/
verify.go
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/
verify.go
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//
// Copyright 2022 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package verify
import (
"bytes"
"context"
"encoding/base64"
"encoding/hex"
"encoding/json"
"errors"
"fmt"
"github.com/cyberphone/json-canonicalization/go/src/webpki.org/jsoncanonicalizer"
"github.com/sigstore/rekor/pkg/generated/client"
"github.com/sigstore/rekor/pkg/generated/client/tlog"
"github.com/sigstore/rekor/pkg/generated/models"
"github.com/sigstore/rekor/pkg/util"
"github.com/sigstore/sigstore/pkg/signature"
"github.com/sigstore/sigstore/pkg/signature/options"
"github.com/transparency-dev/merkle/proof"
"github.com/transparency-dev/merkle/rfc6962"
)
// ProveConsistency verifies consistency between an initial, trusted STH
// and a second new STH. Callers MUST verify signature on the STHs'.
func ProveConsistency(ctx context.Context, rClient *client.Rekor,
oldSTH *util.SignedCheckpoint, newSTH *util.SignedCheckpoint, treeID string) error {
oldTreeSize := int64(oldSTH.Size)
switch {
case oldTreeSize == int64(newSTH.Size):
if !bytes.Equal(oldSTH.Hash, newSTH.Hash) {
return errors.New("old root hash does not match STH hash")
}
case oldTreeSize < int64(newSTH.Size):
consistencyParams := tlog.NewGetLogProofParamsWithContext(ctx)
consistencyParams.FirstSize = &oldTreeSize // Root size at the old, or trusted state.
consistencyParams.LastSize = int64(newSTH.Size) // Root size at the new state to verify against.
consistencyParams.TreeID = &treeID
consistencyProof, err := rClient.Tlog.GetLogProof(consistencyParams)
if err != nil {
return err
}
var hashes [][]byte
for _, h := range consistencyProof.Payload.Hashes {
b, err := hex.DecodeString(h)
if err != nil {
return errors.New("error decoding consistency proof hashes")
}
hashes = append(hashes, b)
}
if err := proof.VerifyConsistency(rfc6962.DefaultHasher,
oldSTH.Size, newSTH.Size, hashes, oldSTH.Hash, newSTH.Hash); err != nil {
return err
}
case oldTreeSize > int64(newSTH.Size):
return errors.New("inclusion proof returned a tree size larger than the verified tree size")
}
return nil
}
// VerifyCurrentCheckpoint verifies the provided checkpoint by verifying consistency
// against a newly fetched Checkpoint.
//nolint
func VerifyCurrentCheckpoint(ctx context.Context, rClient *client.Rekor, verifier signature.Verifier,
oldSTH *util.SignedCheckpoint) error {
// The oldSTH should already be verified, but check for robustness.
if !oldSTH.Verify(verifier) {
return errors.New("signature on old tree head did not verify")
}
// Get and verify against the current STH.
infoParams := tlog.NewGetLogInfoParamsWithContext(ctx)
result, err := rClient.Tlog.GetLogInfo(infoParams)
if err != nil {
return err
}
logInfo := result.GetPayload()
sth := util.SignedCheckpoint{}
if err := sth.UnmarshalText([]byte(*logInfo.SignedTreeHead)); err != nil {
return err
}
// Verify the signature on the SignedCheckpoint.
if !sth.Verify(verifier) {
return errors.New("signature on tree head did not verify")
}
// Now verify consistency up to the STH.
return ProveConsistency(ctx, rClient, oldSTH, &sth, *logInfo.TreeID)
}
// VerifyInclusion verifies an entry's inclusion proof. Clients MUST either verify
// the root hash against a new STH (via VerifyCurrentCheckpoint) or against a
// trusted, existing STH (via ProveConsistency).
//nolint
func VerifyInclusion(ctx context.Context, e *models.LogEntryAnon) error {
if e.Verification == nil || e.Verification.InclusionProof == nil {
return errors.New("inclusion proof not provided")
}
hashes := [][]byte{}
for _, h := range e.Verification.InclusionProof.Hashes {
hb, _ := hex.DecodeString(h)
hashes = append(hashes, hb)
}
rootHash, err := hex.DecodeString(*e.Verification.InclusionProof.RootHash)
if err != nil {
return err
}
// Verify the inclusion proof.
entryBytes, err := base64.StdEncoding.DecodeString(e.Body.(string))
if err != nil {
return err
}
leafHash := rfc6962.DefaultHasher.HashLeaf(entryBytes)
if err := proof.VerifyInclusion(rfc6962.DefaultHasher, uint64(*e.Verification.InclusionProof.LogIndex),
uint64(*e.Verification.InclusionProof.TreeSize), leafHash, hashes, rootHash); err != nil {
return err
}
return nil
}
// VerifySignedEntryTimestamp verifies the entry's SET against the provided
// public key.
//nolint
func VerifySignedEntryTimestamp(ctx context.Context, e *models.LogEntryAnon, verifier signature.Verifier) error {
if e.Verification == nil {
return fmt.Errorf("missing verification")
}
if e.Verification.SignedEntryTimestamp == nil {
return fmt.Errorf("signature missing")
}
type bundle struct {
Body interface{} `json:"body"`
IntegratedTime int64 `json:"integratedTime"`
// Note that this is the virtual index.
LogIndex int64 `json:"logIndex"`
LogID string `json:"logID"`
}
bundlePayload := bundle{
Body: e.Body,
IntegratedTime: *e.IntegratedTime,
LogIndex: *e.LogIndex,
LogID: *e.LogID,
}
contents, err := json.Marshal(bundlePayload)
if err != nil {
return fmt.Errorf("marshaling bundle: %w", err)
}
canonicalized, err := jsoncanonicalizer.Transform(contents)
if err != nil {
return fmt.Errorf("canonicalizing bundle: %w", err)
}
// verify the SET against the public key
if err := verifier.VerifySignature(bytes.NewReader(e.Verification.SignedEntryTimestamp),
bytes.NewReader(canonicalized), options.WithContext(ctx)); err != nil {
return fmt.Errorf("unable to verify bundle: %w", err)
}
return nil
}
// VerifyLogEntry performs verification of a LogEntry given a Rekor verifier.
// Performs inclusion proof verification up to a verified root hash and
// SignedEntryTimestamp verification.
//nolint
func VerifyLogEntry(ctx context.Context, e *models.LogEntryAnon, verifier signature.Verifier) error {
// Verify the inclusion proof using the body's leaf hash.
if err := VerifyInclusion(ctx, e); err != nil {
return err
}
// TODO: If/when we return an STH in the response, verify that too, against an
// optional known STH as well.
// See https://github.com/sigstore/rekor/issues/988
// Verify the Signed Entry Timestamp.
if err := VerifySignedEntryTimestamp(ctx, e, verifier); err != nil {
return err
}
return nil
}