Verify key length in range proofs (#176)

## Why this should be merged

This enforces an assumption that is currently made by
`VerifyRangeProof`. If a key is a prefix of another key, the current
code can panic.

## How this works

Enforces all keys have the same length.

## How this was tested

Added a unit test.

trie/proof.go

@@ -487,6 +487,10 @@ func VerifyRangeProof(rootHash common.Hash, firstKey []byte, keys [][]byte, valu
 	}
 	// Ensure the received batch is monotonic increasing and contains no deletions
 	for i := 0; i < len(keys)-1; i++ {
+		// See: https://github.com/ava-labs/coreth/issues/907
+		if len(keys[i]) != len(keys[i+1]) {
+			return false, errKeysHaveDifferentLengths
+		}
 		if bytes.Compare(keys[i], keys[i+1]) >= 0 {
 			return false, errors.New("range is not monotonically increasing")
 		}

trie/proof.libevm.go

@@ -0,0 +1,23 @@
+// Copyright 2025 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package trie
+
+import (
+	"errors"
+)
+
+var errKeysHaveDifferentLengths = errors.New("keys have different lengths")

trie/proof.libevm_test.go

@@ -0,0 +1,48 @@
+// Copyright 2025 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package trie
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/ava-labs/libevm/common"
+)
+
+func TestRangeProofKeysWithDifferentLengths(t *testing.T) {
+	var (
+		root  = common.HexToHash("0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef")
+		start = common.Hex2Bytes("0000000000000000000000000000000000000000000000000000000000000000")
+		keys  = [][]byte{
+			common.Hex2Bytes("1000000000000000000000000000000"),
+			common.Hex2Bytes("1000000000000000000000000000000000000000000000000000000000000000"),
+		}
+		values = [][]byte{
+			common.Hex2Bytes("02"),
+			common.Hex2Bytes("03"),
+		}
+	)
+	_, err := VerifyRangeProof(
+		root,
+		start,
+		keys,
+		values,
+		nil, // force it to use stacktrie
+	)
+	require.ErrorIs(t, err, errKeysHaveDifferentLengths)
+}