	if err != nil {
 		return nil, err
@@ -120,11 +119,11 @@ func attestationManifestFromOCILayout(path string, platform *v1.Platform) (*atte
 	}
 	for i := range mfs2.Manifests {
 		mf := &mfs2.Manifests[i]
-		if mf.Annotations[att.DockerReferenceType] != attestation.AttestationManifestType {
+		if mf.Annotations[DockerReferenceType] != AttestationManifestType {
 			continue
 		}
 
-		if mf.Annotations[att.DockerReferenceDigest] != subjectDescriptor.Digest.String() {
+		if mf.Annotations[DockerReferenceDigest] != subjectDescriptor.Digest.String() {
 			continue
 		}
 
@@ -132,11 +131,11 @@ func attestationManifestFromOCILayout(path string, platform *v1.Platform) (*atte
 		if err != nil {
 			return nil, fmt.Errorf("failed to extract attestation image with digest %s: %w", mf.Digest.String(), err)
 		}
-		layers, err := attestation.GetAttestationsFromImage(attestationImage)
+		layers, err := layersFromImage(attestationImage)
 		if err != nil {
 			return nil, fmt.Errorf("failed to get attestations from image: %w", err)
 		}
-		attest := &attestation.Manifest{
+		attest := &Manifest{
 			OriginalLayers:     layers,
 			OriginalDescriptor: mf,
 			SubjectName:        idxDescriptor.Annotations["org.opencontainers.image.ref.name"],

pkg/attestation/layout_test.go

@@ -1,4 +1,4 @@
-package oci_test
+package attestation_test
 
 import (
 	"strings"
@@ -24,7 +24,7 @@ func TestAttestationFromOCILayout(t *testing.T) {
 	}
 
 	opts := &attestation.SigningOptions{}
-	attIdx, err := oci.IndexFromPath(oci.UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	require.NoError(t, err)
 	signedManifests, err := attest.SignStatements(ctx, attIdx.Index, signer, opts)
 	require.NoError(t, err)

pkg/attestation/mock.go

@@ -1,17 +1,17 @@
-package oci
+package attestation
 
 import (
 	"context"
 
-	"github.com/docker/attest/pkg/attestation"
+	"github.com/docker/attest/pkg/oci"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 )
 
 type MockResolver struct {
-	Envs []*attestation.Envelope
+	Envs []*Envelope
 }
 
-func (r MockResolver) Attestations(_ context.Context, _ string) ([]*attestation.Envelope, error) {
+func (r MockResolver) Attestations(_ context.Context, _ string) ([]*Envelope, error) {
 	return r.Envs, nil
 }
 
@@ -32,7 +32,7 @@ func (r MockResolver) ImageDescriptor(_ context.Context) (*v1.Descriptor, error)
 }
 
 func (r MockResolver) ImagePlatform(_ context.Context) (*v1.Platform, error) {
-	return ParsePlatform("linux/amd64")
+	return oci.ParsePlatform("linux/amd64")
 }
 
 type MockRegistryResolver struct {

pkg/attestation/referrers.go

@@ -1,22 +1,21 @@
-package oci
+package attestation
 
 import (
 	"context"
 	"fmt"
 	"strings"
 
-	"github.com/docker/attest/pkg/attestation"
-	att "github.com/docker/attest/pkg/attestation"
+	"github.com/docker/attest/pkg/oci"
 	"github.com/google/go-containerregistry/pkg/name"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 )
 
 type ReferrersResolver struct {
 	referrersRepo string
-	ImageDetailsResolver
+	oci.ImageDetailsResolver
 }
 
-func NewReferrersAttestationResolver(src ImageDetailsResolver, options ...func(*ReferrersResolver) error) (*ReferrersResolver, error) {
+func NewReferrersResolver(src oci.ImageDetailsResolver, options ...func(*ReferrersResolver) error) (*ReferrersResolver, error) {
 	res := &ReferrersResolver{
 		ImageDetailsResolver: src,
 	}
@@ -36,8 +35,8 @@ func WithReferrersRepo(repo string) func(*ReferrersResolver) error {
 	}
 }
 
-func (r *ReferrersResolver) resolveAttestations(ctx context.Context, predicateType string) ([]*attestation.Manifest, error) {
-	dsseMediaType, err := attestation.DSSEMediaType(predicateType)
+func (r *ReferrersResolver) resolveAttestations(ctx context.Context, predicateType string) ([]*Manifest, error) {
+	dsseMediaType, err := DSSEMediaType(predicateType)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get DSSE media type for predicate '%s': %w", predicateType, err)
 	}
@@ -54,19 +53,16 @@ func (r *ReferrersResolver) resolveAttestations(ctx context.Context, predicateTy
 		return nil, fmt.Errorf("failed to get descriptor: %w", err)
 	}
 	subjectDigest := desc.Digest.String()
-	if err != nil {
-		return nil, fmt.Errorf("failed to get digest: %w", err)
-	}
 	var referrersSubjectRef name.Digest
 	if r.referrersRepo != "" {
-		referrersSubjectRef, err = name.NewDigest(fmt.Sprintf("%s@%s", strings.TrimPrefix(r.referrersRepo, RegistryPrefix), subjectDigest))
+		referrersSubjectRef, err = name.NewDigest(fmt.Sprintf("%s@%s", strings.TrimPrefix(r.referrersRepo, oci.RegistryPrefix), subjectDigest))
 		if err != nil {
 			return nil, fmt.Errorf("failed to create referrers reference: %w", err)
 		}
 	} else {
 		referrersSubjectRef = subjectRef.Context().Digest(subjectDigest)
 	}
-	options := WithOptions(ctx, nil)
+	options := oci.WithOptions(ctx, nil)
 	options = append(options, remote.WithFilter("artifactType", dsseMediaType))
 	referrersIndex, err := remote.Referrers(referrersSubjectRef, options...)
 	if err != nil {
@@ -76,16 +72,16 @@ func (r *ReferrersResolver) resolveAttestations(ctx context.Context, predicateTy
 	if err != nil {
 		return nil, fmt.Errorf("failed to get index manifest: %w", err)
 	}
-	aManifests := make([]*attestation.Manifest, 0)
+	aManifests := make([]*Manifest, 0)
 	for i := range referrersIndexManifest.Manifests {
 		m := referrersIndexManifest.Manifests[i]
 		remoteRef := referrersSubjectRef.Context().Digest(m.Digest.String())
-		options = WithOptions(ctx, nil)
+		options = oci.WithOptions(ctx, nil)
 		attestationImage, err := remote.Image(remoteRef, options...)
 		if err != nil {
 			return nil, fmt.Errorf("failed to get referred image: %w", err)
 		}
-		layers, err := attestation.GetAttestationsFromImage(attestationImage)
+		layers, err := layersFromImage(attestationImage)
 		if err != nil {
 			return nil, fmt.Errorf("failed to get attestations from image: %w", err)
 		}
@@ -99,7 +95,7 @@ func (r *ReferrersResolver) resolveAttestations(ctx context.Context, predicateTy
 		if string(mt) != dsseMediaType {
 			return nil, fmt.Errorf("expected layer media type %s, got %s", dsseMediaType, mt)
 		}
-		attest := &attestation.Manifest{
+		attest := &Manifest{
 			SubjectName:        imageName,
 			OriginalLayers:     layers,
 			OriginalDescriptor: &m,
@@ -110,12 +106,12 @@ func (r *ReferrersResolver) resolveAttestations(ctx context.Context, predicateTy
 	return aManifests, nil
 }
 
-func (r *ReferrersResolver) Attestations(ctx context.Context, predicateType string) ([]*att.Envelope, error) {
+func (r *ReferrersResolver) Attestations(ctx context.Context, predicateType string) ([]*Envelope, error) {
 	manifests, err := r.resolveAttestations(ctx, predicateType)
 	if err != nil {
 		return nil, fmt.Errorf("failed to resolve attestations: %w", err)
 	}
-	var envs []*att.Envelope
+	var envs []*Envelope
 	for _, attest := range manifests {
 		es, err := ExtractEnvelopes(attest, predicateType)
 		if err != nil {

pkg/attestation/referrers_test.go

@@ -8,7 +8,6 @@ import (
 	"testing"
 
 	"github.com/docker/attest/internal/test"
-	"github.com/docker/attest/internal/util"
 	"github.com/docker/attest/pkg/attest"
 	"github.com/docker/attest/pkg/attestation"
 	"github.com/docker/attest/pkg/config"
@@ -16,14 +15,12 @@ import (
 	"github.com/docker/attest/pkg/policy"
 	"github.com/google/go-containerregistry/pkg/name"
 	"github.com/google/go-containerregistry/pkg/registry"
-	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
 var (
-	UnsignedTestImage   = filepath.Join("..", "..", "test", "testdata", "unsigned-test-image")
 	NoProvenanceImage   = filepath.Join("..", "..", "test", "testdata", "no-provenance-image")
 	PassPolicyDir       = filepath.Join("..", "..", "test", "testdata", "local-policy-pass")
 	LocalPolicy         = filepath.Join("..", "..", "test", "testdata", "local-policy")
@@ -94,7 +91,7 @@ func TestAttestationReferenceTypes(t *testing.T) {
 			opts := &attestation.SigningOptions{
 				SkipTL: true,
 			}
-			attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+			attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 			require.NoError(t, err)
 
 			indexName := fmt.Sprintf("%s/repo:root", u.Host)
@@ -120,7 +117,9 @@ func TestAttestationReferenceTypes(t *testing.T) {
 			output, err := oci.ParseImageSpec(outputRepo)
 			require.NoError(t, err)
 			for _, attIdx := range signedManifests {
-				err = oci.SaveReferrers(attIdx, []*oci.ImageSpec{output})
+				images, err := attIdx.BuildReferringArtifacts()
+				require.NoError(t, err)
+				err = oci.SaveImagesNoTag(images, []*oci.ImageSpec{output})
 				require.NoError(t, err)
 			}
 
@@ -213,7 +212,7 @@ func TestReferencesInDifferentRepo(t *testing.T) {
 		opts := &attestation.SigningOptions{
 			SkipTL: true,
 		}
-		attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+		attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 		require.NoError(t, err)
 
 		indexName := fmt.Sprintf("%s/%s:latest", serverURL.Host, repoName)
@@ -226,7 +225,7 @@ func TestReferencesInDifferentRepo(t *testing.T) {
 		// push signed attestation image to the ref server
 		for _, signedManifest := range signedManifests {
 			// push references using subject-digest.att convention
-			image, err := signedManifest.BuildAttestationImage()
+			image, err := signedManifest.BuildImage()
 			require.NoError(t, err)
 			err = oci.PushImageToRegistry(image, fmt.Sprintf("%s/%s:tag-does-not-matter", refServerURL.Host, repoName))
 			require.NoError(t, err)
@@ -239,7 +238,7 @@ func TestReferencesInDifferentRepo(t *testing.T) {
 			opts := &attestation.SigningOptions{
 				SkipTL: true,
 			}
-			attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+			attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 			require.NoError(t, err)
 
 			indexName := fmt.Sprintf("%s/%s:latest", serverURL.Host, repoName)
@@ -294,7 +293,7 @@ func TestCorrectArtifactTypeInTagFallback(t *testing.T) {
 	opts := &attestation.SigningOptions{
 		SkipTL: true,
 	}
-	attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	require.NoError(t, err)
 
 	indexName := fmt.Sprintf("%s/%s:latest", serverURL.Host, repoName)
@@ -327,14 +326,3 @@ func TestCorrectArtifactTypeInTagFallback(t *testing.T) {
 		}
 	}
 }
-
-func TestEmptyConfigImageDigest(t *testing.T) {
-	empty := empty.Image
-	img := attestation.EmptyConfigImage{empty}
-	mf, err := img.RawManifest()
-	require.NoError(t, err)
-	hash := util.SHA256Hex(mf)
-	digest, err := img.Digest()
-	require.NoError(t, err)
-	assert.Equal(t, digest.Hex, hash)
-}

pkg/attestation/registry.go

@@ -0,0 +1,101 @@
+package attestation
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/docker/attest/pkg/oci"
+	"github.com/google/go-containerregistry/pkg/name"
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/remote"
+)
+
+type RegistryResolver struct {
+	*oci.RegistryImageDetailsResolver
+	*Manifest
+}
+
+func NewRegistryResolver(src *oci.RegistryImageDetailsResolver) (*RegistryResolver, error) {
+	return &RegistryResolver{
+		RegistryImageDetailsResolver: src,
+	}, nil
+}
+
+func (r *RegistryResolver) Attestations(ctx context.Context, predicateType string) ([]*Envelope, error) {
+	if r.Manifest == nil {
+		attest, err := FetchManifest(ctx, r.Identifier, r.ImageSpec.Platform)
+		if err != nil {
+			return nil, err
+		}
+		r.Manifest = attest
+	}
+	return ExtractEnvelopes(r.Manifest, predicateType)
+}
+
+func attestationDigestForImage(ix *v1.IndexManifest, imageDigest string, attestType string) (string, error) {
+	for i := range ix.Manifests {
+		m := &ix.Manifests[i]
+		if v, ok := m.Annotations[DockerReferenceType]; ok && v == attestType {
+			if d, ok := m.Annotations[DockerReferenceDigest]; ok && d == imageDigest {
+				return m.Digest.String(), nil
+			}
+		}
+	}
+	return "", fmt.Errorf("no attestation found for image %s", imageDigest)
+}
+
+func FetchManifest(ctx context.Context, image string, platform *v1.Platform) (*Manifest, error) {
+	// we want to get to the image index, so ignoring platform for now
+	options := oci.WithOptions(ctx, nil)
+	ref, err := name.ParseReference(image)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse reference: %w", err)
+	}
+	index, err := remote.Index(ref, options...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get index: %w", err)
+	}
+	indexManifest, err := index.IndexManifest()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get index manifest: %w", err)
+	}
+	subjectDescriptor, err := oci.ImageDescriptor(indexManifest, platform)
+	if err != nil {
+		return nil, fmt.Errorf("failed to obtain image for platform: %w", err)
+	}
+
+	digest := subjectDescriptor.Digest.String()
+	ref, err = name.ParseReference(fmt.Sprintf("%s@%s", ref.Context().Name(), digest))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse attestation reference: %w", err)
+	}
+
+	attestationDigest, err := attestationDigestForImage(indexManifest, digest, "attestation-manifest")
+	if err != nil {
+		return nil, fmt.Errorf("failed to obtain attestation for image: %w", err)
+	}
+	ref, err = name.ParseReference(fmt.Sprintf("%s@%s", ref.Context().Name(), attestationDigest))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse attestation reference: %w", err)
+	}
+	remoteDescriptor, err := remote.Get(ref, options...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get attestation: %w", err)
+	}
+	attestationImage, err := remoteDescriptor.Image()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get attestation image: %w", err)
+	}
+
+	layers, err := layersFromImage(attestationImage)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get attestations from image: %w", err)
+	}
+	attest := &Manifest{
+		OriginalLayers:     layers,
+		OriginalDescriptor: &remoteDescriptor.Descriptor,
+		SubjectName:        image,
+		SubjectDescriptor:  subjectDescriptor,
+	}
+	return attest, nil
+}

pkg/attestation/registry_test.go

@@ -1,4 +1,4 @@
-package oci_test
+package attestation_test
 
 import (
 	"fmt"
@@ -25,7 +25,7 @@ func TestRegistry(t *testing.T) {
 	require.NoError(t, err)
 
 	opts := &attestation.SigningOptions{}
-	attIdx, err := oci.IndexFromPath(oci.UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	require.NoError(t, err)
 	signedManifests, err := attest.SignStatements(ctx, attIdx.Index, signer, opts)
 	require.NoError(t, err)

pkg/attestation/resolver.go

@@ -0,0 +1,12 @@
+package attestation
+
+import (
+	"context"
+
+	"github.com/docker/attest/pkg/oci"
+)
+
+type Resolver interface {
+	oci.ImageDetailsResolver
+	Attestations(ctx context.Context, mediaType string) ([]*Envelope, error)
+}

pkg/attestation/sign_test.go

@@ -6,12 +6,19 @@ import (
 	"crypto/rand"
 	"encoding/json"
 	"fmt"
+	"net/http/httptest"
+	"net/url"
 	"testing"
 	"time"
 
 	"github.com/docker/attest/internal/test"
 	"github.com/docker/attest/pkg/attestation"
+	"github.com/docker/attest/pkg/oci"
 	"github.com/docker/attest/pkg/signerverifier"
+	"github.com/google/go-containerregistry/pkg/registry"
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/static"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -149,3 +156,146 @@ func TestSignVerifyAttestation(t *testing.T) {
 		})
 	}
 }
+
+func TestAddSignedLayerAnnotations(t *testing.T) {
+	ctx, signer := test.Setup(t)
+	testCases := []struct {
+		name    string
+		replace bool
+	}{
+		{"replaced", true},
+		{"not replaced", false},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			data := []byte("signed")
+			testLayer := static.NewLayer(data, types.MediaType(intoto.PayloadType))
+			mediaType := types.OCIManifestSchema1
+			opts := &attestation.SigningOptions{}
+			originalLayer := &attestation.Layer{
+				Layer: testLayer,
+				Statement: &intoto.Statement{
+					StatementHeader: intoto.StatementHeader{
+						PredicateType: attestation.VSAPredicateType,
+					},
+				},
+				Annotations: map[string]string{"test": "test"},
+			}
+
+			manifest := &attestation.Manifest{
+				OriginalDescriptor: &v1.Descriptor{
+					MediaType: mediaType,
+				},
+				OriginalLayers: []*attestation.Layer{
+					originalLayer,
+				},
+				SubjectDescriptor: &v1.Descriptor{},
+			}
+			err := manifest.Add(ctx, signer, originalLayer.Statement, opts)
+			require.NoError(t, err)
+
+			newImg, err := manifest.BuildImage(attestation.WithReplacedLayers(tc.replace))
+			require.NoError(t, err)
+			mf, _ := newImg.RawManifest()
+			type Annotations struct {
+				Annotations map[string]string `json:"annotations"`
+			}
+			type Layers struct {
+				Layers []Annotations `json:"layers"`
+			}
+			l := &Layers{}
+			err = json.Unmarshal(mf, l)
+			require.NoError(t, err)
+			_, ok := l.Layers[0].Annotations["test"]
+			assert.Truef(t, ok, "missing annotations")
+		})
+	}
+}
+
+func TestSimpleStatementSigning(t *testing.T) {
+	ctx, signer := test.Setup(t)
+	empty := types.MediaType("application/vnd.oci.empty.v1+json")
+	testCases := []struct {
+		name    string
+		replace bool
+	}{
+		{"replaced", true},
+		{"not replaced", false},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			opts := &attestation.SigningOptions{}
+			statement := &intoto.Statement{
+				StatementHeader: intoto.StatementHeader{
+					PredicateType: attestation.VSAPredicateType,
+				},
+			}
+			statement2 := &intoto.Statement{
+				StatementHeader: intoto.StatementHeader{
+					PredicateType: attestation.VSAPredicateType,
+				},
+			}
+			digest, err := v1.NewHash("sha256:da8b190665956ea07890a0273e2a9c96bfe291662f08e2860e868eef69c34620")
+			require.NoError(t, err)
+			subject := &v1.Descriptor{
+				MediaType: "application/vnd.oci.image.manifest.v1+json",
+				Digest:    digest,
+			}
+			manifest, err := attestation.NewManifest(subject)
+			require.NoError(t, err)
+			err = manifest.Add(ctx, signer, statement, opts)
+			require.NoError(t, err)
+
+			err = manifest.Add(ctx, signer, statement2, opts)
+			require.NoError(t, err)
+
+			// fake that the manfifest was loaded from a real image
+			manifest.OriginalLayers = manifest.SignedLayers
+			envelopes, err := attestation.ExtractEnvelopes(manifest, attestation.VSAPredicateType)
+			require.NoError(t, err)
+			assert.Len(t, envelopes, 2)
+
+			newImg, err := manifest.BuildImage(attestation.WithReplacedLayers(tc.replace))
+			require.NoError(t, err)
+			layers, err := newImg.Layers()
+			require.NoError(t, err)
+			if tc.replace {
+				assert.Len(t, layers, 2)
+			} else {
+				assert.Len(t, layers, 4)
+			}
+
+			newImgs, err := manifest.BuildReferringArtifacts()
+			require.NoError(t, err)
+			assert.Len(t, newImgs, 2)
+			for _, img := range newImgs {
+				mf, err := img.Manifest()
+				require.NoError(t, err)
+				assert.Contains(t, mf.ArtifactType, "application/vnd.in-toto")
+				assert.Contains(t, mf.ArtifactType, "+dsse")
+				assert.Equal(t, subject.MediaType, mf.MediaType)
+				assert.Equal(t, empty, mf.Config.MediaType)
+				assert.Equal(t, int64(2), mf.Config.Size)
+				assert.Equal(t, "{}", string(mf.Config.Data))
+				layers, err := img.Layers()
+				require.NoError(t, err)
+				assert.Len(t, layers, 1)
+			}
+			server := httptest.NewServer(registry.New(registry.WithReferrersSupport(true)))
+			defer server.Close()
+
+			u, err := url.Parse(server.URL)
+			require.NoError(t, err)
+
+			indexName := fmt.Sprintf("%s/repo:root", u.Host)
+			output, err := oci.ParseImageSpecs(indexName)
+			require.NoError(t, err)
+			artifacts, err := manifest.BuildReferringArtifacts()
+			require.NoError(t, err)
+			err = oci.SaveImagesNoTag(artifacts, output)
+			require.NoError(t, err)
+		})
+	}
+}

pkg/attestation/types.go

@@ -64,6 +64,12 @@ type Extension struct {
 	Ext  *DockerDSSEExtension `json:"ext"`
 }
 
+type AnnotatedStatement struct {
+	OCIDescriptor   *v1.Descriptor
+	InTotoStatement *intoto.Statement
+	Annotations     map[string]string
+}
+
 type DockerDSSEExtension struct {
 	TL *DockerTLExtension `json:"tl"`
 }
@@ -83,6 +89,12 @@ type SigningOptions struct {
 	SkipTL bool
 }
 
+type Options struct {
+	NoReferrers   bool
+	Attach        bool
+	ReferrersRepo string
+}
+
 func DSSEMediaType(predicateType string) (string, error) {
 	var predicateName string
 	switch predicateType {

pkg/attestation/vsa.go

@@ -16,7 +16,7 @@ type VSAPredicate struct {
 	TimeVerified       string                `json:"timeVerified"`
 	ResourceURI        string                `json:"resourceUri"`
 	Policy             VSAPolicy             `json:"policy"`
-	InputAttestations  []VSAInputAttestation `json:"inputAttestations"`
+	InputAttestations  []VSAInputAttestation `json:"inputAttestations,omitempty"`
 	VerificationResult string                `json:"verificationResult"`
 	VerifiedLevels     []string              `json:"verifiedLevels"`
 }
@@ -26,7 +26,9 @@ type VSAVerifier struct {
 }
 
 type VSAPolicy struct {
-	URI string `json:"uri"`
+	URI              string            `json:"uri,omitempty"`
+	Digest           map[string]string `json:"digest"`
+	DownloadLocation string            `json:"downloadLocation,omitempty"`
 }
 
 type VSAInputAttestation struct {

pkg/config/config.go

@@ -36,13 +36,13 @@ func LoadTUFMappings(tufClient tuf.Downloader, localTargetsDir string) (*PolicyM
 		return nil, fmt.Errorf("tuf client not set")
 	}
 	filename := MappingFilename
-	_, fileContents, err := tufClient.DownloadTarget(filename, filepath.Join(localTargetsDir, filename))
+	file, err := tufClient.DownloadTarget(filename, filepath.Join(localTargetsDir, filename))
 	if err != nil {
 		return nil, fmt.Errorf("failed to download policy mapping file %s: %w", filename, err)
 	}
 	mappings := &policyMappingsFile{}
 
-	err = yaml.Unmarshal(fileContents, mappings)
+	err = yaml.Unmarshal(file.Data, mappings)
 	if err != nil {
 		return nil, fmt.Errorf("failed to unmarshal policy mapping file %s: %w", filename, err)
 	}

pkg/mirror/README.md

@@ -0,0 +1,2 @@
+## mirror
+This package contains components to mirror TUF metadata and targets to OCI.

pkg/mirror/metadata.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strconv"
 
+	"github.com/docker/attest/pkg/oci"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
@@ -17,7 +18,7 @@ import (
 // -----------------
 
 // GetMetadataManifest returns an image with TUF root metadata as layers.
-func (m *TUFMirror) GetMetadataManifest(metadataURL string) (v1.Image, error) {
+func (m *TUFMirror) GetMetadataManifest(metadataURL string) (*oci.EmptyConfigImage, error) {
 	metadata, err := m.getMetadataMirror(metadataURL)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get metadata: %w", err)
@@ -26,7 +27,7 @@ func (m *TUFMirror) GetMetadataManifest(metadataURL string) (v1.Image, error) {
 	if err != nil {
 		return nil, fmt.Errorf("failed to build metadata manifest: %w", err)
 	}
-	return manifest, nil
+	return &oci.EmptyConfigImage{Image: manifest}, nil
 }
 
 // getMetadataMirror returns a TufMetadata struct with TUF metadata as map of file names to bytes.
@@ -183,7 +184,7 @@ func (m *TUFMirror) buildDelegatedMetadataManifests(delegated []DelegatedTargetM
 		if err != nil {
 			return nil, fmt.Errorf("failed to append delegated targets layer to image: %w", err)
 		}
-		manifests = append(manifests, &Image{Image: img, Tag: role.Name})
+		manifests = append(manifests, &Image{Image: &oci.EmptyConfigImage{Image: img}, Tag: role.Name})
 	}
 	return manifests, nil
 }

pkg/mirror/metadata_test.go

@@ -16,15 +16,20 @@ import (
 	"github.com/theupdateframework/go-tuf/v2/metadata"
 )
 
+const (
+	metadataPath = "/metadata"
+	targetsPath  = "/targets"
+)
+
 func TestGetTufMetadataMirror(t *testing.T) {
 	server := httptest.NewServer(http.FileServer(http.Dir(filepath.Join("..", "..", "test", "testdata", "tuf", "test-repo"))))
 	defer server.Close()
 
 	path := test.CreateTempDir(t, "", "tuf_temp")
-	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+"/metadata", server.URL+"/targets", tuf.NewMockVersionChecker())
+	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+metadataPath, server.URL+targetsPath, tuf.NewMockVersionChecker())
 	assert.NoError(t, err)
 
-	tufMetadata, err := m.getMetadataMirror(server.URL + "/metadata")
+	tufMetadata, err := m.getMetadataMirror(server.URL + metadataPath)
 	assert.NoError(t, err)
 
 	// check that all roles are not empty
@@ -39,10 +44,10 @@ func TestGetMetadataManifest(t *testing.T) {
 	defer server.Close()
 
 	path := test.CreateTempDir(t, "", "tuf_temp")
-	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+"/metadata", server.URL+"/targets", tuf.NewMockVersionChecker())
+	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+metadataPath, server.URL+targetsPath, tuf.NewMockVersionChecker())
 	assert.NoError(t, err)
 
-	img, err := m.GetMetadataManifest(server.URL + "/metadata")
+	img, err := m.GetMetadataManifest(server.URL + metadataPath)
 	assert.NoError(t, err)
 	assert.NotNil(t, img)
 
@@ -78,7 +83,7 @@ func TestGetDelegatedMetadataMirrors(t *testing.T) {
 	defer server.Close()
 
 	path := test.CreateTempDir(t, "", "tuf_temp")
-	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+"/metadata", server.URL+"/targets", tuf.NewMockVersionChecker())
+	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+metadataPath, server.URL+targetsPath, tuf.NewMockVersionChecker())
 	assert.NoError(t, err)
 
 	delegations, err := m.GetDelegatedMetadataMirrors()

pkg/mirror/targets.go

@@ -5,6 +5,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/docker/attest/pkg/oci"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
@@ -22,7 +23,7 @@ func (m *TUFMirror) GetTUFTargetMirrors() ([]*Image, error) {
 	targets := md.Targets[metadata.TARGETS].Signed.Targets
 	for _, t := range targets {
 		// download target file
-		_, data, err := m.TUFClient.DownloadTarget(t.Path, filepath.Join(m.tufPath, "download"))
+		file, err := m.TUFClient.DownloadTarget(t.Path, filepath.Join(m.tufPath, "download"))
 		if err != nil {
 			return nil, fmt.Errorf("failed to download target %s: %w", t.Path, err)
 		}
@@ -37,12 +38,12 @@ func (m *TUFMirror) GetTUFTargetMirrors() ([]*Image, error) {
 		}
 		name := hash.String() + "." + t.Path
 		ann := map[string]string{tufFileAnnotation: name}
-		layer := mutate.Addendum{Layer: static.NewLayer(data, tufTargetMediaType), Annotations: ann}
+		layer := mutate.Addendum{Layer: static.NewLayer(file.Data, tufTargetMediaType), Annotations: ann}
 		img, err = mutate.Append(img, layer)
 		if err != nil {
 			return nil, fmt.Errorf("failed to append role layer to image: %w", err)
 		}
-		targetMirrors = append(targetMirrors, &Image{Image: img, Tag: name})
+		targetMirrors = append(targetMirrors, &Image{Image: &oci.EmptyConfigImage{Image: img}, Tag: name})
 	}
 	return targetMirrors, nil
 }
@@ -68,7 +69,7 @@ func (m *TUFMirror) GetDelegatedTargetMirrors() ([]*Index, error) {
 		// for each target file, create an image with the target file as a layer
 		for _, target := range roleMeta.Signed.Targets {
 			// download target file
-			_, data, err := m.TUFClient.DownloadTarget(target.Path, filepath.Join(m.tufPath, "download"))
+			file, err := m.TUFClient.DownloadTarget(target.Path, filepath.Join(m.tufPath, "download"))
 			if err != nil {
 				return nil, fmt.Errorf("failed to download target %s: %w", target.Path, err)
 			}
@@ -88,14 +89,15 @@ func (m *TUFMirror) GetDelegatedTargetMirrors() ([]*Index, error) {
 			}
 			name := hash.String() + "." + filename
 			ann := map[string]string{tufFileAnnotation: name}
-			layer := mutate.Addendum{Layer: static.NewLayer(data, tufTargetMediaType), Annotations: ann}
+			layer := mutate.Addendum{Layer: static.NewLayer(file.Data, tufTargetMediaType), Annotations: ann}
 			img, err = mutate.Append(img, layer)
 			if err != nil {
 				return nil, fmt.Errorf("failed to append role layer to image: %w", err)
 			}
+			emptyConfigImage := &oci.EmptyConfigImage{Image: img}
 			// append image to index with annotation
 			index = mutate.AppendManifests(index, mutate.IndexAddendum{
-				Add: img,
+				Add: emptyConfigImage,
 				Descriptor: v1.Descriptor{
 					Annotations: map[string]string{
 						tufFileAnnotation: fmt.Sprintf("%s/%s", subdir, name),

pkg/mirror/targets_test.go

@@ -27,7 +27,7 @@ func TestGetTufTargetsMirror(t *testing.T) {
 	defer server.Close()
 
 	path := test.CreateTempDir(t, "", "tuf_temp")
-	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+"/metadata", server.URL+"/targets", tuf.NewMockVersionChecker())
+	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+metadataPath, server.URL+targetsPath, tuf.NewMockVersionChecker())
 	assert.NoError(t, err)
 
 	targets, err := m.GetTUFTargetMirrors()
@@ -61,7 +61,7 @@ func TestTargetDelegationMetadata(t *testing.T) {
 	defer server.Close()
 
 	path := test.CreateTempDir(t, "", "tuf_temp")
-	tm, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+"/metadata", server.URL+"/targets", tuf.NewMockVersionChecker())
+	tm, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+metadataPath, server.URL+targetsPath, tuf.NewMockVersionChecker())
 	assert.NoError(t, err)
 
 	targets, err := tm.TUFClient.LoadDelegatedTargets("test-role", "targets")
@@ -74,7 +74,7 @@ func TestGetDelegatedTargetMirrors(t *testing.T) {
 	defer server.Close()
 
 	path := test.CreateTempDir(t, "", "tuf_temp")
-	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+"/metadata", server.URL+"/targets", tuf.NewMockVersionChecker())
+	m, err := NewTUFMirror(embed.RootDev.Data, path, server.URL+metadataPath, server.URL+targetsPath, tuf.NewMockVersionChecker())
 	assert.NoError(t, err)
 
 	mirrors, err := m.GetDelegatedTargetMirrors()

pkg/mirror/types.go

@@ -1,6 +1,7 @@
 package mirror
 
 import (
+	"github.com/docker/attest/pkg/oci"
 	"github.com/docker/attest/pkg/tuf"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/theupdateframework/go-tuf/v2/metadata"
@@ -32,7 +33,7 @@ type DelegatedTargetMetadata struct {
 }
 
 type Image struct {
-	Image v1.Image
+	Image *oci.EmptyConfigImage
 	Tag   string
 }
 

pkg/oci/README.md

@@ -0,0 +1,2 @@
+## oci
+This package is for generic OCI components. For attestation specific components see the `attestation` package.

pkg/oci/authn_test.go

@@ -1,19 +1,17 @@
 //go:build e2e
 
-package mirror_test
+package oci_test
 
 import (
-	"path/filepath"
 	"testing"
 
+	"github.com/docker/attest/internal/test"
 	"github.com/docker/attest/pkg/oci"
 	"github.com/stretchr/testify/require"
 )
 
 func TestRegistryAuth(t *testing.T) {
-	UnsignedTestImage := filepath.Join("..", "..", "test", "testdata", "unsigned-test-image")
-
-	attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	require.NoError(t, err)
 	// test cases for ecr, gcr and dockerhub
 	testCases := []struct {

pkg/oci/oci.go

@@ -2,14 +2,11 @@ package oci
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"strings"
 
 	"github.com/containerd/platforms"
 	"github.com/distribution/reference"
-	"github.com/docker/attest/pkg/attestation"
-	att "github.com/docker/attest/pkg/attestation"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 	"github.com/in-toto/in-toto-golang/in_toto/slsa_provenance/common"
@@ -45,36 +42,7 @@ func WithOptions(ctx context.Context, platform *v1.Platform) []remote.Option {
 	return options
 }
 
-func ExtractEnvelopes(manifest *attestation.Manifest, predicateType string) ([]*att.Envelope, error) {
-	var envs []*att.Envelope
-	dsseMediaType, err := attestation.DSSEMediaType(predicateType)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get DSSE media type for predicate '%s': %w", predicateType, err)
-	}
-	for _, attestationLayer := range manifest.OriginalLayers {
-		mt, err := attestationLayer.Layer.MediaType()
-		if err != nil {
-			return nil, fmt.Errorf("failed to get layer media type: %w", err)
-		}
-		if string(mt) == dsseMediaType {
-			reader, err := attestationLayer.Layer.Uncompressed()
-			if err != nil {
-				return nil, fmt.Errorf("failed to get layer contents: %w", err)
-			}
-			defer reader.Close()
-			env := new(att.Envelope)
-			err = json.NewDecoder(reader).Decode(&env)
-			if err != nil {
-				return nil, fmt.Errorf("failed to decode envelope: %w", err)
-			}
-			envs = append(envs, env)
-		}
-	}
-
-	return envs, nil
-}
-
-func imageDescriptor(ix *v1.IndexManifest, platform *v1.Platform) (*v1.Descriptor, error) {
+func ImageDescriptor(ix *v1.IndexManifest, platform *v1.Platform) (*v1.Descriptor, error) {
 	for i := range ix.Manifests {
 		m := &ix.Manifests[i]
 		if (m.MediaType == ocispec.MediaTypeImageManifest || m.MediaType == "application/vnd.docker.distribution.manifest.v2+json") && m.Platform.Equals(*platform) {
@@ -84,18 +52,6 @@ func imageDescriptor(ix *v1.IndexManifest, platform *v1.Platform) (*v1.Descripto
 	return nil, fmt.Errorf("no image found for platform %v", platform)
 }
 
-func attestationDigestForDigest(ix *v1.IndexManifest, imageDigest string, attestType string) (string, error) {
-	for i := range ix.Manifests {
-		m := &ix.Manifests[i]
-		if v, ok := m.Annotations[att.DockerReferenceType]; ok && v == attestType {
-			if d, ok := m.Annotations[att.DockerReferenceDigest]; ok && d == imageDigest {
-				return m.Digest.String(), nil
-			}
-		}
-	}
-	return "", fmt.Errorf("no attestation found for image %s", imageDigest)
-}
-
 func RefToPURL(ref string, platform *v1.Platform) (string, bool, error) {
 	var isCanonical bool
 	named, err := reference.ParseNormalizedNamed(ref)
@@ -150,7 +106,7 @@ func SplitDigest(digest string) (common.DigestSet, error) {
 }
 
 func ReplaceTagInSpec(src *ImageSpec, digest v1.Hash) (*ImageSpec, error) {
-	newName, err := replaceTag(src.Identifier, digest)
+	newName, err := ReplaceTag(src.Identifier, digest)
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse repo name: %w", err)
 	}
@@ -162,7 +118,7 @@ func ReplaceTagInSpec(src *ImageSpec, digest v1.Hash) (*ImageSpec, error) {
 }
 
 // so that the index tag is replaced with a tag unique to the image digest and doesn't overwrite it.
-func replaceTag(image string, digest v1.Hash) (string, error) {
+func ReplaceTag(image string, digest v1.Hash) (string, error) {
 	if strings.HasPrefix(image, LocalPrefix) {
 		return image, nil
 	}

pkg/oci/oci_test.go

@@ -1,56 +1,55 @@
-package oci
+package oci_test
 
 import (
-	"path/filepath"
 	"testing"
 
+	"github.com/docker/attest/internal/test"
+	"github.com/docker/attest/pkg/oci"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/layout"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
-var UnsignedTestImage = filepath.Join("..", "..", "test", "testdata", "unsigned-test-image")
-
 func TestRefToPurl(t *testing.T) {
-	arm, err := ParsePlatform("arm64/linux")
+	arm, err := oci.ParsePlatform("arm64/linux")
 	require.NoError(t, err)
-	purl, canonical, err := RefToPURL("alpine", arm)
+	purl, canonical, err := oci.RefToPURL("alpine", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/alpine@latest?platform=arm64%2Flinux", purl)
 	assert.False(t, canonical)
 
-	purl, canonical, err = RefToPURL("alpine:123", arm)
+	purl, canonical, err = oci.RefToPURL("alpine:123", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/alpine@123?platform=arm64%2Flinux", purl)
 	assert.False(t, canonical)
 
-	purl, canonical, err = RefToPURL("google/alpine:123", arm)
+	purl, canonical, err = oci.RefToPURL("google/alpine:123", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/google/alpine@123?platform=arm64%2Flinux", purl)
 	assert.False(t, canonical)
 
-	purl, canonical, err = RefToPURL("library/alpine:123", arm)
+	purl, canonical, err = oci.RefToPURL("library/alpine:123", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/alpine@123?platform=arm64%2Flinux", purl)
 	assert.False(t, canonical)
 
-	purl, canonical, err = RefToPURL("docker.io/library/alpine:123", arm)
+	purl, canonical, err = oci.RefToPURL("docker.io/library/alpine:123", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/alpine@123?platform=arm64%2Flinux", purl)
 	assert.False(t, canonical)
 
-	purl, canonical, err = RefToPURL("localhost:5001/library/alpine:123", arm)
+	purl, canonical, err = oci.RefToPURL("localhost:5001/library/alpine:123", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/localhost%3A5001/library/alpine@123?platform=arm64%2Flinux", purl)
 	assert.False(t, canonical)
 
-	purl, canonical, err = RefToPURL("localhost:5001/alpine:123", arm)
+	purl, canonical, err = oci.RefToPURL("localhost:5001/alpine:123", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/localhost%3A5001/alpine@123?platform=arm64%2Flinux", purl)
 	assert.False(t, canonical)
 
-	purl, canonical, err = RefToPURL("localhost:5001/alpine@sha256:c5b1261d6d3e43071626931fc004f70149baeba2c8ec672bd4f27761f8e1ad6b", arm)
+	purl, canonical, err = oci.RefToPURL("localhost:5001/alpine@sha256:c5b1261d6d3e43071626931fc004f70149baeba2c8ec672bd4f27761f8e1ad6b", arm)
 	assert.NoError(t, err)
 	assert.Equal(t, "pkg:docker/localhost%3A5001/alpine?digest=sha256%3Ac5b1261d6d3e43071626931fc004f70149baeba2c8ec672bd4f27761f8e1ad6b&platform=arm64%2Flinux", purl)
 	assert.True(t, canonical)
@@ -58,7 +57,7 @@ func TestRefToPurl(t *testing.T) {
 
 // Test fix for https://github.com/docker/secure-artifacts-team-issues/issues/202
 func TestImageDigestForPlatform(t *testing.T) {
-	idx, err := layout.ImageIndexFromPath(UnsignedTestImage)
+	idx, err := layout.ImageIndexFromPath(test.UnsignedTestImage)
 	assert.NoError(t, err)
 
 	idxm, err := idx.IndexManifest()
@@ -72,16 +71,16 @@ func TestImageDigestForPlatform(t *testing.T) {
 	mfs2, err := mfs.IndexManifest()
 	assert.NoError(t, err)
 
-	p, err := ParsePlatform("linux/amd64")
+	p, err := oci.ParsePlatform("linux/amd64")
 	assert.NoError(t, err)
-	desc, err := imageDescriptor(mfs2, p)
+	desc, err := oci.ImageDescriptor(mfs2, p)
 	assert.NoError(t, err)
 	digest := desc.Digest.String()
 	assert.Equal(t, "sha256:da8b190665956ea07890a0273e2a9c96bfe291662f08e2860e868eef69c34620", digest)
 
-	p, err = ParsePlatform("linux/arm64")
+	p, err = oci.ParsePlatform("linux/arm64")
 	assert.NoError(t, err)
-	desc, err = imageDescriptor(mfs2, p)
+	desc, err = oci.ImageDescriptor(mfs2, p)
 	assert.NoError(t, err)
 	digest = desc.Digest.String()
 	assert.Equal(t, "sha256:7a76cec943853f9f7105b1976afa1bf7cd5bb6afc4e9d5852dd8da7cf81ae86e", digest)
@@ -95,14 +94,14 @@ func TestWithoutTag(t *testing.T) {
 		{name: "image:tag", expected: "index.docker.io/library/image"},
 		{name: "image", expected: "index.docker.io/library/image"},
 		{name: "image:sha256-digest.att", expected: "index.docker.io/library/image"},
-		{name: RegistryPrefix + "image:tag", expected: RegistryPrefix + "index.docker.io/library/image"},
+		{name: oci.RegistryPrefix + "image:tag", expected: oci.RegistryPrefix + "index.docker.io/library/image"},
 		{name: "image@sha256:166710df254975d4a6c4c407c315951c22753dcaa829e020a3fd5d18fff70dd2", expected: "index.docker.io/library/image"},
-		{name: RegistryPrefix + "image@sha256:166710df254975d4a6c4c407c315951c22753dcaa829e020a3fd5d18fff70dd2", expected: RegistryPrefix + "index.docker.io/library/image"},
-		{name: RegistryPrefix + "127.0.0.1:36555/repo:latest", expected: RegistryPrefix + "127.0.0.1:36555/repo"},
+		{name: oci.RegistryPrefix + "image@sha256:166710df254975d4a6c4c407c315951c22753dcaa829e020a3fd5d18fff70dd2", expected: oci.RegistryPrefix + "index.docker.io/library/image"},
+		{name: oci.RegistryPrefix + "127.0.0.1:36555/repo:latest", expected: oci.RegistryPrefix + "127.0.0.1:36555/repo"},
 	}
 	for _, c := range tc {
 		t.Run(c.name, func(t *testing.T) {
-			notag, _ := WithoutTag(c.name)
+			notag, _ := oci.WithoutTag(c.name)
 			assert.Equal(t, c.expected, notag)
 		})
 	}
@@ -116,11 +115,11 @@ func TestReplaceTag(t *testing.T) {
 		{name: "image:tag", expected: "index.docker.io/library/image:sha256-digest.att"},
 		{name: "image", expected: "index.docker.io/library/image:sha256-digest.att"},
 		{name: "image:sha256-digest.att", expected: "index.docker.io/library/image:sha256-digest.att"},
-		{name: RegistryPrefix + "image:tag", expected: RegistryPrefix + "index.docker.io/library/image:sha256-digest.att"},
+		{name: oci.RegistryPrefix + "image:tag", expected: oci.RegistryPrefix + "index.docker.io/library/image:sha256-digest.att"},
 		{name: "image@sha256:166710df254975d4a6c4c407c315951c22753dcaa829e020a3fd5d18fff70dd2", expected: "index.docker.io/library/image:sha256-digest.att"},
-		{name: LocalPrefix + "foobar", expected: LocalPrefix + "foobar"},
-		{name: RegistryPrefix + "image@sha256:166710df254975d4a6c4c407c315951c22753dcaa829e020a3fd5d18fff70dd2", expected: RegistryPrefix + "index.docker.io/library/image:sha256-digest.att"},
-		{name: RegistryPrefix + "127.0.0.1:36555/repo:latest", expected: RegistryPrefix + "127.0.0.1:36555/repo:sha256-digest.att"},
+		{name: oci.LocalPrefix + "foobar", expected: oci.LocalPrefix + "foobar"},
+		{name: oci.RegistryPrefix + "image@sha256:166710df254975d4a6c4c407c315951c22753dcaa829e020a3fd5d18fff70dd2", expected: oci.RegistryPrefix + "index.docker.io/library/image:sha256-digest.att"},
+		{name: oci.RegistryPrefix + "127.0.0.1:36555/repo:latest", expected: oci.RegistryPrefix + "127.0.0.1:36555/repo:sha256-digest.att"},
 	}
 
 	digest := v1.Hash{
@@ -129,7 +128,7 @@ func TestReplaceTag(t *testing.T) {
 	}
 	for _, c := range tc {
 		t.Run(c.name, func(t *testing.T) {
-			replaced, err := replaceTag(c.name, digest)
+			replaced, err := oci.ReplaceTag(c.name, digest)
 			require.NoError(t, err)
 			assert.Equal(t, c.expected, replaced)
 		})

pkg/oci/output.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"os"
 
-	"github.com/docker/attest/pkg/attestation"
 	"github.com/google/go-containerregistry/pkg/name"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/empty"
@@ -13,6 +12,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 )
 
+// PushImageToRegistry pushes an image to the registry with the specified name.
 func PushImageToRegistry(image v1.Image, imageName string) error {
 	ref, err := name.ParseReference(imageName)
 	if err != nil {
@@ -23,6 +23,7 @@ func PushImageToRegistry(image v1.Image, imageName string) error {
 	return remote.Write(ref, image, MultiKeychainOption())
 }
 
+// PushIndexToRegistry pushes an index to the registry with the specified name.
 func PushIndexToRegistry(index v1.ImageIndex, imageName string) error {
 	// Parse the index name
 	ref, err := name.ParseReference(imageName)
@@ -34,6 +35,7 @@ func PushIndexToRegistry(index v1.ImageIndex, imageName string) error {
 	return remote.WriteIndex(ref, index, MultiKeychainOption())
 }
 
+// SaveIndexAsOCILayout saves an image as an OCI layout to the specified path.
 func SaveImageAsOCILayout(image v1.Image, path string) error {
 	// Save the image to the local filesystem
 	err := os.MkdirAll(path, os.ModePerm)
@@ -48,6 +50,7 @@ func SaveImageAsOCILayout(image v1.Image, path string) error {
 	return l.AppendImage(image)
 }
 
+// SaveIndexAsOCILayout saves an index as an OCI layout to the specified path.
 func SaveIndexAsOCILayout(image v1.ImageIndex, path string) error {
 	// Save the index to the local filesystem
 	err := os.MkdirAll(path, os.ModePerm)
@@ -62,6 +65,7 @@ func SaveIndexAsOCILayout(image v1.ImageIndex, path string) error {
 	return nil
 }
 
+// SaveIndex saves an index to the specified outputs.
 func SaveIndex(outputs []*ImageSpec, index v1.ImageIndex, indexName string) error {
 	// split output by comma and write or push each one
 	for _, output := range outputs {
@@ -89,6 +93,7 @@ func SaveIndex(outputs []*ImageSpec, index v1.ImageIndex, indexName string) erro
 	return nil
 }
 
+// SaveImage saves an image to the specified output.
 func SaveImage(output *ImageSpec, image v1.Image, imageName string) error {
 	if output.Type == OCI {
 		idx := v1.ImageIndex(empty.Index)
@@ -113,26 +118,23 @@ func SaveImage(output *ImageSpec, image v1.Image, imageName string) error {
 	return nil
 }
 
-func SaveReferrers(manifest *attestation.Manifest, outputs []*ImageSpec) error {
+// SaveImagesNoTag saves a list of images by digest to the specified outputs.
+func SaveImagesNoTag(images []v1.Image, outputs []*ImageSpec) error {
 	for _, output := range outputs {
-		// OCI layout output for referrers not supported
+		// OCI layout output not supported
 		if output.Type == OCI {
 			continue
 		}
-		images, err := manifest.BuildReferringArtifacts()
-		if err != nil {
-			return fmt.Errorf("failed to build image: %w", err)
-		}
 		for _, image := range images {
 			digest, err := image.Digest()
 			if err != nil {
-				return fmt.Errorf("failed to get attestation image digest: %w", err)
+				return fmt.Errorf("failed to get image digest: %w", err)
 			}
-			attOut, err := ReplaceDigestInSpec(output, digest)
+			spec, err := ReplaceDigestInSpec(output, digest)
 			if err != nil {
-				return fmt.Errorf("failed to create attestation image spec: %w", err)
+				return fmt.Errorf("failed to create image spec: %w", err)
 			}
-			err = PushImageToRegistry(image, attOut.Identifier)
+			err = PushImageToRegistry(image, spec.Identifier)
 			if err != nil {
 				return fmt.Errorf("failed to push image: %w", err)
 			}

pkg/oci/output_test.go

@@ -4,11 +4,9 @@ import (
 	"fmt"
 	"net/http/httptest"
 	"net/url"
-	"path/filepath"
 	"testing"
 
 	"github.com/docker/attest/internal/test"
-	"github.com/docker/attest/pkg/attest"
 	"github.com/docker/attest/pkg/attestation"
 	"github.com/docker/attest/pkg/oci"
 	"github.com/google/go-containerregistry/pkg/registry"
@@ -19,9 +17,8 @@ import (
 )
 
 func TestSavingIndex(t *testing.T) {
-	UnsignedTestImage := filepath.Join("..", "..", "test", "testdata", "unsigned-test-image")
 	outputLayout := test.CreateTempDir(t, "", "mirror-test")
-	attIdx, err := oci.IndexFromPath(UnsignedTestImage)
+	attIdx, err := oci.IndexFromPath(test.UnsignedTestImage)
 	require.NoError(t, err)
 
 	server := httptest.NewServer(registry.New())
@@ -80,9 +77,9 @@ func TestSavingReferrers(t *testing.T) {
 		MediaType: "application/vnd.oci.image.manifest.v1+json",
 		Digest:    digest,
 	}
-	manifest, err := attest.NewAttestationManifest(subject)
+	manifest, err := attestation.NewManifest(subject)
 	require.NoError(t, err)
-	err = manifest.AddAttestation(ctx, signer, statement, opts)
+	err = manifest.Add(ctx, signer, statement, opts)
 	require.NoError(t, err)
 	server := httptest.NewServer(registry.New(registry.WithReferrersSupport(true)))
 	defer server.Close()
@@ -93,16 +90,18 @@ func TestSavingReferrers(t *testing.T) {
 	indexName := fmt.Sprintf("%s/repo:root", u.Host)
 	output, err := oci.ParseImageSpecs(indexName)
 	require.NoError(t, err)
-	err = oci.SaveReferrers(manifest, output)
+	artifacts, err := manifest.BuildReferringArtifacts()
+	require.NoError(t, err)
+	err = oci.SaveImagesNoTag(artifacts, output)
 	require.NoError(t, err)
 
-	reg := &oci.MockRegistryResolver{
+	reg := &attestation.MockRegistryResolver{
 		Subject:      subject,
-		MockResolver: &oci.MockResolver{},
+		MockResolver: &attestation.MockResolver{},
 		ImageNameStr: indexName,
 	}
 	require.NoError(t, err)
-	refResolver, err := oci.NewReferrersAttestationResolver(reg)
+	refResolver, err := attestation.NewReferrersResolver(reg)
 	require.NoError(t, err)
 	attestations, err := refResolver.Attestations(ctx, attestation.VSAPredicateType)
 	require.NoError(t, err)

pkg/oci/registry.go

@@ -4,18 +4,11 @@ import (
 	"context"
 	"fmt"
 
-	"github.com/docker/attest/pkg/attestation"
-	att "github.com/docker/attest/pkg/attestation"
 	"github.com/google/go-containerregistry/pkg/name"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 )
 
-type RegistryResolver struct {
-	*RegistryImageDetailsResolver
-	*attestation.Manifest
-}
-
 type RegistryImageDetailsResolver struct {
 	*ImageSpec
 	descriptor *v1.Descriptor
@@ -27,12 +20,6 @@ func NewRegistryImageDetailsResolver(src *ImageSpec) (*RegistryImageDetailsResol
 	}, nil
 }
 
-func NewRegistryAttestationResolver(src *RegistryImageDetailsResolver) (*RegistryResolver, error) {
-	return &RegistryResolver{
-		RegistryImageDetailsResolver: src,
-	}, nil
-}
-
 func (r *RegistryImageDetailsResolver) ImageName(_ context.Context) (string, error) {
 	return r.Identifier, nil
 }
@@ -72,70 +59,3 @@ func (r *RegistryImageDetailsResolver) ImageDescriptor(ctx context.Context) (*v1
 	}
 	return r.descriptor, nil
 }
-
-func (r *RegistryResolver) Attestations(ctx context.Context, predicateType string) ([]*att.Envelope, error) {
-	if r.Manifest == nil {
-		attest, err := FetchAttestationManifest(ctx, r.Identifier, r.ImageSpec.Platform)
-		if err != nil {
-			return nil, err
-		}
-		r.Manifest = attest
-	}
-	return ExtractEnvelopes(r.Manifest, predicateType)
-}
-
-func FetchAttestationManifest(ctx context.Context, image string, platform *v1.Platform) (*attestation.Manifest, error) {
-	// we want to get to the image index, so ignoring platform for now
-	options := WithOptions(ctx, nil)
-	ref, err := name.ParseReference(image)
-	if err != nil {
-		return nil, fmt.Errorf("failed to parse reference: %w", err)
-	}
-	index, err := remote.Index(ref, options...)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get index: %w", err)
-	}
-	indexManifest, err := index.IndexManifest()
-	if err != nil {
-		return nil, fmt.Errorf("failed to get index manifest: %w", err)
-	}
-	subjectDescriptor, err := imageDescriptor(indexManifest, platform)
-	if err != nil {
-		return nil, fmt.Errorf("failed to obtain image for platform: %w", err)
-	}
-
-	digest := subjectDescriptor.Digest.String()
-	ref, err = name.ParseReference(fmt.Sprintf("%s@%s", ref.Context().Name(), digest))
-	if err != nil {
-		return nil, fmt.Errorf("failed to parse attestation reference: %w", err)
-	}
-
-	attestationDigest, err := attestationDigestForDigest(indexManifest, digest, "attestation-manifest")
-	if err != nil {
-		return nil, fmt.Errorf("failed to obtain attestation for image: %w", err)
-	}
-	ref, err = name.ParseReference(fmt.Sprintf("%s@%s", ref.Context().Name(), attestationDigest))
-	if err != nil {
-		return nil, fmt.Errorf("failed to parse attestation reference: %w", err)
-	}
-	remoteDescriptor, err := remote.Get(ref, options...)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get attestation: %w", err)
-	}
-	attestationImage, err := remoteDescriptor.Image()
-	if err != nil {
-		return nil, fmt.Errorf("failed to get attestation image: %w", err)
-	}
-
-	layers, err := attestation.GetAttestationsFromImage(attestationImage)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get attestations from image: %w", err)
-	}
-	attest := &attestation.Manifest{
-		OriginalLayers:     layers,
-		OriginalDescriptor: &remoteDescriptor.Descriptor,
-		SubjectName:        image,
-		SubjectDescriptor:  subjectDescriptor,
-	}
-	return attest, nil
-}

pkg/oci/resolver.go

@@ -3,15 +3,9 @@ package oci
 import (
 	"context"
 
-	att "github.com/docker/attest/pkg/attestation"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 )
 
-type AttestationResolver interface {
-	ImageDetailsResolver
-	Attestations(ctx context.Context, mediaType string) ([]*att.Envelope, error)
-}
-
 type ImageDetailsResolver interface {
 	ImageName(ctx context.Context) (string, error)
 	ImagePlatform(ctx context.Context) (*v1.Platform, error)

pkg/oci/types.go

@@ -1,6 +1,8 @@
 package oci
 
 import (
+	"bytes"
+	"encoding/json"
 	"fmt"
 	"strings"
 
@@ -26,12 +28,6 @@ type (
 	}
 )
 
-type AttestationOptions struct {
-	NoReferrers   bool
-	Attach        bool
-	ReferrersRepo string
-}
-
 type ImageSpecOption func(*ImageSpec) error
 
 type ImageSpec struct {
@@ -180,3 +176,42 @@ func WithoutTag(image string) (string, error) {
 	repo := ref.Context().Name()
 	return prefix + repo, nil
 }
+
+type EmptyConfigImage struct {
+	v1.Image
+}
+
+func (i *EmptyConfigImage) RawConfigFile() ([]byte, error) {
+	return []byte("{}"), nil
+}
+
+func (i *EmptyConfigImage) Manifest() (*v1.Manifest, error) {
+	mf, err := i.Image.Manifest()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get manifest: %w", err)
+	}
+	mf.Config = v1.Descriptor{
+		MediaType: "application/vnd.oci.empty.v1+json",
+		Size:      2,
+		Digest:    v1.Hash{Algorithm: "sha256", Hex: "44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a"},
+		Data:      []byte("{}"),
+	}
+	return mf, nil
+}
+
+func (i *EmptyConfigImage) RawManifest() ([]byte, error) {
+	mf, err := i.Manifest()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get manifest: %w", err)
+	}
+	return json.Marshal(mf)
+}
+
+func (i *EmptyConfigImage) Digest() (v1.Hash, error) {
+	mb, err := i.RawManifest()
+	if err != nil {
+		return v1.Hash{}, err
+	}
+	digest, _, err := v1.SHA256(bytes.NewReader(mb))
+	return digest, err
+}

pkg/oci/types_test.go

@@ -0,0 +1,21 @@
+package oci
+
+import (
+	"testing"
+
+	"github.com/docker/attest/internal/util"
+	"github.com/google/go-containerregistry/pkg/v1/empty"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEmptyConfigImageDigest(t *testing.T) {
+	empty := empty.Image
+	img := EmptyConfigImage{Image: empty}
+	mf, err := img.RawManifest()
+	require.NoError(t, err)
+	hash := util.SHA256Hex(mf)
+	digest, err := img.Digest()
+	require.NoError(t, err)
+	assert.Equal(t, digest.Hex, hash)
+}

pkg/policy/README.md

@@ -0,0 +1,2 @@
+## policy
+This package is for attestation policy mapping and evaluation.

pkg/policy/evaluator.go

@@ -4,7 +4,7 @@ import (
 	"context"
 	"fmt"
 
-	"github.com/docker/attest/pkg/oci"
+	"github.com/docker/attest/pkg/attestation"
 )
 
 type policyEvaluatorCtxKeyType struct{}
@@ -26,5 +26,5 @@ func GetPolicyEvaluator(ctx context.Context) (Evaluator, error) {
 }
 
 type Evaluator interface {
-	Evaluate(ctx context.Context, resolver oci.AttestationResolver, pctx *Policy, input *Input) (*Result, error)
+	Evaluate(ctx context.Context, resolver attestation.Resolver, pctx *Policy, input *Input) (*Result, error)
 }

pkg/policy/mock.go

@@ -3,14 +3,14 @@ package policy
 import (
 	"context"
 
-	"github.com/docker/attest/pkg/oci"
+	"github.com/docker/attest/pkg/attestation"
 )
 
 type MockPolicyEvaluator struct {
-	EvaluateFunc func(ctx context.Context, resolver oci.AttestationResolver, pctx *Policy, input *Input) (*Result, error)
+	EvaluateFunc func(ctx context.Context, resolver attestation.Resolver, pctx *Policy, input *Input) (*Result, error)
 }
 
-func (pe *MockPolicyEvaluator) Evaluate(ctx context.Context, resolver oci.AttestationResolver, pctx *Policy, input *Input) (*Result, error) {
+func (pe *MockPolicyEvaluator) Evaluate(ctx context.Context, resolver attestation.Resolver, pctx *Policy, input *Input) (*Result, error) {
 	if pe.EvaluateFunc != nil {
 		return pe.EvaluateFunc(ctx, resolver, pctx, input)
 	}
@@ -19,7 +19,7 @@ func (pe *MockPolicyEvaluator) Evaluate(ctx context.Context, resolver oci.Attest
 
 func GetMockPolicy() Evaluator {
 	return &MockPolicyEvaluator{
-		EvaluateFunc: func(_ context.Context, _ oci.AttestationResolver, _ *Policy, _ *Input) (*Result, error) {
+		EvaluateFunc: func(_ context.Context, _ attestation.Resolver, _ *Policy, _ *Input) (*Result, error) {
 			return AllowedResult(), nil
 		},
 	}

pkg/policy/policy.go

@@ -8,6 +8,8 @@ import (
 	"path/filepath"
 
 	"github.com/distribution/reference"
+	"github.com/docker/attest/internal/util"
+	"github.com/docker/attest/pkg/attestation"
 	"github.com/docker/attest/pkg/config"
 	"github.com/docker/attest/pkg/oci"
 )
@@ -16,6 +18,8 @@ func resolveLocalPolicy(opts *Options, mapping *config.PolicyMapping, imageName
 	if opts.LocalPolicyDir == "" {
 		return nil, fmt.Errorf("local policy dir not set")
 	}
+	var URI string
+	var digest map[string]string
 	files := make([]*File, 0, len(mapping.Files))
 	for _, f := range mapping.Files {
 		filename := f.Path
@@ -28,10 +32,24 @@ func resolveLocalPolicy(opts *Options, mapping *config.PolicyMapping, imageName
 			Path:    filename,
 			Content: fileContents,
 		})
+		// if the file is a policy file, store the URI and digest
+		if filepath.Ext(filename) == ".rego" {
+			// TODO: support multiple rego files, need some way to identify the main policy file
+			if URI != "" {
+				return nil, fmt.Errorf("multiple policy files found in policy mapping")
+			}
+			URI = filePath
+			digest = map[string]string{"sha256": util.SHA256Hex(fileContents)}
+		}
+	}
+	if URI == "" {
+		return nil, fmt.Errorf("no policy file found in policy mapping")
 	}
 	policy := &Policy{
 		InputFiles: files,
 		Mapping:    mapping,
+		URI:        URI,
+		Digest:     digest,
 	}
 	if imageName != matchedName {
 		policy.ResolvedName = matchedName
@@ -40,21 +58,37 @@ func resolveLocalPolicy(opts *Options, mapping *config.PolicyMapping, imageName
 }
 
 func resolveTUFPolicy(opts *Options, mapping *config.PolicyMapping, imageName string, matchedName string) (*Policy, error) {
+	var URI string
+	var digest map[string]string
 	files := make([]*File, 0, len(mapping.Files))
 	for _, f := range mapping.Files {
 		filename := f.Path
-		_, fileContents, err := opts.TUFClient.DownloadTarget(filename, filepath.Join(opts.LocalTargetsDir, filename))
+		file, err := opts.TUFClient.DownloadTarget(filename, filepath.Join(opts.LocalTargetsDir, filename))
 		if err != nil {
 			return nil, fmt.Errorf("failed to download policy file %s: %w", filename, err)
 		}
 		files = append(files, &File{
 			Path:    filename,
-			Content: fileContents,
+			Content: file.Data,
 		})
+		// if the file is a policy file, store the URI and digest
+		if filepath.Ext(filename) == ".rego" {
+			// TODO: support multiple rego files, need some way to identify the main policy file
+			if URI != "" {
+				return nil, fmt.Errorf("multiple policy files found in policy mapping")
+			}
+			URI = file.TargetURI
+			digest = map[string]string{"sha256": file.Digest}
+		}
+	}
+	if URI == "" {
+		return nil, fmt.Errorf("no policy file found in policy mapping")
 	}
 	policy := &Policy{
 		InputFiles: files,
 		Mapping:    mapping,
+		URI:        URI,
+		Digest:     digest,
 	}
 	if imageName != matchedName {
 		policy.ResolvedName = matchedName
@@ -211,28 +245,28 @@ func normalizeImageName(imageName string) (string, error) {
 func CreateImageDetailsResolver(imageSource *oci.ImageSpec) (oci.ImageDetailsResolver, error) {
 	switch imageSource.Type {
 	case oci.OCI:
-		return oci.NewOCILayoutAttestationResolver(imageSource)
+		return attestation.NewOCILayoutResolver(imageSource)
 	case oci.Docker:
 		return oci.NewRegistryImageDetailsResolver(imageSource)
 	}
 	return nil, fmt.Errorf("unsupported image source type: %s", imageSource.Type)
 }
 
-func CreateAttestationResolver(resolver oci.ImageDetailsResolver, mapping *config.PolicyMapping) (oci.AttestationResolver, error) {
+func CreateAttestationResolver(resolver oci.ImageDetailsResolver, mapping *config.PolicyMapping) (attestation.Resolver, error) {
 	if mapping.Attestations != nil {
 		if mapping.Attestations.Style == config.AttestationStyleAttached {
 			switch resolver := resolver.(type) {
 			case *oci.RegistryImageDetailsResolver:
-				return oci.NewRegistryAttestationResolver(resolver)
-			case *oci.LayoutResolver:
+				return attestation.NewRegistryResolver(resolver)
+			case *attestation.LayoutResolver:
 				return resolver, nil
 			default:
 				return nil, fmt.Errorf("unsupported image details resolver type: %T", resolver)
 			}
 		}
 		if mapping.Attestations.Repo != "" {
-			return oci.NewReferrersAttestationResolver(resolver, oci.WithReferrersRepo(mapping.Attestations.Repo))
+			return attestation.NewReferrersResolver(resolver, attestation.WithReferrersRepo(mapping.Attestations.Repo))
 		}
 	}
-	return oci.NewReferrersAttestationResolver(resolver)
+	return attestation.NewReferrersResolver(resolver)
 }

pkg/policy/policy_test.go

@@ -32,33 +32,34 @@ func loadAttestation(t *testing.T, path string) *attestation.Envelope {
 
 func TestRegoEvaluator_Evaluate(t *testing.T) {
 	ctx, _ := test.Setup(t)
-	errorStr := "failed to resolve policy by id: policy with id non-existent-policy-id not found"
+	resolveErrorStr := "failed to resolve policy by id: policy with id non-existent-policy-id not found"
 	TestDataPath := filepath.Join("..", "..", "test", "testdata")
 	ExampleAttestation := filepath.Join(TestDataPath, "example_attestation.json")
 
 	re := policy.NewRegoEvaluator(true)
 
-	defaultResolver := oci.MockResolver{
+	defaultResolver := attestation.MockResolver{
 		Envs: []*attestation.Envelope{loadAttestation(t, ExampleAttestation)},
 	}
 
 	testCases := []struct {
-		repo          string
-		expectSuccess bool
-		isCanonical   bool
-		resolver      oci.AttestationResolver
-		policy        *policy.Options
-		policyID      string
-		errorStr      string
+		repo            string
+		expectSuccess   bool
+		isCanonical     bool
+		resolver        attestation.Resolver
+		policy          *policy.Options
+		policyID        string
+		resolveErrorStr string
 	}{
 		{repo: "testdata/mock-tuf-allow", expectSuccess: true, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-allow", expectSuccess: true, isCanonical: false, resolver: defaultResolver, policyID: "docker-official-images"},
-		{repo: "testdata/mock-tuf-allow", expectSuccess: false, isCanonical: false, resolver: defaultResolver, policyID: "non-existent-policy-id", errorStr: errorStr},
+		{repo: "testdata/mock-tuf-allow", expectSuccess: false, isCanonical: false, resolver: defaultResolver, policyID: "non-existent-policy-id", resolveErrorStr: resolveErrorStr},
 		{repo: "testdata/mock-tuf-deny", expectSuccess: false, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-verify-sig", expectSuccess: true, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-wrong-key", expectSuccess: false, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-allow-canonical", expectSuccess: true, isCanonical: true, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-allow-canonical", expectSuccess: false, isCanonical: false, resolver: defaultResolver},
+		{repo: "testdata/mock-tuf-no-rego", expectSuccess: false, isCanonical: false, resolver: defaultResolver, resolveErrorStr: "no policy file found in policy mapping"},
 	}
 
 	for _, tc := range testCases {
@@ -86,9 +87,9 @@ func TestRegoEvaluator_Evaluate(t *testing.T) {
 			resolver, err := policy.CreateImageDetailsResolver(src)
 			require.NoError(t, err)
 			policy, err := policy.ResolvePolicy(ctx, resolver, tc.policy)
-			if tc.errorStr != "" {
+			if tc.resolveErrorStr != "" {
 				require.Error(t, err)
-				assert.Contains(t, err.Error(), tc.errorStr)
+				assert.Contains(t, err.Error(), tc.resolveErrorStr)
 				return
 			}
 			require.NoErrorf(t, err, "failed to resolve policy")
@@ -117,10 +118,10 @@ func TestLoadingMappings(t *testing.T) {
 }
 
 func TestCreateAttestationResolver(t *testing.T) {
-	mockResolver := oci.MockResolver{
+	mockResolver := attestation.MockResolver{
 		Envs: []*attestation.Envelope{},
 	}
-	layoutResolver := &oci.LayoutResolver{}
+	layoutResolver := &attestation.LayoutResolver{}
 	registryResolver := &oci.RegistryImageDetailsResolver{}
 
 	nilRepoReferrers := &config.PolicyMapping{
@@ -166,11 +167,11 @@ func TestCreateAttestationResolver(t *testing.T) {
 				return
 			}
 			switch resolver.(type) {
-			case *oci.ReferrersResolver:
+			case *attestation.ReferrersResolver:
 				assert.Equal(t, tc.mapping.Attestations.Style, config.AttestationStyleReferrers)
-			case *oci.RegistryResolver:
+			case *attestation.RegistryResolver:
 				assert.Equal(t, tc.mapping.Attestations.Style, config.AttestationStyleAttached)
-			case *oci.LayoutResolver:
+			case *attestation.LayoutResolver:
 				assert.Equal(t, tc.mapping.Attestations.Style, config.AttestationStyleAttached)
 			}
 		})

pkg/policy/rego.go

@@ -7,8 +7,7 @@ import (
 	"os"
 	"path/filepath"
 
-	att "github.com/docker/attest/pkg/attestation"
-	"github.com/docker/attest/pkg/oci"
+	"github.com/docker/attest/pkg/attestation"
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
 	"github.com/open-policy-agent/opa/ast"
 	"github.com/open-policy-agent/opa/rego"
@@ -36,7 +35,7 @@ func NewRegoEvaluator(debug bool) Evaluator {
 	}
 }
 
-func (re *regoEvaluator) Evaluate(ctx context.Context, resolver oci.AttestationResolver, pctx *Policy, input *Input) (*Result, error) {
+func (re *regoEvaluator) Evaluate(ctx context.Context, resolver attestation.Resolver, pctx *Policy, input *Input) (*Result, error) {
 	var regoOpts []func(*rego.Rego)
 
 	// Create a new in-memory store
@@ -170,7 +169,7 @@ func handleErrors2(f func(rCtx *rego.BuiltinContext, a, b *ast.Term) (*ast.Term,
 	}
 }
 
-func RegoFunctions(resolver oci.AttestationResolver) []*tester.Builtin {
+func RegoFunctions(resolver attestation.Resolver) []*tester.Builtin {
 	return []*tester.Builtin{
 		{
 			Decl: verifyDecl,
@@ -197,7 +196,7 @@ func RegoFunctions(resolver oci.AttestationResolver) []*tester.Builtin {
 	}
 }
 
-func fetchInTotoAttestations(resolver oci.AttestationResolver) rego.Builtin1 {
+func fetchInTotoAttestations(resolver attestation.Resolver) rego.Builtin1 {
 	return func(rCtx rego.BuiltinContext, predicateTypeTerm *ast.Term) (*ast.Term, error) {
 		predicateTypeStr, ok := predicateTypeTerm.Value.(ast.String)
 		if !ok {
@@ -228,8 +227,8 @@ func fetchInTotoAttestations(resolver oci.AttestationResolver) rego.Builtin1 {
 }
 
 func verifyInTotoEnvelope(rCtx *rego.BuiltinContext, envTerm, optsTerm *ast.Term) (*ast.Term, error) {
-	env := new(att.Envelope)
-	opts := new(att.VerifyOptions)
+	env := new(attestation.Envelope)
+	opts := new(attestation.VerifyOptions)
 	err := ast.As(envTerm.Value, env)
 	if err != nil {
 		return nil, fmt.Errorf("failed to cast envelope: %w", err)
@@ -239,7 +238,7 @@ func verifyInTotoEnvelope(rCtx *rego.BuiltinContext, envTerm, optsTerm *ast.Term
 		return nil, fmt.Errorf("failed to cast verifier options: %w", err)
 	}
 
-	payload, err := att.VerifyDSSE(rCtx.Context, env, opts)
+	payload, err := attestation.VerifyDSSE(rCtx.Context, env, opts)
 	if err != nil {
 		return nil, err
 	}

pkg/policy/testdata/mock-tuf-no-rego/doi/policy.yaml

@@ -0,0 +1 @@
+policy: "this is not rego"

pkg/policy/testdata/mock-tuf-no-rego/mapping.yaml

@@ -0,0 +1,11 @@
+# map repos to policies
+version: v1
+kind: policy-mapping
+policies:
+  - id: docker-official-images
+    description: Docker Official Images
+    files:
+      - path: doi/policy.yaml
+rules:
+  - pattern: "^docker[.]io/library/(.*)$"
+    policy-id: docker-official-images

pkg/policy/types.go

@@ -40,6 +40,8 @@ type Policy struct {
 	Query        string
 	Mapping      *config.PolicyMapping
 	ResolvedName string
+	URI          string
+	Digest       map[string]string
 }
 
 type Input struct {

pkg/signerverifier/README.md

@@ -0,0 +1,2 @@
+## signerverifier
+This package implements methods to sign and verify attestation envelopes.

pkg/tlog/README.md

@@ -0,0 +1,2 @@
+## tlog
+This package implements transparency logging.

pkg/tuf/README.md

@@ -0,0 +1,2 @@
+## tuf
+This package implements TUF clients for http and oci data sources.

pkg/tuf/example_registry_test.go

@@ -28,16 +28,13 @@ func ExampleNewClient_registry() {
 
 	// get trusted tuf metadata
 	trustedMetadata := registryClient.GetMetadata()
-	if err != nil {
-		panic(err)
-	}
 
 	// top-level target files
 	targets := trustedMetadata.Targets[metadata.TARGETS].Signed.Targets
 
 	for _, t := range targets {
 		// download target files
-		_, _, err := registryClient.DownloadTarget(t.Path, filepath.Join(tufOutputPath, "download"))
+		_, err := registryClient.DownloadTarget(t.Path, filepath.Join(tufOutputPath, "download"))
 		if err != nil {
 			panic(err)
 		}

pkg/tuf/mock.go

@@ -4,6 +4,8 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+
+	"github.com/docker/attest/internal/util"
 )
 
 type MockTufClient struct {
@@ -24,10 +26,11 @@ func NewMockTufClient(srcPath string, dstPath string) *MockTufClient {
 	}
 }
 
-func (dc *MockTufClient) DownloadTarget(target string, filePath string) (actualFilePath string, data []byte, err error) {
-	src, err := os.Open(filepath.Join(dc.srcPath, target))
+func (dc *MockTufClient) DownloadTarget(target string, filePath string) (file *TargetFile, err error) {
+	targetPath := filepath.Join(dc.srcPath, target)
+	src, err := os.Open(targetPath)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 	defer src.Close()
 
@@ -40,11 +43,11 @@ func (dc *MockTufClient) DownloadTarget(target string, filePath string) (actualF
 
 	err = os.MkdirAll(filepath.Dir(dstFilePath), os.ModePerm)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 	dst, err := os.Create(dstFilePath)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 	defer dst.Close()
 
@@ -53,10 +56,10 @@ func (dc *MockTufClient) DownloadTarget(target string, filePath string) (actualF
 
 	b, err := io.ReadAll(tee)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 
-	return dstFilePath, b, nil
+	return &TargetFile{ActualFilePath: dstFilePath, TargetURI: targetPath, Data: b, Digest: util.SHA256Hex(b)}, nil
 }
 
 type MockVersionChecker struct {

pkg/tuf/registry_test.go

@@ -32,6 +32,9 @@ const (
 	tufTargetMediaType = "application/vnd.tuf.target"
 	testRole           = "test-role"
 	tufMetadataRepo    = "tuf-metadata"
+	targetsPath        = "/tuf-targets"
+	metadataPath       = "/tuf-metadata"
+	targetsRepo        = "test" + targetsPath
 )
 
 func TestRegistryFetcher(t *testing.T) {
@@ -44,9 +47,9 @@ func TestRegistryFetcher(t *testing.T) {
 	}()
 	LoadRegistryTestData(t, regAddr, OCITUFTestDataPath)
 
-	metadataRepo := regAddr.Host + "/tuf-metadata"
+	metadataRepo := regAddr.Host + metadataPath
 	metadataImgTag := LatestTag
-	targetsRepo := regAddr.Host + "/tuf-targets"
+	targetsRepo := regAddr.Host + targetsPath
 	targetFile := "test.txt"
 	delegatedRole := testRole
 	dir := CreateTempDir(t, "", "tuf_temp")
@@ -122,7 +125,7 @@ func TestFindFileInManifest(t *testing.T) {
 	// make test image manifest
 	file := "test.json"
 	data := []byte("test")
-	hash := v1.Hash{Algorithm: "sha256", Hex: util.SHA256Hex(data)}
+	hash := v1.Hash{Hex: util.SHA256Hex(data)}
 	img := empty.Image
 	img = mutate.MediaType(img, types.OCIManifestSchema1)
 	img = mutate.ConfigMediaType(img, types.OCIConfigJSON)
@@ -150,7 +153,6 @@ func TestFindFileInManifest(t *testing.T) {
 	indexManifest, err := idx.RawManifest()
 	assert.NoError(t, err)
 	// cache image layer
-	targetsRepo := "test/tuf-targets"
 	d := &RegistryFetcher{
 		cache:       NewImageCache(),
 		targetsRepo: targetsRepo,
@@ -183,9 +185,8 @@ func TestFindFileInManifest(t *testing.T) {
 }
 
 func TestParseImgRef(t *testing.T) {
-	metadataRepo := "test/tuf-metadata"
+	metadataRepo := "test" + metadataPath
 	metadataTag := LatestTag
-	targetsRepo := "test/tuf-targets"
 	delegatedRole := testRole
 	testCases := []struct {
 		name         string

pkg/tuf/tuf.go

@@ -36,7 +36,7 @@ var (
 )
 
 type Downloader interface {
-	DownloadTarget(target, filePath string) (actualFilePath string, data []byte, err error)
+	DownloadTarget(target, filePath string) (file *TargetFile, err error)
 }
 
 type Client struct {
@@ -44,6 +44,13 @@ type Client struct {
 	cfg     *config.UpdaterConfig
 }
 
+type TargetFile struct {
+	ActualFilePath string
+	TargetURI      string
+	Digest         string
+	Data           []byte
+}
+
 // NewClient creates a new TUF client.
 func NewClient(initialRoot []byte, tufPath, metadataSource, targetsSource string, versionChecker VersionChecker) (*Client, error) {
 	var tufSource Source
@@ -119,40 +126,69 @@ func NewClient(initialRoot []byte, tufPath, metadataSource, targetsSource string
 	return client, nil
 }
 
+func (t *Client) generateTargetURI(target *metadata.TargetFiles, digest string) (string, error) {
+	switch fetcher := t.cfg.Fetcher.(type) {
+	case *RegistryFetcher:
+		return fmt.Sprintf("%s@sha256:%s", t.cfg.RemoteTargetsURL, digest), nil
+	case *fetcher.DefaultFetcher:
+		targetBaseURL := ensureTrailingSlash(t.cfg.RemoteTargetsURL)
+		targetRemotePath := target.Path
+		// if PrefixTargetsWithHash is set, we need to prefix the target name with the hash and handle subdirectories
+		// similar logic to https://github.com/theupdateframework/go-tuf/blob/f95222bdd22d2ac4e5b8ed6fe912b645e213c3b5/metadata/updater/updater.go#L227-L247
+		if t.cfg.PrefixTargetsWithHash {
+			baseName := filepath.Base(targetRemotePath)
+			dirName, ok := strings.CutSuffix(targetRemotePath, "/"+baseName)
+			if !ok {
+				// <hash>.<target-name>
+				targetRemotePath = fmt.Sprintf("%s.%s", digest, baseName)
+			} else {
+				// <dir-prefix>/<hash>.<target-name>
+				targetRemotePath = fmt.Sprintf("%s/%s.%s", dirName, digest, baseName)
+			}
+		}
+		return fmt.Sprintf("%s%s", targetBaseURL, targetRemotePath), nil
+	default:
+		return "", fmt.Errorf("unsupported fetcher type: %T", fetcher)
+	}
+}
+
 // DownloadTarget downloads the target file using Updater. The Updater gets the target
 // information, verifies if the target is already cached, and if it is not cached,
 // downloads the target file.
-func (t *Client) DownloadTarget(target string, filePath string) (actualFilePath string, data []byte, err error) {
+func (t *Client) DownloadTarget(target string, filePath string) (file *TargetFile, err error) {
 	// search if the desired target is available
 	targetInfo, err := t.updater.GetTargetInfo(target)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 
 	// check if filePath exists and create the directory if it doesn't
 	if _, err := os.Stat(filepath.Dir(filePath)); os.IsNotExist(err) {
 		err = os.MkdirAll(filepath.Dir(filePath), os.ModePerm)
 		if err != nil {
-			return "", nil, fmt.Errorf("failed to create target download directory '%s': %w", filepath.Dir(filePath), err)
+			return nil, fmt.Errorf("failed to create target download directory '%s': %w", filepath.Dir(filePath), err)
 		}
 	}
 
 	// target is available, so let's see if the target is already present locally
-	actualFilePath, data, err = t.updater.FindCachedTarget(targetInfo, filePath)
+	actualFilePath, data, err := t.updater.FindCachedTarget(targetInfo, filePath)
 	if err != nil {
-		return "", nil, fmt.Errorf("failed while finding a cached target: %w", err)
+		return nil, fmt.Errorf("failed while finding a cached target: %w", err)
 	}
 	if data != nil {
-		return actualFilePath, data, err
+		digest := util.SHA256Hex(data)
+		uri, err := t.generateTargetURI(targetInfo, digest)
+		return &TargetFile{ActualFilePath: actualFilePath, TargetURI: uri, Data: data, Digest: digest}, err
 	}
 
 	// target is not present locally, so let's try to download it
 	actualFilePath, data, err = t.updater.DownloadTarget(targetInfo, filePath, "")
 	if err != nil {
-		return "", nil, fmt.Errorf("failed to download target file %s - %w", target, err)
+		return nil, fmt.Errorf("failed to download target file %s - %w", target, err)
 	}
-
-	return actualFilePath, data, err
+	digest := util.SHA256Hex(data)
+	uri, err := t.generateTargetURI(targetInfo, digest)
+	return &TargetFile{ActualFilePath: actualFilePath, TargetURI: uri, Data: data, Digest: digest}, err
 }
 
 func (t *Client) GetMetadata() trustedmetadata.TrustedMetadata {

pkg/tuf/tuf_test.go

@@ -122,14 +122,14 @@ func TestDownloadTarget(t *testing.T) {
 		targets := trustedMetadata.Targets[metadata.TARGETS].Signed.Targets
 		for _, target := range targets {
 			// download target files
-			_, _, err := tufClient.DownloadTarget(target.Path, filepath.Join(tufPath, "download"))
+			_, err := tufClient.DownloadTarget(target.Path, filepath.Join(tufPath, "download"))
 			assert.NoErrorf(t, err, "Failed to download target: %v", err)
 		}
 
 		// download delegated target
 		targetInfo, err := tufClient.updater.GetTargetInfo(delegatedTargetFile)
 		assert.NoError(t, err)
-		_, _, err = tufClient.DownloadTarget(targetInfo.Path, filepath.Join(tufPath, targetInfo.Path))
+		_, err = tufClient.DownloadTarget(targetInfo.Path, filepath.Join(tufPath, targetInfo.Path))
 		assert.NoError(t, err)
 	}
 }

pkg/tuf/version.go

@@ -67,11 +67,11 @@ func (vc *DefaultVersionChecker) CheckVersion(client Downloader) error {
 
 	// see https://github.com/Masterminds/semver/blob/v3.2.1/README.md#checking-version-constraints
 	// for more information on the expected format of the version constraints in the TUF repo
-	_, versionConstraintsBytes, err := client.DownloadTarget("version-constraints", "")
+	target, err := client.DownloadTarget("version-constraints", "")
 	if err != nil {
 		return fmt.Errorf("failed to download version-constraints: %w", err)
 	}
-	versionConstraints, err := semver.NewConstraint(string(versionConstraintsBytes))
+	versionConstraints, err := semver.NewConstraint(string(target.Data))
 	if err != nil {
 		return fmt.Errorf("failed to parse minimum version: %w", err)
 	}

scripts/README.md

@@ -0,0 +1,4 @@
+## scripts
+This directory contains project scripts.
+
+`gen-testdata.sh` - used to generate static test data saved in `/test/testdata/`

test/README.md

@@ -0,0 +1,2 @@
+## test
+This directory contains static `testdata` used to run go tests.