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attest.go
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attest.go
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package secant
import (
"bytes"
"context"
"encoding/base64"
"encoding/json"
"fmt"
"io"
"log"
"net/url"
"os"
"github.com/google/go-containerregistry/pkg/name"
v1 "github.com/google/go-containerregistry/pkg/v1"
"github.com/google/go-containerregistry/pkg/v1/remote"
"github.com/jonjohnsonjr/secant/models/intoto"
"github.com/jonjohnsonjr/secant/tlog"
"github.com/jonjohnsonjr/secant/types"
"github.com/secure-systems-lab/go-securesystemslib/dsse"
"github.com/sigstore/cosign/v2/pkg/cosign/attestation"
cbundle "github.com/sigstore/cosign/v2/pkg/cosign/bundle"
cremote "github.com/sigstore/cosign/v2/pkg/cosign/remote"
"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"
ctypes "github.com/sigstore/cosign/v2/pkg/types"
"github.com/sigstore/rekor/pkg/generated/client"
"github.com/sigstore/sigstore/pkg/cryptoutils"
"github.com/sigstore/sigstore/pkg/signature/options"
)
// NewStatement generates a statement for use in Attest.
func NewStatement(digest name.Digest, predicate io.Reader, ptype string) (*types.Statement, error) {
h, err := v1.NewHash(digest.Identifier())
if err != nil {
return nil, err
}
sh, err := attestation.GenerateStatement(attestation.GenerateOpts{
Predicate: predicate,
Type: ptype,
Digest: h.Hex,
Repo: digest.Repository.String(),
})
if err != nil {
return nil, err
}
payload, err := json.Marshal(sh)
if err != nil {
return nil, fmt.Errorf("marshaling statement: %w", err)
}
return &types.Statement{
Digest: digest,
Type: ptype,
Payload: payload,
}, nil
}
// Attest is roughly equivalent to cosign attest.
// The only real implementation of types.CosignerSignerVerifier is fulcio.SignerVerifier.
func Attest(ctx context.Context, statement *types.Statement, sv types.CosignerSignerVerifier, rekorClient *client.Rekor, ropt []remote.Option) error {
pae := dsse.PAE(ctypes.IntotoPayloadType, statement.Payload)
signed, err := sv.SignMessage(bytes.NewReader(pae), options.WithContext(ctx))
if err != nil {
return fmt.Errorf("signing pae: %w", err)
}
env := dsse.Envelope{
PayloadType: ctypes.IntotoPayloadType,
Payload: base64.StdEncoding.EncodeToString(statement.Payload),
Signatures: []dsse.Signature{
{
Sig: base64.StdEncoding.EncodeToString(signed),
},
},
}
envelope, err := json.Marshal(env)
if err != nil {
return fmt.Errorf("marshaling envelope: %w", err)
}
// Use the inner Cosigner to safely generate a valid sig, then graft its values on our attestation.
sig, err := sv.Cosign(ctx, bytes.NewReader(envelope))
if err != nil {
return fmt.Errorf("signing envelope: %w", err)
}
cert, err := sig.Cert()
if err != nil {
return err
}
rawCert, err := cryptoutils.MarshalCertificateToPEM(cert)
if err != nil {
return err
}
chain, err := sig.Chain()
if err != nil {
return err
}
rawChain, err := cryptoutils.MarshalCertificatesToPEM(chain)
if err != nil {
return fmt.Errorf("marshaling chain: %w", err)
}
e, err := intoto.Entry(ctx, envelope, rawCert)
if err != nil {
return fmt.Errorf("creating intoto entry: %w", err)
}
log.Printf("debug envelope:\n%s", string(envelope))
log.Printf("debug rawCert:\n%s", string(rawCert))
entry, err := tlog.Upload(ctx, rekorClient, e)
if err != nil {
return fmt.Errorf("uploading to rekor: %w", err)
}
fmt.Fprintln(os.Stderr, "tlog entry created with index:", *entry.LogIndex)
bundle := cbundle.EntryToBundle(entry)
predicateType, err := parsePredicateType(statement.Type)
if err != nil {
return err
}
opts := []static.Option{
static.WithCertChain(rawCert, rawChain),
static.WithBundle(bundle),
static.WithLayerMediaType(ctypes.DssePayloadType),
static.WithAnnotations(map[string]string{
"predicateType": predicateType,
}),
}
att, err := static.NewAttestation(envelope, opts...)
if err != nil {
return err
}
// We don't actually need to access the remote entity to attach things to it
// so we use a placeholder here.
se := ociremote.SignedUnknown(statement.Digest)
signOpts := []mutate.SignOption{
mutate.WithDupeDetector(cremote.NewDupeDetector(sv)),
mutate.WithReplaceOp(cremote.NewReplaceOp(predicateType)),
}
// Attach the attestation to the entity.
se, err = mutate.AttachAttestationToEntity(se, att, signOpts...)
if err != nil {
return err
}
// Publish the attestations associated with this entity
ropts := []ociremote.Option{ociremote.WithRemoteOptions(ropt...)}
return ociremote.WriteAttestations(statement.Digest.Repository, se, ropts...)
}
var predicateTypeMap = map[string]string{
"custom": "https://cosign.sigstore.dev/attestation/v1",
"slsaprovenance": "https://slsa.dev/provenance/v0.2",
"spdx": "https://spdx.dev/Document",
"spdxjson": "https://spdx.dev/Document",
"cyclonedx": "https://cyclonedx.org/bom",
"link": "https://in-toto.io/Link/v1",
"vuln": "https://cosign.sigstore.dev/attestation/vuln/v1",
}
func parsePredicateType(t string) (string, error) {
uri, ok := predicateTypeMap[t]
if !ok {
if _, err := url.ParseRequestURI(t); err != nil {
return "", fmt.Errorf("invalid predicate type: %s", t)
}
uri = t
}
return uri, nil
}