Simplify and rename hash functions

pkg/signerverifier/common.go

@@ -38,7 +38,7 @@ func (s *ECDSA256_SignerVerifier) Verify(ctx context.Context, data []byte, sig [
 	if !ok {
 		return fmt.Errorf("public key is not ecdsa")
 	}
-	ok = ecdsa.VerifyASN1(pub, util.S256(data), sig)
+	ok = ecdsa.VerifyASN1(pub, util.SHA256(data), sig)
 	if !ok {
 		return fmt.Errorf("payload signature is not valid")
 	}

pkg/signerverifier/keyid.go

@@ -13,5 +13,5 @@ func KeyID(pubKey crypto.PublicKey) (string, error) {
 	if err != nil {
 		return "", fmt.Errorf("error marshalling public key: %w", err)
 	}
-	return util.HexHashBytes(pub), nil
+	return util.SHA256Hex(pub), nil
 }