crypto: add go-based BatchVerifier implementation (algorand#6440)

This adds a pure-Go ed25519 BatchVerifier implementation based on the ed25519consensus library, with additional checks to preserve our ed25519 validation criteria, last updated in algorand#3031.

Like our libsodium batch verification implementation, the IsCanonicalY check here is also based on the "Taming the Many EdDSAs" paper in https://eprint.iacr.org/2020/1244

New tests added to compare ed25519 criteria results match our existing libsodium- and ed25519-donna-based batch verification implementation (from algorand#3031 and defined in algorandfoundation/specs#60). New test helpers run test vectors with different batch sizes, taken from
- 12 edge cases from "Taming the many EdDSAs" Appendix C, Table 6c, also used in our libsodium fork's tests in batch verification: add ed25519 batch verification implementation algorand#3031
- 1025 successful cases from our libsodium fork's tests, also added in batch verification: add ed25519 batch verification implementation algorand#3031.
- 196 edge cases used to draw the 14x14 grid visualizations from the blog post "It's 255:19AM. Do you know what your validation criteria are?" and used in ed25519consensus
- 768 edge cases from the Go crypto package's crypto/ed25519/ed25519vectors_test.go

Author: cce

crypto/batchverifier.go

@@ -73,16 +73,35 @@ func ed25519_randombytes_unsafe(p unsafe.Pointer, len C.size_t) {
 const minBatchVerifierAlloc = 16
 const useSingleVerifierDefault = true
 
-// MakeBatchVerifier creates a BatchVerifier instance with the provided options.
+// ed25519BatchVerifierFactory is the global singleton used for batch signature verification.
+// By default it uses the libsodium implementation. This can be changed during initialization
+// (e.g., by the config package when algod loads) to use the ed25519consensus implementation.
+var ed25519BatchVerifierFactory func(hint int) BatchVerifier = makeLibsodiumBatchVerifier
+
+// SetEd25519BatchVerifier allows the config package to switch the implementation
+// at startup based on configuration. Pass true to use ed25519consensus, false for libsodium.
+func SetEd25519BatchVerifier(useEd25519Consensus bool) {
+	if useEd25519Consensus {
+		ed25519BatchVerifierFactory = makeEd25519ConsensusBatchVerifier
+	} else {
+		ed25519BatchVerifierFactory = makeLibsodiumBatchVerifier
+	}
+}
+
+// MakeBatchVerifier creates a BatchVerifier instance.
 func MakeBatchVerifier() BatchVerifier {
-	return MakeBatchVerifierWithHint(minBatchVerifierAlloc)
+	return ed25519BatchVerifierFactory(minBatchVerifierAlloc)
 }
 
-// MakeBatchVerifierWithHint creates a cgoBatchVerifier instance. This function pre-allocates
-// amount of free space to enqueue signatures without expanding
+// MakeBatchVerifierWithHint creates a BatchVerifier instance. This function pre-allocates
+// space to enqueue signatures without expanding.
 func MakeBatchVerifierWithHint(hint int) BatchVerifier {
+	return ed25519BatchVerifierFactory(hint)
+}
+
+func makeLibsodiumBatchVerifier(hint int) BatchVerifier {
 	// preallocate enough storage for the expected usage. We will reallocate as needed.
-	if hint < minBatchVerifierAlloc {
+	if hint <= 0 {
 		hint = minBatchVerifierAlloc
 	}
 	return &cgoBatchVerifier{
@@ -152,7 +171,7 @@ func (b *cgoBatchVerifier) VerifyWithFeedback() (failed []bool, err error) {
 	}
 	allValid, failed := cgoBatchVerificationImpl(messages, msgLengths, b.publicKeys, b.signatures)
 	if allValid {
-		return failed, nil
+		return nil, nil
 	}
 	return failed, ErrBatchHasFailedSigs
 }
@@ -170,7 +189,7 @@ func (b *cgoBatchVerifier) singleVerify() (failed []bool, err error) {
 	if containsFailed {
 		return failed, ErrBatchHasFailedSigs
 	}
-	return failed, nil
+	return nil, nil
 }
 
 // cgoBatchVerificationImpl invokes the ed25519 batch verification algorithm.
@@ -185,18 +204,26 @@ func cgoBatchVerificationImpl(messages []byte, msgLengths []uint64, publicKeys [
 	signatures2D := make([]*C.uchar, numberOfSignatures)
 
 	// call the batch verifier
+	// Use unsafe.SliceData to safely get pointers to underlying arrays
 	allValid := C.ed25519_batch_wrapper(
-		&messages2D[0], &publicKeys2D[0], &signatures2D[0],
-		(*C.uchar)(&messages[0]),
-		(*C.ulonglong)(&msgLengths[0]),
-		(*C.uchar)(&publicKeys[0][0]),
-		(*C.uchar)(&signatures[0][0]),
+		(**C.uchar)(unsafe.SliceData(messages2D)),
+		(**C.uchar)(unsafe.SliceData(publicKeys2D)),
+		(**C.uchar)(unsafe.SliceData(signatures2D)),
+		(*C.uchar)(unsafe.SliceData(messages)),
+		(*C.ulonglong)(unsafe.SliceData(msgLengths)),
+		(*C.uchar)(unsafe.SliceData(publicKeys[0][:])),
+		(*C.uchar)(unsafe.SliceData(signatures[0][:])),
 		C.size_t(numberOfSignatures),
-		(*C.int)(&valid[0]))
+		(*C.int)(unsafe.SliceData(valid)))
+
+	if allValid == 0 { // all signatures valid
+		return true, nil
+	}
 
+	// not all signatures valid, identify the failed signatures
 	failed = make([]bool, numberOfSignatures)
 	for i := 0; i < numberOfSignatures; i++ {
 		failed[i] = (valid[i] == 0)
 	}
-	return allValid == 0, failed
+	return false, failed
 }

crypto/batchverifier_bench_test.go

@@ -0,0 +1,123 @@
+// Copyright (C) 2019-2025 Algorand, Inc.
+// This file is part of go-algorand
+//
+// go-algorand is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// go-algorand is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with go-algorand.  If not, see <https://www.gnu.org/licenses/>.
+
+package crypto
+
+import (
+	cryptorand "crypto/rand"
+	"io"
+	"testing"
+
+	"github.com/algorand/go-algorand/test/partitiontest"
+	"github.com/stretchr/testify/require"
+)
+
+func randSignedMsg(t testing.TB, r io.Reader) (SignatureVerifier, Hashable, Signature) {
+	mlen := 100
+	msg := TestingHashable{data: make([]byte, mlen)}
+	n, err := r.Read(msg.data)
+	require.NoError(t, err)
+	require.Equal(t, n, mlen)
+	var s Seed
+	n, err = r.Read(s[:])
+	require.NoError(t, err)
+	require.Equal(t, 32, n)
+	secrets := GenerateSignatureSecrets(s)
+	return secrets.SignatureVerifier, msg, secrets.Sign(msg)
+}
+
+// BenchmarkBatchVerifierImpls benchmarks different batch verification implementations
+// with realistic batch sizes (100 batches of 64 signatures each)
+func BenchmarkBatchVerifierImpls(b *testing.B) {
+	partitiontest.PartitionTest(b)
+
+	numBatches := 100
+	batchSize := 64
+	msgs := make([][]Hashable, numBatches)
+	pks := make([][]SignatureVerifier, numBatches)
+	sigs := make([][]Signature, numBatches)
+	r := cryptorand.Reader
+	for i := 0; i < numBatches; i++ {
+		for j := 0; j < batchSize; j++ {
+			pk, msg, sig := randSignedMsg(b, r)
+			msgs[i] = append(msgs[i], msg)
+			pks[i] = append(pks[i], pk)
+			sigs[i] = append(sigs[i], sig)
+		}
+	}
+
+	b.Log("running with", b.N, "iterations using", len(msgs), "batches of", batchSize, "signatures")
+	runImpl := func(b *testing.B, bv BatchVerifier,
+		msgs [][]Hashable, pks [][]SignatureVerifier, sigs [][]Signature) {
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			batchIdx := i % numBatches
+			for j := range msgs[batchIdx] {
+				bv.EnqueueSignature(pks[batchIdx][j], msgs[batchIdx][j], sigs[batchIdx][j])
+			}
+			require.NoError(b, bv.Verify())
+		}
+	}
+
+	b.Run("libsodium_single", func(b *testing.B) {
+		bv := makeLibsodiumBatchVerifier(batchSize)
+		bv.(*cgoBatchVerifier).useSingle = true
+		runImpl(b, bv, msgs, pks, sigs)
+	})
+	b.Run("libsodium_batch", func(b *testing.B) {
+		bv := makeLibsodiumBatchVerifier(batchSize)
+		bv.(*cgoBatchVerifier).useSingle = false
+		runImpl(b, bv, msgs, pks, sigs)
+	})
+	b.Run("ed25519consensus", func(b *testing.B) {
+		bv := makeEd25519ConsensusBatchVerifier(batchSize)
+		runImpl(b, bv, msgs, pks, sigs)
+	})
+}
+
+func BenchmarkCanonicalityCheck(b *testing.B) {
+	partitiontest.PartitionTest(b)
+
+	const maxN = 10000
+	pubkeys := make([]SignatureVerifier, maxN)
+	sigs := make([]Signature, maxN)
+	for i := 0; i < maxN; i++ {
+		var s Seed
+		RandBytes(s[:])
+		sigSecrets := GenerateSignatureSecrets(s)
+		pubkeys[i] = sigSecrets.SignatureVerifier
+		msg := randString()
+		sigs[i] = sigSecrets.Sign(msg)
+	}
+
+	b.Run("pubkey_check", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			_ = isCanonicalPoint(pubkeys[i%maxN])
+		}
+	})
+
+	b.Run("signature_R_check", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			_ = isCanonicalPoint([32]byte(sigs[i%maxN][:32]))
+		}
+	})
+
+	b.Run("both_checks", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			_ = !isCanonicalPoint(pubkeys[i%maxN]) || !isCanonicalPoint([32]byte(sigs[i%maxN][:32]))
+		}
+	})
+}