feat: export the PluginPrimitiveSigner to enable signing with PKCS#7

signer/plugin.go

@@ -162,7 +162,7 @@ func (s *PluginSigner) generateSignature(ctx context.Context, desc ocispec.Descr
 	logger := log.GetLogger(ctx)
 	logger.Debug("Generating signature by plugin")
 	genericSigner := GenericSigner{
-		signer: &pluginPrimitiveSigner{
+		signer: &PluginPrimitiveSigner{
 			ctx:          ctx,
 			plugin:       s.plugin,
 			keyID:        s.keyID,
@@ -325,8 +325,8 @@ func parseCertChain(certChain [][]byte) ([]*x509.Certificate, error) {
 	return certs, nil
 }
 
-// pluginPrimitiveSigner implements signature.Signer
-type pluginPrimitiveSigner struct {
+// PluginPrimitiveSigner implements signature.Signer
+type PluginPrimitiveSigner struct {
 	ctx          context.Context
 	plugin       plugin.SignPlugin
 	keyID        string
@@ -335,7 +335,7 @@ type pluginPrimitiveSigner struct {
 }
 
 // Sign signs the digest by calling the underlying plugin.
-func (s *pluginPrimitiveSigner) Sign(payload []byte) ([]byte, []*x509.Certificate, error) {
+func (s *PluginPrimitiveSigner) Sign(payload []byte) ([]byte, []*x509.Certificate, error) {
 	// Execute plugin sign command.
 	keySpec, err := proto.EncodeKeySpec(s.keySpec)
 	if err != nil {
@@ -372,6 +372,35 @@ func (s *pluginPrimitiveSigner) Sign(payload []byte) ([]byte, []*x509.Certificat
 
 // KeySpec returns the keySpec of a keyID by calling describeKey and do some
 // keySpec validation.
-func (s *pluginPrimitiveSigner) KeySpec() (signature.KeySpec, error) {
+func (s *PluginPrimitiveSigner) KeySpec() (signature.KeySpec, error) {
 	return s.keySpec, nil
 }
+
+// NewPluginPrimitiveSigner creates a new PluginPrimitiveSigner that delegates
+// signing to a plugin. This is used for dm-verity PKCS#7 signing where raw
+// signature bytes are needed instead of JWS/COSE envelopes.
+func NewPluginPrimitiveSigner(ctx context.Context, p plugin.SignPlugin, keyID string, keySpec signature.KeySpec, pluginConfig map[string]string) *PluginPrimitiveSigner {
+	return &PluginPrimitiveSigner{
+		ctx:          ctx,
+		plugin:       p,
+		keyID:        keyID,
+		keySpec:      keySpec,
+		pluginConfig: pluginConfig,
+	}
+}
+
+// GetKeySpecFromPlugin retrieves the key specification from a plugin by calling DescribeKey.
+func GetKeySpecFromPlugin(ctx context.Context, p plugin.SignPlugin, keyID string, pluginConfig map[string]string) (signature.KeySpec, error) {
+	req := &plugin.DescribeKeyRequest{
+		ContractVersion: plugin.ContractVersion,
+		KeyID:           keyID,
+		PluginConfig:    pluginConfig,
+	}
+
+	resp, err := p.DescribeKey(ctx, req)
+	if err != nil {
+		return signature.KeySpec{}, err
+	}
+
+	return proto.DecodeKeySpec(resp.KeySpec)
+}

signer/plugin_test.go

@@ -166,7 +166,7 @@ func (p *mockPlugin) GenerateEnvelope(ctx context.Context, req *proto.GenerateEn
 			return nil, err
 		}
 
-		primitivePluginSigner := &pluginPrimitiveSigner{
+		primitivePluginSigner := &PluginPrimitiveSigner{
 			ctx:          ctx,
 			plugin:       internalPluginSigner.plugin,
 			keyID:        internalPluginSigner.keyID,
@@ -492,3 +492,53 @@ func basicSignTest(t *testing.T, ps *PluginSigner, envelopeType string, data []b
 	}
 	basicVerification(t, data, envelopeType, mockPlugin.certs[len(mockPlugin.certs)-1], &validMetadata)
 }
+
+func TestNewPluginPrimitiveSigner(t *testing.T) {
+	ctx := context.Background()
+	mp := newMockPlugin(defaultKeyCert.key, defaultKeyCert.certs, defaultKeySpec)
+
+	s := NewPluginPrimitiveSigner(ctx, mp, "testKeyID", defaultKeySpec, nil)
+
+	// verify KeySpec
+	ks, err := s.KeySpec()
+	if err != nil {
+		t.Fatalf("KeySpec() error: %v", err)
+	}
+	if ks != defaultKeySpec {
+		t.Fatalf("KeySpec() = %v, want %v", ks, defaultKeySpec)
+	}
+
+	// verify Sign
+	sig, certs, err := s.Sign([]byte("payload"))
+	if err != nil {
+		t.Fatalf("Sign() error: %v", err)
+	}
+	if len(sig) == 0 {
+		t.Fatal("Sign() returned empty signature")
+	}
+	if len(certs) == 0 {
+		t.Fatal("Sign() returned no certificates")
+	}
+}
+
+func TestGetKeySpecFromPlugin(t *testing.T) {
+	ctx := context.Background()
+	mp := newMockPlugin(defaultKeyCert.key, defaultKeyCert.certs, defaultKeySpec)
+
+	got, err := GetKeySpecFromPlugin(ctx, mp, "testKeyID", nil)
+	if err != nil {
+		t.Fatalf("GetKeySpecFromPlugin() error: %v", err)
+	}
+	if got != defaultKeySpec {
+		t.Fatalf("GetKeySpecFromPlugin() = %v, want %v", got, defaultKeySpec)
+	}
+}
+
+func TestGetKeySpecFromPlugin_Error(t *testing.T) {
+	ctx := context.Background()
+	mp := &mockPlugin{}
+	_, err := GetKeySpecFromPlugin(ctx, mp, "testKeyID", nil)
+	if err == nil {
+		t.Fatal("expected error for empty keySpec, got nil")
+	}
+}