Honor creation timestamp for signatures again

cmd/cosign/cli/options/sign.go

@@ -21,26 +21,27 @@ import (
 
 // SignOptions is the top level wrapper for the sign command.
 type SignOptions struct {
-	Key                   string
-	Cert                  string
-	CertChain             string
-	Upload                bool
-	Output                string // deprecated: TODO remove when the output flag is fully deprecated
-	OutputSignature       string // TODO: this should be the root output file arg.
-	OutputPayload         string
-	OutputCertificate     string
-	PayloadPath           string
-	Recursive             bool
-	Attachment            string
-	SkipConfirmation      bool
-	TlogUpload            bool
-	TSAClientCACert       string
-	TSAClientCert         string
-	TSAClientKey          string
-	TSAServerName         string
-	TSAServerURL          string
-	IssueCertificate      bool
-	SignContainerIdentity string
+	Key                     string
+	Cert                    string
+	CertChain               string
+	Upload                  bool
+	Output                  string // deprecated: TODO remove when the output flag is fully deprecated
+	OutputSignature         string // TODO: this should be the root output file arg.
+	OutputPayload           string
+	OutputCertificate       string
+	PayloadPath             string
+	Recursive               bool
+	Attachment              string
+	SkipConfirmation        bool
+	TlogUpload              bool
+	TSAClientCACert         string
+	TSAClientCert           string
+	TSAClientKey            string
+	TSAServerName           string
+	TSAServerURL            string
+	IssueCertificate        bool
+	SignContainerIdentity   string
+	RecordCreationTimestamp bool
 
 	Rekor       RekorOptions
 	Fulcio      FulcioOptions
@@ -130,4 +131,6 @@ func (o *SignOptions) AddFlags(cmd *cobra.Command) {
 
 	cmd.Flags().StringVar(&o.SignContainerIdentity, "sign-container-identity", "",
 		"manually set the .critical.docker-reference field for the signed identity, which is useful when image proxies are being used where the pull reference should match the signature")
+
+	cmd.Flags().BoolVar(&o.RecordCreationTimestamp, "record-creation-timestamp", false, "set the createdAt timestamp in the signature artifact to the time it was created; by default, cosign sets this to the zero value")
 }

cmd/cosign/cli/sign.go

@@ -83,7 +83,10 @@ race conditions or (worse) malicious tampering.
   cosign sign --key cosign.key --tlog-upload=false <IMAGE DIGEST>
 
   # sign a container image by manually setting the container image identity
-  cosign sign --sign-container-identity <NEW IMAGE DIGEST> <IMAGE DIGEST>`,
+  cosign sign --sign-container-identity <NEW IMAGE DIGEST> <IMAGE DIGEST>
+
+  # sign a container image and honor the creation timestamp of the signature
+  cosign sign --key cosign.key --record-creation-timestamp <IMAGE DIGEST>`,
 
 		Args:             cobra.MinimumNArgs(1),
 		PersistentPreRun: options.BindViper,

cmd/cosign/cli/sign/sign.go

@@ -329,7 +329,7 @@ func signDigest(ctx context.Context, digest name.Digest, payload []byte, ko opti
 	}
 
 	// Attach the signature to the entity.
-	newSE, err := mutate.AttachSignatureToEntity(se, ociSig, mutate.WithDupeDetector(dd))
+	newSE, err := mutate.AttachSignatureToEntity(se, ociSig, mutate.WithDupeDetector(dd), mutate.WithRecordCreationTimestamp(signOpts.RecordCreationTimestamp))
 	if err != nil {
 		return err
 	}

pkg/oci/mutate/mutate.go

@@ -377,5 +377,5 @@ func (so *signOpts) dedupeAndReplace(sig oci.Signature, basefn func() (oci.Signa
 		}
 		return ReplaceSignatures(replace)
 	}
-	return AppendSignatures(base, sig)
+	return AppendSignatures(base, so.rct, sig)
 }

pkg/oci/mutate/options.go

@@ -33,8 +33,9 @@ type ReplaceOp interface {
 type SignOption func(*signOpts)
 
 type signOpts struct {
-	dd DupeDetector
-	ro ReplaceOp
+	dd  DupeDetector
+	ro  ReplaceOp
+	rct bool
 }
 
 func makeSignOpts(opts ...SignOption) *signOpts {
@@ -59,6 +60,12 @@ func WithReplaceOp(ro ReplaceOp) SignOption {
 	}
 }
 
+func WithRecordCreationTimestamp(rct bool) SignOption {
+	return func(so *signOpts) {
+		so.rct = rct
+	}
+}
+
 type signatureOpts struct {
 	annotations      map[string]string
 	bundle           *bundle.RekorBundle

pkg/oci/mutate/signatures.go

@@ -19,12 +19,13 @@ import (
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
+	"github.com/sigstore/cosign/v2/internal/pkg/now"
 	"github.com/sigstore/cosign/v2/pkg/oci"
 )
 
 // AppendSignatures produces a new oci.Signatures with the provided signatures
 // appended to the provided base signatures.
-func AppendSignatures(base oci.Signatures, sigs ...oci.Signature) (oci.Signatures, error) {
+func AppendSignatures(base oci.Signatures, recordCreationTimestamp bool, sigs ...oci.Signature) (oci.Signatures, error) {
 	adds := make([]mutate.Addendum, 0, len(sigs))
 	for _, sig := range sigs {
 		ann, err := sig.Annotations()
@@ -42,6 +43,19 @@ func AppendSignatures(base oci.Signatures, sigs ...oci.Signature) (oci.Signature
 		return nil, err
 	}
 
+	if recordCreationTimestamp {
+		t, err := now.Now()
+		if err != nil {
+			return nil, err
+		}
+
+		// Set the Created date to time of execution
+		img, err = mutate.CreatedAt(img, v1.Time{Time: t})
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	return &sigAppender{
 		Image: img,
 		base:  base,

pkg/oci/mutate/signatures_test.go

@@ -38,17 +38,17 @@ func TestAppendSignatures(t *testing.T) {
 		t.Fatalf("NewSignature() = %v", err)
 	}
 
-	oneSig, err := AppendSignatures(base, s1)
+	oneSig, err := AppendSignatures(base, false, s1)
 	if err != nil {
 		t.Fatalf("AppendSignatures() = %v", err)
 	}
 
-	twoSig, err := AppendSignatures(oneSig, s2)
+	twoSig, err := AppendSignatures(oneSig, false, s2)
 	if err != nil {
 		t.Fatalf("AppendSignatures() = %v", err)
 	}
 
-	threeSig, err := AppendSignatures(oneSig, s2, s3)
+	threeSig, err := AppendSignatures(oneSig, true, s2, s3)
 	if err != nil {
 		t.Fatalf("AppendSignatures() = %v", err)
 	}
@@ -73,7 +73,13 @@ func TestAppendSignatures(t *testing.T) {
 
 	if testCfg, err := threeSig.ConfigFile(); err != nil {
 		t.Fatalf("ConfigFile() = %v", err)
-	} else if !testCfg.Created.Time.IsZero() {
-		t.Errorf("Date of Signature was not Zero")
+	} else if testCfg.Created.Time.IsZero() {
+		t.Errorf("Date of Signature was Zero")
+	}
+
+	if testDefaultCfg, err := twoSig.ConfigFile(); err != nil {
+		t.Fatalf("ConfigFile() = %v", err)
+	} else if !testDefaultCfg.Created.Time.IsZero() {
+		t.Errorf("Date of Signature was Zero")
 	}
 }

pkg/oci/static/file.go

@@ -22,6 +22,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/types"
+	"github.com/sigstore/cosign/v2/internal/pkg/now"
 	"github.com/sigstore/cosign/v2/pkg/oci"
 	"github.com/sigstore/cosign/v2/pkg/oci/signed"
 )
@@ -48,6 +49,19 @@ func NewFile(payload []byte, opts ...Option) (oci.File, error) {
 	// Add annotations from options
 	img = mutate.Annotations(img, o.Annotations).(v1.Image)
 
+	if o.RecordCreationTimestamp {
+		t, err := now.Now()
+		if err != nil {
+			return nil, err
+		}
+
+		// Set the Created date to time of execution
+		img, err = mutate.CreatedAt(img, v1.Time{Time: t})
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	return &file{
 		SignedImage: signed.Image(img),
 		layer:       layer,

pkg/oci/static/file_test.go

@@ -32,6 +32,12 @@ func TestNewFile(t *testing.T) {
 		t.Fatalf("NewFile() = %v", err)
 	}
 
+	timestampedFile, err := NewFile([]byte(payload), WithLayerMediaType("foo"), WithAnnotations(map[string]string{"foo": "bar"}), WithRecordCreationTimestamp(true))
+
+	if err != nil {
+		t.Fatalf("NewFile() = %v", err)
+	}
+
 	layers, err := file.Layers()
 	if err != nil {
 		t.Fatalf("Layers() = %v", err)
@@ -129,6 +135,13 @@ func TestNewFile(t *testing.T) {
 		if !fileCfg.Created.Time.IsZero() {
 			t.Errorf("Date of Signature was not Zero")
 		}
+		tsCfg, err := timestampedFile.ConfigFile()
+		if err != nil {
+			t.Fatalf("ConfigFile() = %v", err)
+		}
+		if tsCfg.Created.Time.IsZero() {
+			t.Errorf("Date of Signature was Zero")
+		}
 	})
 
 	t.Run("check annotations", func(t *testing.T) {

pkg/oci/static/options.go

@@ -27,13 +27,14 @@ import (
 type Option func(*options)
 
 type options struct {
-	LayerMediaType   types.MediaType
-	ConfigMediaType  types.MediaType
-	Bundle           *bundle.RekorBundle
-	RFC3161Timestamp *bundle.RFC3161Timestamp
-	Cert             []byte
-	Chain            []byte
-	Annotations      map[string]string
+	LayerMediaType          types.MediaType
+	ConfigMediaType         types.MediaType
+	Bundle                  *bundle.RekorBundle
+	RFC3161Timestamp        *bundle.RFC3161Timestamp
+	Cert                    []byte
+	Chain                   []byte
+	Annotations             map[string]string
+	RecordCreationTimestamp bool
 }
 
 func makeOptions(opts ...Option) (*options, error) {
@@ -112,3 +113,10 @@ func WithCertChain(cert, chain []byte) Option {
 		o.Chain = chain
 	}
 }
+
+// WithRecordCreationTimestamp sets the feature flag to honor the creation timestamp to time of running
+func WithRecordCreationTimestamp(rct bool) Option {
+	return func(o *options) {
+		o.RecordCreationTimestamp = rct
+	}
+}