Verify: only check post root if provided (#462)

Signed-off-by: Guillaume Ballet <3272758+gballet@users.noreply.github.com>

proof_ipa.go

@@ -638,41 +638,44 @@ func Verify(vp *VerkleProof, preStateRoot []byte, postStateRoot []byte, statedif
 	if err != nil {
 		return fmt.Errorf("error rebuilding the pre-tree from proof: %w", err)
 	}
-	// TODO this should not be necessary, remove it
-	// after the new proof generation code has stabilized.
-	for _, stemdiff := range statediff {
-		for _, suffixdiff := range stemdiff.SuffixDiffs {
-			var key [32]byte
-			copy(key[:31], stemdiff.Stem[:])
-			key[31] = suffixdiff.Suffix
 
-			val, err := pretree.Get(key[:], nil)
-			if err != nil {
-				return fmt.Errorf("could not find key %x in tree rebuilt from proof: %w", key, err)
-			}
-			if len(val) > 0 {
-				if !bytes.Equal(val, suffixdiff.CurrentValue[:]) {
-					return fmt.Errorf("could not find correct value at %x in tree rebuilt from proof: %x != %x", key, val, *suffixdiff.CurrentValue)
+	if len(postStateRoot) != 0 {
+		// TODO this should not be necessary, remove it
+		// after the new proof generation code has stabilized.
+		for _, stemdiff := range statediff {
+			for _, suffixdiff := range stemdiff.SuffixDiffs {
+				var key [32]byte
+				copy(key[:31], stemdiff.Stem[:])
+				key[31] = suffixdiff.Suffix
+
+				val, err := pretree.Get(key[:], nil)
+				if err != nil {
+					return fmt.Errorf("could not find key %x in tree rebuilt from proof: %w", key, err)
 				}
-			} else {
-				if suffixdiff.CurrentValue != nil && len(suffixdiff.CurrentValue) != 0 {
-					return fmt.Errorf("could not find correct value at %x in tree rebuilt from proof: %x != %x", key, val, *suffixdiff.CurrentValue)
+				if len(val) > 0 {
+					if !bytes.Equal(val, suffixdiff.CurrentValue[:]) {
+						return fmt.Errorf("could not find correct value at %x in tree rebuilt from proof: %x != %x", key, val, *suffixdiff.CurrentValue)
+					}
+				} else {
+					if suffixdiff.CurrentValue != nil && len(suffixdiff.CurrentValue) != 0 {
+						return fmt.Errorf("could not find correct value at %x in tree rebuilt from proof: %x != %x", key, val, *suffixdiff.CurrentValue)
+					}
 				}
 			}
 		}
-	}
 
-	// TODO: this is necessary to verify that the post-values are the correct ones.
-	// But all this can be avoided with a even faster way. The EVM block execution can
-	// keep track of the written keys, and compare that list with this post-values list.
-	// This can avoid regenerating the post-tree which is somewhat expensive.
-	posttree, err := PostStateTreeFromStateDiff(pretree, statediff)
-	if err != nil {
-		return fmt.Errorf("error rebuilding the post-tree from proof: %w", err)
-	}
-	regeneratedPostTreeRoot := posttree.Commitment().Bytes()
-	if !bytes.Equal(regeneratedPostTreeRoot[:], postStateRoot) {
-		return fmt.Errorf("post tree root mismatch: %x != %x", regeneratedPostTreeRoot, postStateRoot)
+		// TODO: this is necessary to verify that the post-values are the correct ones.
+		// But all this can be avoided with a even faster way. The EVM block execution can
+		// keep track of the written keys, and compare that list with this post-values list.
+		// This can avoid regenerating the post-tree which is somewhat expensive.
+		posttree, err := PostStateTreeFromStateDiff(pretree, statediff)
+		if err != nil {
+			return fmt.Errorf("error rebuilding the post-tree from proof: %w", err)
+		}
+		regeneratedPostTreeRoot := posttree.Commitment().Bytes()
+		if !bytes.Equal(regeneratedPostTreeRoot[:], postStateRoot) {
+			return fmt.Errorf("post tree root mismatch: %x != %x", regeneratedPostTreeRoot, postStateRoot)
+		}
 	}
 
 	return verifyVerkleProofWithPreState(proof, pretree)