crypto/kzg4844: add helpers for versioned blob hashes (ethereum#28827) (#876)

The code to compute a versioned hash was duplicated a couple times, and also had a small
issue: if we ever change params.BlobTxHashVersion, it will most likely also cause changes
to the actual hash computation. So it's a bit useless to have this constant in params.

Co-authored-by: Felix Lange <[email protected]>

Author: 0xmountaintop

core/state_transition.go

@@ -26,6 +26,7 @@ import (
 	cmath "github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/crypto/kzg4844"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 )
@@ -369,9 +370,8 @@ func (st *StateTransition) preCheck() error {
 			return errors.New("blob transaction missing blob hashes")
 		}
 		for i, hash := range msg.BlobHashes {
-			if hash[0] != params.BlobTxHashVersion {
-				return fmt.Errorf("blob %d hash version mismatch (have %d, supported %d)",
-					i, hash[0], params.BlobTxHashVersion)
+			if !kzg4844.IsValidVersionedHash(hash[:]) {
+				return fmt.Errorf("blob %d has invalid hash version", i)
 			}
 		}
 	}

core/txpool/blobpool/blobpool_test.go

@@ -51,21 +51,9 @@ var (
 	emptyBlob          = kzg4844.Blob{}
 	emptyBlobCommit, _ = kzg4844.BlobToCommitment(emptyBlob)
 	emptyBlobProof, _  = kzg4844.ComputeBlobProof(emptyBlob, emptyBlobCommit)
-	emptyBlobVHash     = blobHash(emptyBlobCommit)
+	emptyBlobVHash     = kzg4844.CalcBlobHashV1(sha256.New(), &emptyBlobCommit)
 )
 
-func blobHash(commit kzg4844.Commitment) common.Hash {
-	hasher := sha256.New()
-	hasher.Write(commit[:])
-	hash := hasher.Sum(nil)
-
-	var vhash common.Hash
-	vhash[0] = params.BlobTxHashVersion
-	copy(vhash[1:], hash[1:])
-
-	return vhash
-}
-
 // Chain configuration with Cancun enabled.
 //
 // TODO(karalabe): replace with params.MainnetChainConfig after Cancun.

core/txpool/validation.go

@@ -144,17 +144,10 @@ func validateBlobSidecar(hashes []common.Hash, sidecar *types.BlobTxSidecar) err
 	// Blob quantities match up, validate that the provers match with the
 	// transaction hash before getting to the cryptography
 	hasher := sha256.New()
-	for i, want := range hashes {
-		hasher.Write(sidecar.Commitments[i][:])
-		hash := hasher.Sum(nil)
-		hasher.Reset()
-
-		var vhash common.Hash
-		vhash[0] = params.BlobTxHashVersion
-		copy(vhash[1:], hash[1:])
-
-		if vhash != want {
-			return fmt.Errorf("blob %d: computed hash %#x mismatches transaction one %#x", i, vhash, want)
+	for i, vhash := range hashes {
+		computed := kzg4844.CalcBlobHashV1(hasher, &sidecar.Commitments[i])
+		if vhash != computed {
+			return fmt.Errorf("blob %d: computed hash %#x mismatches transaction one %#x", i, computed, vhash)
 		}
 	}
 	// Blob commitments match with the hashes in the transaction, verify the

core/types/tx_blob.go

@@ -61,9 +61,10 @@ type BlobTxSidecar struct {
 
 // BlobHashes computes the blob hashes of the given blobs.
 func (sc *BlobTxSidecar) BlobHashes() []common.Hash {
+	hasher := sha256.New()
 	h := make([]common.Hash, len(sc.Commitments))
 	for i := range sc.Blobs {
-		h[i] = blobHash(&sc.Commitments[i])
+		h[i] = kzg4844.CalcBlobHashV1(hasher, &sc.Commitments[i])
 	}
 	return h
 }
@@ -235,12 +236,3 @@ func (tx *BlobTx) decode(input []byte) error {
 	}
 	return nil
 }
-
-func blobHash(commit *kzg4844.Commitment) common.Hash {
-	hasher := sha256.New()
-	hasher.Write(commit[:])
-	var vhash common.Hash
-	hasher.Sum(vhash[:0])
-	vhash[0] = params.BlobTxHashVersion
-	return vhash
-}

crypto/kzg4844/kzg4844.go

@@ -20,6 +20,7 @@ package kzg4844
 import (
 	"embed"
 	"errors"
+	"hash"
 	"sync/atomic"
 )
 
@@ -108,3 +109,21 @@ func VerifyBlobProof(blob Blob, commitment Commitment, proof Proof) error {
 	}
 	return gokzgVerifyBlobProof(blob, commitment, proof)
 }
+
+// CalcBlobHashV1 calculates the 'versioned blob hash' of a commitment.
+// The given hasher must be a sha256 hash instance, otherwise the result will be invalid!
+func CalcBlobHashV1(hasher hash.Hash, commit *Commitment) (vh [32]byte) {
+	if hasher.Size() != 32 {
+		panic("wrong hash size")
+	}
+	hasher.Reset()
+	hasher.Write(commit[:])
+	hasher.Sum(vh[:0])
+	vh[0] = 0x01 // version
+	return vh
+}
+
+// IsValidVersionedHash checks that h is a structurally-valid versioned blob hash.
+func IsValidVersionedHash(h []byte) bool {
+	return len(h) == 32 && h[0] == 0x01
+}

eth/downloader/queue.go

@@ -29,6 +29,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/prque"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/crypto/kzg4844"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
 	"github.com/ethereum/go-ethereum/params"
@@ -810,7 +811,7 @@ func (q *queue) DeliverBodies(id string, txLists [][]*types.Transaction, txListH
 					return errInvalidBody
 				}
 				for _, hash := range tx.BlobHashes() {
-					if hash[0] != params.BlobTxHashVersion {
+					if !kzg4844.IsValidVersionedHash(hash[:]) {
 						return errInvalidBody
 					}
 				}

params/protocol_params.go

@@ -166,7 +166,6 @@ const (
 
 	BlobTxBytesPerFieldElement         = 32      // Size in bytes of a field element
 	BlobTxFieldElementsPerBlob         = 4096    // Number of field elements stored in a single data blob
-	BlobTxHashVersion                  = 0x01    // Version byte of the commitment hash
 	BlobTxBlobGasPerBlob               = 1 << 17 // Gas consumption of a single data blob (== blob byte size)
 	BlobTxMinBlobGasprice              = 1       // Minimum gas price for data blobs
 	BlobTxBlobGaspriceUpdateFraction   = 3338477 // Controls the maximum rate of change for blob gas price