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Verify SCTs returned by fulcio (#600)
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Added in the CT log public key for this verification.

Signed-off-by: Priya Wadhwa <priyawadhwa@google.com>
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priyawadhwa authored Sep 1, 2021
1 parent c79ba73 commit cb9f980
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Showing 4 changed files with 223 additions and 32 deletions.
86 changes: 74 additions & 12 deletions cmd/cosign/cli/fulcio/fulcio.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,8 @@ import (
"crypto/sha256"
"crypto/x509"
_ "embed" // To enable the `go:embed` directive.
"encoding/base64"
"encoding/json"
"encoding/pem"
"fmt"
"io/ioutil"
Expand All @@ -34,6 +36,10 @@ import (
"github.com/go-openapi/runtime"
httptransport "github.com/go-openapi/runtime/client"
"github.com/go-openapi/strfmt"
ct "github.com/google/certificate-transparency-go"
"github.com/google/certificate-transparency-go/ctutil"
ctx509 "github.com/google/certificate-transparency-go/x509"
"github.com/google/certificate-transparency-go/x509util"
"github.com/pkg/errors"
"golang.org/x/term"

Expand All @@ -53,11 +59,24 @@ const (
altRoot = "SIGSTORE_ROOT_FILE"
)

type Resp struct {
CertPEM []byte
ChainPEM []byte
SCT []byte
}

// This is the root in the fulcio project.
//go:embed fulcio.pem
var rootPem string

var ctPublicKeyStr = `ctfe.pub`
var fulcioTargetStr = `fulcio.crt.pem`

var (
// For testing
VerifySCT = verifySCT
)

type oidcConnector interface {
OIDConnect(string, string, string) (*oauthflow.OIDCIDToken, error)
}
Expand All @@ -74,22 +93,22 @@ type signingCertProvider interface {
SigningCert(params *operations.SigningCertParams, authInfo runtime.ClientAuthInfoWriter, opts ...operations.ClientOption) (*operations.SigningCertCreated, error)
}

func getCertForOauthID(priv *ecdsa.PrivateKey, scp signingCertProvider, connector oidcConnector, oidcIssuer string, oidcClientID string) (certPem, chainPem []byte, err error) {
func getCertForOauthID(priv *ecdsa.PrivateKey, scp signingCertProvider, connector oidcConnector, oidcIssuer string, oidcClientID string) (Resp, error) {
pubBytes, err := x509.MarshalPKIXPublicKey(&priv.PublicKey)
if err != nil {
return nil, nil, err
return Resp{}, err
}

tok, err := connector.OIDConnect(oidcIssuer, oidcClientID, "")
if err != nil {
return nil, nil, err
return Resp{}, err
}

// Sign the email address as part of the request
h := sha256.Sum256([]byte(tok.Subject))
proof, err := ecdsa.SignASN1(rand.Reader, priv, h[:])
if err != nil {
return nil, nil, err
return Resp{}, err
}

bearerAuth := httptransport.BearerToken(tok.RawString)
Expand All @@ -109,17 +128,58 @@ func getCertForOauthID(priv *ecdsa.PrivateKey, scp signingCertProvider, connecto

resp, err := scp.SigningCert(params, bearerAuth)
if err != nil {
return nil, nil, err
return Resp{}, err
}
sct, err := base64.StdEncoding.DecodeString(resp.SCT.String())
if err != nil {
return Resp{}, err
}

// split the cert and the chain
certBlock, chainPem := pem.Decode([]byte(resp.Payload))
certPem = pem.EncodeToMemory(certBlock)
return certPem, chainPem, nil
certPem := pem.EncodeToMemory(certBlock)
fr := Resp{
CertPEM: certPem,
ChainPEM: chainPem,
SCT: sct,
}

// verify the sct
if err := VerifySCT(fr); err != nil {
fmt.Printf("Unable to verify SCT: %v\n", err)
} else {
fmt.Println("Successfully verified SCT...")
}
return fr, nil
}

// verifySCT verifies the SCT against the Fulcio CT log public key
// The SCT is a `Signed Certificate Timestamp`, which promises that
// the certificate issued by Fulcio was also added to the public CT log within
// some defined time period
func verifySCT(fr Resp) error {
buf := tuf.ByteDestination{Buffer: &bytes.Buffer{}}
if err := tuf.GetTarget(context.TODO(), ctPublicKeyStr, &buf); err != nil {
fmt.Println("Unable to verify SCT, try running `cosign init`...")
return err
}
pubKey, err := cosign.PemToECDSAKey(buf.Bytes())
if err != nil {
return err
}
cert, err := x509util.CertificateFromPEM(fr.CertPEM)
if err != nil {
return err
}
var sct ct.SignedCertificateTimestamp
if err := json.Unmarshal(fr.SCT, &sct); err != nil {
return errors.Wrap(err, "unmarshal")
}
return ctutil.VerifySCT(pubKey, []*ctx509.Certificate{cert}, &sct, false)
}

// GetCert returns the PEM-encoded signature of the OIDC identity returned as part of an interactive oauth2 flow plus the PEM-encoded cert chain.
func GetCert(ctx context.Context, priv *ecdsa.PrivateKey, idToken, flow, oidcIssuer, oidcClientID string, fClient *fulcioClient.Fulcio) (certPemBytes, chainPemBytes []byte, err error) {
func GetCert(ctx context.Context, priv *ecdsa.PrivateKey, idToken, flow, oidcIssuer, oidcClientID string, fClient *fulcioClient.Fulcio) (Resp, error) {
c := &realConnector{}
switch flow {
case FlowDevice:
Expand All @@ -130,7 +190,7 @@ func GetCert(ctx context.Context, priv *ecdsa.PrivateKey, idToken, flow, oidcIss
case FlowToken:
c.flow = &oauthflow.StaticTokenGetter{RawToken: idToken}
default:
return nil, nil, fmt.Errorf("unsupported oauth flow: %s", flow)
return Resp{}, fmt.Errorf("unsupported oauth flow: %s", flow)
}

return getCertForOauthID(priv, fClient.Operations, c, oidcIssuer, oidcClientID)
Expand All @@ -139,6 +199,7 @@ func GetCert(ctx context.Context, priv *ecdsa.PrivateKey, idToken, flow, oidcIss
type Signer struct {
Cert []byte
Chain []byte
SCT []byte
pub *ecdsa.PublicKey
*signature.ECDSASignerVerifier
}
Expand All @@ -164,15 +225,16 @@ func NewSigner(ctx context.Context, idToken, oidcIssuer, oidcClientID string, fC
default:
flow = FlowNormal
}
cert, chain, err := GetCert(ctx, priv, idToken, flow, oidcIssuer, oidcClientID, fClient) // TODO, use the chain.
Resp, err := GetCert(ctx, priv, idToken, flow, oidcIssuer, oidcClientID, fClient) // TODO, use the chain.
if err != nil {
return nil, errors.Wrap(err, "retrieving cert")
}
f := &Signer{
pub: &priv.PublicKey,
ECDSASignerVerifier: signer,
Cert: cert,
Chain: chain,
Cert: Resp.CertPEM,
Chain: Resp.ChainPEM,
SCT: Resp.SCT,
}
return f, nil

Expand Down
11 changes: 7 additions & 4 deletions cmd/cosign/cli/fulcio/fulcio_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,10 @@ func TestGetCertForOauthID(t *testing.T) {
err: tc.tokenGetterErr,
}

cert, chain, err := getCertForOauthID(testKey, tscp, &tf, "", "")
VerifySCT = func(Resp) error { return nil }
defer func() { VerifySCT = verifySCT }()

resp, err := getCertForOauthID(testKey, tscp, &tf, "", "")

if err != nil {
if !tc.expectErr {
Expand All @@ -122,16 +125,16 @@ func TestGetCertForOauthID(t *testing.T) {
return
}
if tc.expectErr {
t.Fatalf("getCertForOauthID got: %q, %q wanted error", cert, chain)
t.Fatalf("getCertForOauthID got: %q, %q wanted error", resp.CertPEM, resp.ChainPEM)
}

expectedCert := string(expectedCertBytes)
actualCert := string(cert)
actualCert := string(resp.CertPEM)
if actualCert != expectedCert {
t.Errorf("getCertForOauthID returned cert %q, wanted %q", actualCert, expectedCert)
}
expectedChain := string(expectedExtraBytes)
actualChain := string(chain)
actualChain := string(resp.ChainPEM)
if actualChain != expectedChain {
t.Errorf("getCertForOauthID returned chain %q, wanted %q", actualChain, expectedChain)
}
Expand Down
76 changes: 67 additions & 9 deletions go.mod
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ module github.com/sigstore/cosign
go 1.17

require (
cloud.google.com/go v0.90.0 // indirect
cloud.google.com/go v0.92.3 // indirect
cloud.google.com/go/storage v1.16.0
github.com/Azure/azure-sdk-for-go v55.8.0+incompatible // indirect
github.com/Azure/go-autorest v14.2.0+incompatible // indirect
Expand Down Expand Up @@ -45,7 +45,7 @@ require (
github.com/go-logr/logr v0.4.0 // indirect
github.com/go-logr/zapr v0.4.0 // indirect
github.com/go-openapi/analysis v0.20.1 // indirect
github.com/go-openapi/errors v0.20.0 // indirect
github.com/go-openapi/errors v0.20.1 // indirect
github.com/go-openapi/jsonpointer v0.19.5 // indirect
github.com/go-openapi/jsonreference v0.19.6 // indirect
github.com/go-openapi/loads v0.20.2 // indirect
Expand Down Expand Up @@ -88,7 +88,6 @@ require (
github.com/jmespath/go-jmespath v0.4.0 // indirect
github.com/josharian/intern v1.0.0 // indirect
github.com/json-iterator/go v1.1.11 // indirect
github.com/jstemmer/go-junit-report v0.9.1 // indirect
github.com/juju/ansiterm v0.0.0-20180109212912-720a0952cc2a // indirect
github.com/klauspost/compress v1.13.0 // indirect
github.com/leodido/go-urn v1.2.1 // indirect
Expand Down Expand Up @@ -125,7 +124,7 @@ require (
github.com/sassoftware/relic v0.0.0-20210427151427-dfb082b79b74 // indirect
github.com/segmentio/ksuid v1.0.4 // indirect
github.com/shibumi/go-pathspec v1.2.0 // indirect
github.com/sigstore/fulcio v0.1.1
github.com/sigstore/fulcio v0.1.2-0.20210831152525-42f7422734bb
github.com/sigstore/rekor v0.3.0
github.com/sigstore/sigstore v0.0.0-20210729211320-56a91f560f44
github.com/sirupsen/logrus v1.8.1 // indirect
Expand All @@ -149,9 +148,8 @@ require (
go.uber.org/atomic v1.8.0 // indirect
go.uber.org/automaxprocs v1.4.0 // indirect
go.uber.org/multierr v1.7.0 // indirect
go.uber.org/zap v1.18.1 // indirect
go.uber.org/zap v1.19.0 // indirect
golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97 // indirect
golang.org/x/lint v0.0.0-20210508222113-6edffad5e616 // indirect
golang.org/x/mod v0.4.2 // indirect
golang.org/x/net v0.0.0-20210614182718-04defd469f4e // indirect
golang.org/x/oauth2 v0.0.0-20210805134026-6f1e6394065a // indirect
Expand All @@ -160,12 +158,10 @@ require (
golang.org/x/term v0.0.0-20210615171337-6886f2dfbf5b
golang.org/x/text v0.3.6 // indirect
golang.org/x/time v0.0.0-20210723032227-1f47c861a9ac // indirect
golang.org/x/tools v0.1.5 // indirect
golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
gomodules.xyz/jsonpatch/v2 v2.2.0 // indirect
google.golang.org/api v0.54.0
google.golang.org/appengine v1.6.7 // indirect
google.golang.org/genproto v0.0.0-20210805201207-89edb61ffb67 // indirect
google.golang.org/genproto v0.0.0-20210813162853-db860fec028c // indirect
google.golang.org/grpc v1.39.1 // indirect
google.golang.org/protobuf v1.27.1 // indirect
gopkg.in/inf.v0 v0.9.1 // indirect
Expand All @@ -185,3 +181,65 @@ require (
sigs.k8s.io/structured-merge-diff/v4 v4.1.2 // indirect
sigs.k8s.io/yaml v1.2.0 // indirect
)

require (
cloud.google.com/go/kms v0.1.0 // indirect
cloud.google.com/go/security v0.1.0 // indirect
github.com/ThalesIgnite/crypto11 v1.2.4 // indirect
github.com/bgentry/speakeasy v0.1.0 // indirect
github.com/census-instrumentation/opencensus-proto v0.3.0 // indirect
github.com/cncf/udpa/go v0.0.0-20201120205902-5459f2c99403 // indirect
github.com/cncf/xds/go v0.0.0-20210312221358-fbca930ec8ed // indirect
github.com/coreos/go-semver v0.3.0 // indirect
github.com/coreos/go-systemd/v22 v22.3.2 // indirect
github.com/cpuguy83/go-md2man/v2 v2.0.0 // indirect
github.com/docker/go-units v0.4.0 // indirect
github.com/dustin/go-humanize v1.0.0 // indirect
github.com/envoyproxy/go-control-plane v0.9.9-0.20210512163311-63b5d3c536b0 // indirect
github.com/envoyproxy/protoc-gen-validate v0.3.0-java // indirect
github.com/fullstorydev/grpcurl v1.8.1 // indirect
github.com/golang/glog v0.0.0-20210429001901-424d2337a529 // indirect
github.com/golang/mock v1.6.0 // indirect
github.com/google/btree v1.0.1 // indirect
github.com/google/certificate-transparency-go v1.1.2-0.20210512142713-bed466244fa6 // indirect
github.com/gorilla/websocket v1.4.2 // indirect
github.com/grpc-ecosystem/go-grpc-middleware v1.3.0 // indirect
github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 // indirect
github.com/grpc-ecosystem/grpc-gateway v1.16.0 // indirect
github.com/jhump/protoreflect v1.8.2 // indirect
github.com/jonboulle/clockwork v0.2.2 // indirect
github.com/miekg/pkcs11 v1.0.3 // indirect
github.com/rs/cors v1.8.0 // indirect
github.com/russross/blackfriday/v2 v2.1.0 // indirect
github.com/soheilhy/cmux v0.1.5 // indirect
github.com/thales-e-security/pool v0.0.2 // indirect
github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802 // indirect
github.com/urfave/cli v1.22.4 // indirect
github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect
go.etcd.io/bbolt v1.3.6 // indirect
go.etcd.io/etcd/api/v3 v3.5.0 // indirect
go.etcd.io/etcd/client/pkg/v3 v3.5.0 // indirect
go.etcd.io/etcd/client/v2 v2.305.0 // indirect
go.etcd.io/etcd/client/v3 v3.5.0 // indirect
go.etcd.io/etcd/etcdctl/v3 v3.5.0 // indirect
go.etcd.io/etcd/etcdutl/v3 v3.5.0 // indirect
go.etcd.io/etcd/pkg/v3 v3.5.0 // indirect
go.etcd.io/etcd/raft/v3 v3.5.0 // indirect
go.etcd.io/etcd/server/v3 v3.5.0 // indirect
go.etcd.io/etcd/tests/v3 v3.5.0 // indirect
go.etcd.io/etcd/v3 v3.5.0 // indirect
go.opentelemetry.io/contrib v0.20.0 // indirect
go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.20.0 // indirect
go.opentelemetry.io/otel v0.20.0 // indirect
go.opentelemetry.io/otel/exporters/otlp v0.20.0 // indirect
go.opentelemetry.io/otel/metric v0.20.0 // indirect
go.opentelemetry.io/otel/sdk v0.20.0 // indirect
go.opentelemetry.io/otel/sdk/export/metric v0.20.0 // indirect
go.opentelemetry.io/otel/sdk/metric v0.20.0 // indirect
go.opentelemetry.io/otel/trace v0.20.0 // indirect
go.opentelemetry.io/proto/otlp v0.7.0 // indirect
golang.org/x/tools v0.1.5 // indirect
golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
gopkg.in/cheggaaa/pb.v1 v1.0.28 // indirect
gopkg.in/natefinch/lumberjack.v2 v2.0.0 // indirect
)
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