perf: cache verifiers to eliminate duplicate Idemix proofs

Signed-off-by: AkramBitar <akram@il.ibm.com>

Author: AkramBitar

token/core/zkatdlog/nogh/v1/validator/validator_extra_test.go

@@ -444,3 +444,74 @@ func TestDeserializeActionsErrors(t *testing.T) {
 	_, _, err = ad.DeserializeActions(tr)
 	require.Error(t, err)
 }
+
+// TestTransferVerifierCache tests that when multiple inputs have the same owner,
+// the verifier is only deserialized once (cache hit)
+func TestTransferVerifierCache(t *testing.T) {
+	ctx := context.Background()
+
+	// Create a transfer action with 3 inputs, where 2 have the same owner
+	sameOwner := []byte("same-owner-identity")
+	differentOwner := []byte("different-owner-identity")
+
+	transferAction := &transfer.Action{
+		Inputs: []*transfer.ActionInput{
+			{Token: &token.Token{Owner: sameOwner}},      // Input 0: same owner
+			{Token: &token.Token{Owner: sameOwner}},      // Input 1: same owner (should hit cache)
+			{Token: &token.Token{Owner: differentOwner}}, // Input 2: different owner
+		},
+		Outputs: []*token.Token{
+			{Owner: []byte("output-owner")},
+		},
+	}
+
+	// Track deserializer calls
+	deserializerCallCount := 0
+	ownerCallsByIdentity := make(map[string]int)
+
+	mockDes := &mock3.Deserializer{}
+	mockDes.GetOwnerVerifierCalls(func(ctx context.Context, id driver.Identity) (driver.Verifier, error) {
+		deserializerCallCount++
+		key := string(id)
+		ownerCallsByIdentity[key]++
+		return &mock3.Verifier{}, nil
+	})
+
+	mockSigProv := &mockSignatureProvider{
+		HasBeenSignedByFunc: func(ctx context.Context, id driver.Identity, verifier driver.Verifier) ([]byte, error) {
+			return []byte("signature"), nil
+		},
+	}
+
+	validatorCtx := &validator.Context{
+		Logger:            &logging.MockLogger{},
+		TransferAction:    transferAction,
+		Deserializer:      mockDes,
+		SignatureProvider: mockSigProv,
+		PP:                &v1.PublicParams{},
+	}
+
+	// Execute validation
+	err := validator.TransferSignatureValidate(ctx, validatorCtx)
+	require.NoError(t, err)
+
+	// Verify results - WITH cache implementation
+	t.Logf("Total GetOwnerVerifier calls: %d", deserializerCallCount)
+	t.Logf("Calls for same owner: %d", ownerCallsByIdentity[string(sameOwner)])
+	t.Logf("Calls for different owner: %d", ownerCallsByIdentity[string(differentOwner)])
+
+	// With verifier cache: deserializer is called only once per unique owner
+	// Expected: 2 calls total (once for sameOwner, once for differentOwner)
+	require.Equal(t, 2, deserializerCallCount, "With cache: should call deserializer only for unique owners")
+	require.Equal(t, 1, ownerCallsByIdentity[string(sameOwner)], "With cache: same owner called only once")
+	require.Equal(t, 1, ownerCallsByIdentity[string(differentOwner)], "Different owner called once")
+
+	// Calculate cache effectiveness
+	uniqueOwners := 2
+	totalInputs := 3
+	cacheHits := totalInputs - uniqueOwners
+	cacheHitRate := float64(cacheHits) / float64(totalInputs) * 100
+
+	t.Logf("Cache hit rate: %.1f%% (%d cache hits out of %d inputs)",
+		cacheHitRate, cacheHits, totalInputs)
+}

token/core/zkatdlog/nogh/v1/validator/validator_transfer.go

@@ -36,6 +36,10 @@ func TransferSignatureValidate(c context.Context, ctx *Context) error {
 		return ErrInvalidInputs
 	}
 
+	// Cache verifiers within this transaction to avoid redundant verifyProof() calls
+	// for inputs with the same owner identity
+	verifierCache := make(map[string]driver.Verifier)
+
 	var isRedeem bool
 	var inputToken []*token.Token
 	for i, in := range ctx.TransferAction.Inputs {
@@ -44,10 +48,19 @@ func TransferSignatureValidate(c context.Context, ctx *Context) error {
 
 		// check sender signature
 		ctx.Logger.Debugf("check sender [%d][%s]", i, driver.Identity(tok.Owner).UniqueID())
-		verifier, err := ctx.Deserializer.GetOwnerVerifier(c, tok.Owner)
-		if err != nil {
-			return errors.Wrapf(err, "failed deserializing owner [%d][%v][%s]", i, in, driver.Identity(tok.Owner))
+
+		// Check cache first to avoid redundant expensive verifyProof() calls
+		ownerKey := driver.Identity(tok.Owner).UniqueID()
+		verifier, cached := verifierCache[ownerKey]
+		if !cached {
+			var err error
+			verifier, err = ctx.Deserializer.GetOwnerVerifier(c, tok.Owner)
+			if err != nil {
+				return errors.Wrapf(err, "failed deserializing owner [%d][%v][%s]", i, in, driver.Identity(tok.Owner))
+			}
+			verifierCache[ownerKey] = verifier
 		}
+
 		ctx.Logger.Debugf("signature verification [%d][%v][%s]", i, in, driver.Identity(tok.Owner).UniqueID())
 		sigma, err := ctx.SignatureProvider.HasBeenSignedBy(c, tok.Owner, verifier)
 		if err != nil {
@@ -132,10 +145,11 @@ func TransferZKProofValidate(c context.Context, ctx *Context) error {
 		in[i] = tok.Data
 	}
 
-	if err := transfer.NewVerifier(
+	err := transfer.NewVerifier(
 		in,
 		ctx.TransferAction.GetOutputCommitments(),
-		ctx.PP).Verify(ctx.TransferAction.GetProof()); err != nil {
+		ctx.PP).Verify(ctx.TransferAction.GetProof())
+	if err != nil {
 		return errors.Join(err, ErrInvalidZKP)
 	}