KZG Commitment inclusion proof verifier (#13174)

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

consensus-types/blocks/kzg.go

@@ -15,12 +15,39 @@ const (
 	bodyLength    = 12 // The number of elements in the BeaconBlockBody Container
 	logBodyLength = 4  // The log 2 of bodyLength
 	kzgPosition   = 11 // The index of the KZG commitment list in the Body
+	KZGOffset     = 54 * field_params.MaxBlobCommitmentsPerBlock
 )
 
 var (
-	errInvalidIndex = errors.New("index out of bounds")
+	errInvalidIndex          = errors.New("index out of bounds")
+	errInvalidBodyRoot       = errors.New("invalid Beacon Block Body root")
+	errInvalidInclusionProof = errors.New("invalid KZG commitment inclusion proof")
 )
 
+// VerifyKZGIncusionProof verifies the Merkle proof in a Blob sidecar against
+// the beacon block body root.
+func VerifyKZGInclusionProof(blob ROBlob) error {
+	if blob.SignedBlockHeader == nil {
+		return errNilBlockHeader
+	}
+	if blob.SignedBlockHeader.Header == nil {
+		return errNilBlockHeader
+	}
+	root := blob.SignedBlockHeader.Header.BodyRoot
+	if len(root) != field_params.RootLength {
+		return errInvalidBodyRoot
+	}
+	chunks := make([][32]byte, 2)
+	copy(chunks[0][:], blob.KzgCommitment)
+	copy(chunks[1][:], blob.KzgCommitment[field_params.RootLength:])
+	gohashtree.HashChunks(chunks, chunks)
+	verified := trie.VerifyMerkleProof(root, chunks[0][:], blob.Index+KZGOffset, blob.CommitmentInclusionProof)
+	if !verified {
+		return errInvalidInclusionProof
+	}
+	return nil
+}
+
 // MerkleProofKZGCommitment constructs a Merkle proof of inclusion of the KZG
 // commitment of index `index` into the Beacon Block with the given `body`
 func MerkleProofKZGCommitment(body interfaces.ReadOnlyBeaconBlockBody, index int) ([][]byte, error) {

consensus-types/blocks/kzg_test.go

@@ -128,3 +128,67 @@ func Benchmark_MerkleProofKZGCommitment(b *testing.B) {
 		require.NoError(b, err)
 	}
 }
+
+func Test_VerifyKZGInclusionProof(t *testing.T) {
+	kzgs := make([][]byte, 3)
+	kzgs[0] = make([]byte, 48)
+	_, err := rand.Read(kzgs[0])
+	require.NoError(t, err)
+	kzgs[1] = make([]byte, 48)
+	_, err = rand.Read(kzgs[1])
+	require.NoError(t, err)
+	kzgs[2] = make([]byte, 48)
+	_, err = rand.Read(kzgs[2])
+	require.NoError(t, err)
+	pbBody := &ethpb.BeaconBlockBodyDeneb{
+		SyncAggregate: &ethpb.SyncAggregate{
+			SyncCommitteeBits:      make([]byte, fieldparams.SyncAggregateSyncCommitteeBytesLength),
+			SyncCommitteeSignature: make([]byte, fieldparams.BLSSignatureLength),
+		},
+		ExecutionPayload: &enginev1.ExecutionPayloadDeneb{
+			ParentHash:    make([]byte, fieldparams.RootLength),
+			FeeRecipient:  make([]byte, 20),
+			StateRoot:     make([]byte, fieldparams.RootLength),
+			ReceiptsRoot:  make([]byte, fieldparams.RootLength),
+			LogsBloom:     make([]byte, 256),
+			PrevRandao:    make([]byte, fieldparams.RootLength),
+			BaseFeePerGas: make([]byte, fieldparams.RootLength),
+			BlockHash:     make([]byte, fieldparams.RootLength),
+			Transactions:  make([][]byte, 0),
+			ExtraData:     make([]byte, 0),
+		},
+		Eth1Data: &ethpb.Eth1Data{
+			DepositRoot: make([]byte, fieldparams.RootLength),
+			BlockHash:   make([]byte, fieldparams.RootLength),
+		},
+		BlobKzgCommitments: kzgs,
+	}
+
+	body, err := NewBeaconBlockBody(pbBody)
+	require.NoError(t, err)
+	root, err := body.HashTreeRoot()
+	require.NoError(t, err)
+	index := 1
+	proof, err := MerkleProofKZGCommitment(body, index)
+	require.NoError(t, err)
+
+	header := &ethpb.BeaconBlockHeader{
+		BodyRoot:   root[:],
+		ParentRoot: make([]byte, 32),
+		StateRoot:  make([]byte, 32),
+	}
+	signedHeader := &ethpb.SignedBeaconBlockHeader{
+		Header: header,
+	}
+	sidecar := &ethpb.BlobSidecar{
+		Index:                    uint64(index),
+		KzgCommitment:            kzgs[index],
+		CommitmentInclusionProof: proof,
+		SignedBlockHeader:        signedHeader,
+	}
+	blob, err := NewROBlob(sidecar)
+	require.NoError(t, err)
+	require.NoError(t, VerifyKZGInclusionProof(blob))
+	proof[2] = make([]byte, 32)
+	require.ErrorIs(t, errInvalidInclusionProof, VerifyKZGInclusionProof(blob))
+}

testing/spectest/shared/common/merkle_proof/single_merkle_proof.go

@@ -18,8 +18,6 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/testing/util"
 )
 
-const kzgOffset = 54 * field_params.MaxBlobCommitmentsPerBlock
-
 // SingleMerkleProof is the format used to read spectest Merkle Proof test data.
 type SingleMerkleProof struct {
 	Leaf      string   `json:"leaf"`
@@ -83,10 +81,10 @@ func runSingleMerkleProofTests(t *testing.T, config, forkOrPhase string, unmarsh
 				if err != nil {
 					return
 				}
-				if index < kzgOffset || index > kzgOffset+field_params.MaxBlobsPerBlock {
+				if index < consensus_blocks.KZGOffset || index > consensus_blocks.KZGOffset+field_params.MaxBlobsPerBlock {
 					return
 				}
-				localProof, err := consensus_blocks.MerkleProofKZGCommitment(body, int(index-kzgOffset))
+				localProof, err := consensus_blocks.MerkleProofKZGCommitment(body, int(index-consensus_blocks.KZGOffset))
 				require.NoError(t, err)
 				require.Equal(t, len(branch), len(localProof))
 				for i, root := range localProof {