Merge pull request #147 from puerco/att-verify

Fix keyless verification of openvex attesatations

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/owenrumney/go-sarif v1.1.1
 	github.com/secure-systems-lab/go-securesystemslib v0.7.0
 	github.com/sigstore/cosign/v2 v2.2.2
+	github.com/sigstore/rekor v1.3.4
 	github.com/sigstore/sigstore v1.7.6
 	github.com/sirupsen/logrus v1.9.3
 	github.com/spf13/cobra v1.8.0
@@ -145,7 +146,6 @@ require (
 	github.com/sassoftware/relic v7.2.1+incompatible // indirect
 	github.com/segmentio/ksuid v1.0.4 // indirect
 	github.com/sigstore/fulcio v1.4.3 // indirect
-	github.com/sigstore/rekor v1.3.4 // indirect
 	github.com/sigstore/timestamp-authority v1.2.0 // indirect
 	github.com/skratchdot/open-golang v0.0.0-20200116055534-eef842397966 // indirect
 	github.com/sourcegraph/conc v0.3.0 // indirect

pkg/attestation/attestation.go

@@ -11,22 +11,45 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"os"
 	"strings"
-	"time"
 
 	"github.com/google/go-containerregistry/pkg/crane"
 	intoto "github.com/in-toto/in-toto-golang/in_toto"
 	ovattest "github.com/openvex/go-vex/pkg/attestation"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
+	"github.com/sigstore/cosign/v2/cmd/cosign/cli/rekor"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/sign"
+	"github.com/sigstore/cosign/v2/pkg/cosign"
+	"github.com/sigstore/rekor/pkg/generated/models"
 	"github.com/sigstore/sigstore/pkg/signature/dsse"
 	signatureoptions "github.com/sigstore/sigstore/pkg/signature/options"
 )
 
 type Attestation struct {
-	signedData []byte `json:"-"`
 	ovattest.Attestation
+
+	// Sign is boolean that signals if the attestation has been signed
 	Signed bool `json:"-"`
+
+	// signatureData embeds the signed attestaion, the certificate used to sign
+	// it and the transparency log inclusion proof
+	SignatureData *SignatureData `json:"-"`
+}
+
+type SignatureData struct {
+	// CertData of the cert used to sign the attestation encodeded in PEM
+	CertData []byte `json:"-"`
+
+	// Chain contains the intermediate certificate chain of the attestation's cert
+	Chain []byte `json:"-"`
+
+	// Entry contains the proof of inclusion to the transparency log
+	Entry *models.LogEntryAnon `json:"-"`
+
+	// signedPayload contains the resulting blob after the attestation was
+	// signed.
+	signedPayload []byte
 }
 
 func New() *Attestation {
@@ -38,51 +61,18 @@ func New() *Attestation {
 
 // Sign the attestation
 func (att *Attestation) Sign() error {
-	ctx := context.Background()
-	var timeout time.Duration /// TODO move to options
-	var certPath, certChainPath string
-	ko := options.KeyOpts{
-		// KeyRef:     s.options.PrivateKeyPath,
-		// IDToken:    identityToken,
-		FulcioURL:    options.DefaultFulcioURL,
-		RekorURL:     options.DefaultRekorURL,
-		OIDCIssuer:   options.DefaultOIDCIssuerURL,
-		OIDCClientID: "sigstore",
-
-		InsecureSkipFulcioVerify: false,
-		SkipConfirmation:         true,
-		// FulcioAuthFlow:           "",
-	}
-
-	if timeout != 0 {
-		var cancelFn context.CancelFunc
-		ctx, cancelFn = context.WithTimeout(ctx, timeout)
-		defer cancelFn()
-	}
-
-	sv, err := sign.SignerFromKeyOpts(ctx, certPath, certChainPath, ko)
-	if err != nil {
-		return fmt.Errorf("getting signer: %w", err)
-	}
-	defer sv.Close()
+	ctx, ko := initSigning()
 
-	// Wrap the attestation in the DSSE envelope
-	wrapped := dsse.WrapSigner(sv, "application/vnd.in-toto+json")
-
-	var b bytes.Buffer
-	if err := att.ToJSON(&b); err != nil {
-		return fmt.Errorf("serializing attestation to json: %w", err)
+	// Sign the attestaion.
+	if err := signAttestation(ctx, &ko, att); err != nil {
+		return fmt.Errorf("signing attestation: %w", err)
 	}
 
-	signedPayload, err := wrapped.SignMessage(
-		bytes.NewReader(b.Bytes()), signatureoptions.WithContext(ctx),
-	)
-	if err != nil {
-		return fmt.Errorf("signing attestation: %w", err)
+	// Register the signature in rekor
+	if err := appendSignatureDataToTLog(ctx, &ko, att); err != nil {
+		return fmt.Errorf("recording signature data to transparency log: %w", err)
 	}
 
-	att.Signed = true
-	att.signedData = signedPayload
 	return nil
 }
 
@@ -114,12 +104,100 @@ func (att *Attestation) ToJSON(w io.Writer) error {
 	if !att.Signed {
 		return att.Attestation.ToJSON(w)
 	}
-	if len(att.signedData) == 0 {
+	if att.SignatureData == nil || len(att.SignatureData.signedPayload) == 0 {
 		return errors.New("consistency error: attestation is signed but data is empty")
 	}
 
-	if _, err := w.Write(att.signedData); err != nil {
+	if _, err := w.Write(att.SignatureData.signedPayload); err != nil {
 		return fmt.Errorf("writing signed attestation: %w", err)
 	}
 	return nil
 }
+
+// initSigning initializes the options and context needed to sign. Right now
+// it only sets up some default options and a backgrous context but we
+// should wire the options set from the CLI to this function
+func initSigning() (context.Context, options.KeyOpts) {
+	ko := options.KeyOpts{
+		FulcioURL:                options.DefaultFulcioURL,
+		RekorURL:                 options.DefaultRekorURL,
+		OIDCIssuer:               options.DefaultOIDCIssuerURL,
+		OIDCClientID:             "sigstore",
+		InsecureSkipFulcioVerify: false,
+		SkipConfirmation:         true,
+	}
+
+	ctx := context.Background()
+	// TODO(puerco): Support context.WithTimeout(ctx, timeout)
+
+	return ctx, ko
+}
+
+// signAttestation creates a signer and signs the attestation. The attestation's
+// SignatureData field will be populated with the certificate, chain and the
+// attestaion data wrapped in its DSSE envelope.
+func signAttestation(ctx context.Context, ko *options.KeyOpts, att *Attestation) error {
+	// TODO(puerco): Investigate supporting certificates preloaded in the
+	// attestation. We would need to dump them to disk and load them into
+	// the args here and if we're reusing the bundle, set it in ko.BundlePath
+	// Note that in this call we hardocde the pats empty, but we should get them
+	// from somewhere.
+	sv, err := sign.SignerFromKeyOpts(ctx, "", "", *ko)
+	if err != nil {
+		return fmt.Errorf("getting signer: %w", err)
+	}
+	defer sv.Close()
+
+	// Wrap the attestation in the DSSE envelope
+	wrapped := dsse.WrapSigner(sv, "application/vnd.in-toto+json")
+
+	var b bytes.Buffer
+	if err := att.ToJSON(&b); err != nil {
+		return fmt.Errorf("serializing attestation to json: %w", err)
+	}
+
+	// SIGN!
+	signedPayload, err := wrapped.SignMessage(
+		bytes.NewReader(b.Bytes()), signatureoptions.WithContext(ctx),
+	)
+	if err != nil {
+		return fmt.Errorf("signing attestation: %w", err)
+	}
+
+	// Assign the new data to the attestation
+	att.SignatureData = &SignatureData{
+		CertData:      sv.Cert,
+		Chain:         sv.Chain,
+		signedPayload: signedPayload,
+	}
+	att.Signed = true
+
+	return nil
+}
+
+// appendSignatureDataToTLog records the signature data to the transparency log
+// (rekor). The proof of inclusion will be added to the attestation's SignatureData
+// struct.
+// If uploading fails, the signature data will be destroyed to guarantee an atomic
+// operation of attesation.Sign()
+func appendSignatureDataToTLog(ctx context.Context, ko *options.KeyOpts, att *Attestation) error {
+	tlogClient, err := rekor.NewClient(ko.RekorURL)
+	if err != nil {
+		att.SignatureData = nil
+		return fmt.Errorf("creating rekor client: %w", err)
+	}
+
+	// ...and upload the signature data
+	entry, err := cosign.TLogUploadDSSEEnvelope(
+		ctx, tlogClient, att.SignatureData.signedPayload, att.SignatureData.CertData,
+	)
+	if err != nil {
+		att.SignatureData = nil
+		return fmt.Errorf("uploading to transparency log: %w", err)
+	}
+
+	att.SignatureData.Entry = entry
+	fmt.Fprintln(os.Stderr, "tlog entry created with index:", *entry.LogIndex)
+
+	return nil
+}

pkg/ctl/implementation.go

@@ -23,6 +23,7 @@ import (
 	ssldsse "github.com/secure-systems-lab/go-securesystemslib/dsse"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/v2/pkg/cosign"
+	cbundle "github.com/sigstore/cosign/v2/pkg/cosign/bundle"
 	"github.com/sigstore/cosign/v2/pkg/oci/mutate"
 	ociremote "github.com/sigstore/cosign/v2/pkg/oci/remote"
 	"github.com/sigstore/cosign/v2/pkg/oci/static"
@@ -185,7 +186,7 @@ func (impl *defaultVexCtlImplementation) Attach(ctx context.Context, att *attest
 		}
 
 		for _, ref := range refs {
-			if err := attachAttestation(ctx, payload, ref); err != nil {
+			if err := attachAttestation(ctx, att, payload, ref); err != nil {
 				return fmt.Errorf("attaching attestation to %s: %w", ref, err)
 			}
 		}
@@ -196,7 +197,7 @@ func (impl *defaultVexCtlImplementation) Attach(ctx context.Context, att *attest
 
 // attachAttestation is a utility function to do the actual attachment of
 // the signed attestation
-func attachAttestation(ctx context.Context, payload []byte, imageRef string) error {
+func attachAttestation(ctx context.Context, original *attestation.Attestation, payload []byte, imageRef string) error {
 	regOpts := options.RegistryOptions{}
 	remoteOpts, err := regOpts.ClientOpts(ctx)
 	if err != nil {
@@ -216,6 +217,22 @@ func attachAttestation(ctx context.Context, payload []byte, imageRef string) err
 	ref = digest //nolint:ineffassign
 
 	opts := []static.Option{static.WithLayerMediaType(types.DssePayloadType)}
+
+	// Add the attestation certificate:
+	opts = append(opts, static.WithCertChain(original.SignatureData.CertData, original.SignatureData.Chain))
+
+	// Add the tlog entry to the annotations
+	if original.SignatureData.Entry != nil {
+		opts = append(opts, static.WithBundle(
+			cbundle.EntryToBundle(original.SignatureData.Entry),
+		))
+	}
+
+	// Add predicateType as manifest annotation
+	opts = append(opts, static.WithAnnotations(map[string]string{
+		"predicateType": vex.Context,
+	}))
+
 	att, err := static.NewAttestation(payload, opts...)
 	if err != nil {
 		return err