fix: skip quadratic base58 decode outside the 64-byte signature length band

Only 64..88 base58 chars can decode to 64 bytes, so gating the decode on that
band is output-equivalent. Also cap tx_hash on the unauthenticated InboundKeys
query.

Author: 0xNilesh

utils/canonical.go

@@ -20,6 +20,18 @@ const (
 
 const base58Alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
 
+// A base58-encoded 64-byte Solana signature is always 64..88 characters: 88 is
+// ceil(512 / log2(58)) for a full-range value, and 64 is the all-zero case
+// (each leading zero byte encodes as one '1'). Outside that band the decode can
+// never produce 64 bytes, so its result would be discarded — see
+// canonicalizeSolanaTxHash. mr-tron/base58's decoder is quadratic (for each of
+// n characters it walks ceil(n/4) limbs), so decoding attacker-supplied strings
+// only to throw the result away is an unmetered CPU sink on public query paths.
+const (
+	solanaSigBase58MinLen = 64
+	solanaSigBase58MaxLen = 88
+)
+
 // CAIP2Namespace returns the namespace component of a CAIP-2 chain id
 // ("eip155:1" → "eip155"). Returns "" when the id has no namespace.
 func CAIP2Namespace(chain string) string {
@@ -119,8 +131,13 @@ func canonicalizeSolanaTxHash(s string) (string, error) {
 	if strings.HasPrefix(canon, "0x") {
 		return canon, nil
 	}
-	if raw, decErr := base58.Decode(canon); decErr == nil && len(raw) == 64 {
-		return "0x" + hex.EncodeToString(raw), nil
+	// Only attempt the decode for lengths that can actually yield 64 bytes.
+	// This is output-equivalent for every possible input: a string outside the
+	// band already falls through to `return canon` below, decode or not.
+	if n := len(canon); n >= solanaSigBase58MinLen && n <= solanaSigBase58MaxLen {
+		if raw, decErr := base58.Decode(canon); decErr == nil && len(raw) == 64 {
+			return "0x" + hex.EncodeToString(raw), nil
+		}
 	}
 	return canon, nil
 }

utils/canonical_test.go

@@ -1,23 +1,28 @@
 package utils_test
 
 import (
+	"encoding/hex"
+	"math/rand"
+	"strings"
 	"testing"
+	"time"
 
+	"github.com/mr-tron/base58"
 	"github.com/stretchr/testify/require"
 
 	"github.com/pushchain/push-chain-node/utils"
 )
 
 const (
-	eip55Addr  = "0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed"
-	lowerAddr  = "0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed"
-	upperAddr  = "0X5AAEB6053F3E94C9B9A09F33669435E7EF1BEAED"
-	noPfxAddr  = "5aaeb6053f3e94c9b9a09f33669435e7ef1beaed"
-	mixedHash  = "0xB28F49668e7e76dc96D7aaBE5b7f63FEcfbd1c3574774c05e8204e749fd96fbd"
-	lowerHash  = "0xb28f49668e7e76dc96d7aabe5b7f63fecfbd1c3574774c05e8204e749fd96fbd"
-	noPfxHash  = "b28f49668e7e76dc96d7aabe5b7f63fecfbd1c3574774c05e8204e749fd96fbd"
-	solPubkey  = "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v"
-	solSig     = "5j7s6NiJS3JAkvgkoc18WVAsiSaci2pxB2A6ueCJP4tprA2TFg9wSyTLeYouxPBJEMzJinENTkpA52YStRW5Dia7"
+	eip55Addr = "0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed"
+	lowerAddr = "0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed"
+	upperAddr = "0X5AAEB6053F3E94C9B9A09F33669435E7EF1BEAED"
+	noPfxAddr = "5aaeb6053f3e94c9b9a09f33669435e7ef1beaed"
+	mixedHash = "0xB28F49668e7e76dc96D7aaBE5b7f63FEcfbd1c3574774c05e8204e749fd96fbd"
+	lowerHash = "0xb28f49668e7e76dc96d7aabe5b7f63fecfbd1c3574774c05e8204e749fd96fbd"
+	noPfxHash = "b28f49668e7e76dc96d7aabe5b7f63fecfbd1c3574774c05e8204e749fd96fbd"
+	solPubkey = "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v"
+	solSig    = "5j7s6NiJS3JAkvgkoc18WVAsiSaci2pxB2A6ueCJP4tprA2TFg9wSyTLeYouxPBJEMzJinENTkpA52YStRW5Dia7"
 )
 
 func TestCanonicalizeEVMAddress_EquivalentEncodingsConverge(t *testing.T) {
@@ -134,3 +139,72 @@ func TestCAIP2Namespace(t *testing.T) {
 	require.Equal(t, "solana", utils.CAIP2Namespace("solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1"))
 	require.Equal(t, "", utils.CAIP2Namespace("no-colon"))
 }
+
+// referenceSolanaTxHash reproduces the pre-fix behaviour for pure-base58 input:
+// decode unconditionally, convert only on an exact 64-byte result, otherwise
+// return the input untouched. The length band added in canonicalizeSolanaTxHash
+// must not change the result for any input.
+func referenceSolanaTxHash(s string) string {
+	if raw, err := base58.Decode(s); err == nil && len(raw) == 64 {
+		return "0x" + hex.EncodeToString(raw)
+	}
+	return s
+}
+
+func TestCanonicalizeTxHashByNamespace_Solana_LengthBandIsOutputEquivalent(t *testing.T) {
+	// Only 64..88 base58 chars can decode to exactly 64 bytes, so the band gate
+	// is a pure performance change. Sweep across it — 63/64/88/89 are the edges.
+	rng := rand.New(rand.NewSource(1))
+	alphabet := []byte("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz")
+
+	lengths := []int{1, 2, 31, 32, 43, 44, 63, 64, 65, 87, 88, 89, 90, 128, 200, 300}
+	for n := 3; n < 63; n += 7 {
+		lengths = append(lengths, n)
+	}
+
+	for _, n := range lengths {
+		for variant := 0; variant < 4; variant++ {
+			b := make([]byte, n)
+			for i := range b {
+				switch variant {
+				case 0:
+					b[i] = '1' // all-zero decode: the short edge of the band
+				case 1:
+					b[i] = 'z' // largest digit: the long edge
+				default:
+					b[i] = alphabet[rng.Intn(len(alphabet))]
+				}
+			}
+			in := string(b)
+			require.Equal(t, referenceSolanaTxHash(in),
+				utils.LenientCanonicalizeTxHash("solana:devnet", in),
+				"length band changed the result for a %d-char input %q", n, in)
+		}
+	}
+}
+
+func TestCanonicalizeTxHashByNamespace_Solana_RealSignatureStillConverges(t *testing.T) {
+	// The band must not break the case it exists to serve: an 88-char base58
+	// signature still folds to 0x-hex.
+	got, err := utils.CanonicalizeTxHashByNamespace("solana:devnet", solSig)
+	require.NoError(t, err)
+	require.Equal(t, "0x", got[:2])
+	require.Len(t, got, 2+128)
+}
+
+func TestCanonicalizeTxHashByNamespace_Solana_OversizedInputDoesNotDecode(t *testing.T) {
+	// F-2026-18821: mr-tron/base58 decoding is quadratic, and the result for an
+	// out-of-band length is discarded. Before the fix a single 1e5-char decode
+	// measured 4.5-29s (and InboundKeys does three of them); after, no decode
+	// runs at all. The bound is loose enough not to flake on a busy CI box while
+	// still failing hard on any return to O(n^2).
+	huge := strings.Repeat("z", 100_000)
+
+	start := time.Now()
+	got := utils.LenientCanonicalizeTxHash("solana:devnet", huge)
+	elapsed := time.Since(start)
+
+	require.Equal(t, huge, got, "out-of-band input must pass through unchanged")
+	require.Less(t, elapsed, time.Second,
+		"oversized base58 tx_hash must not be decoded (took %s)", elapsed)
+}

x/uexecutor/keeper/query_keys.go

@@ -12,13 +12,29 @@ import (
 	"github.com/pushchain/push-chain-node/x/uexecutor/types"
 )
 
+// maxQueryTxHashLen bounds the tx_hash accepted by the unauthenticated key
+// derivation queries. Longest real value is an 88-char base58 Solana signature.
+const maxQueryTxHashLen = 128
+
 // InboundKeys derives the canonical UTX id and inbound ballot id for the given
 // inbound, applying the same canonicalization the vote path uses. Lets off-chain
 // validators read the keys from the chain instead of re-implementing the rules.
 func (k Querier) InboundKeys(goCtx context.Context, req *types.QueryInboundKeysRequest) (*types.QueryInboundKeysResponse, error) {
 	if req == nil || req.Inbound == nil {
 		return nil, status.Error(codes.InvalidArgument, "inbound is required")
 	}
+	// This endpoint is unauthenticated, reads no state and so consumes no gas.
+	// Bound the one field that drives a decode (tx_hash) rather than trusting
+	// the caller. The limit is far above any real hash — 88 chars for a base58
+	// Solana signature, 66 for 0x-prefixed EVM — so it rejects only garbage.
+	// Deliberately not applied to raw_payload / verification_data, which are
+	// legitimately long, nor pushed down into utils.Canonicalize*: the vote
+	// path must stay lenient (a malformed inbound still has to produce a UTX),
+	// and changing shared canonicalization would alter ballot keys.
+	if n := len(req.Inbound.TxHash); n > maxQueryTxHashLen {
+		return nil, status.Errorf(codes.InvalidArgument,
+			"tx_hash too long: %d chars (max %d)", n, maxQueryTxHashLen)
+	}
 
 	inbound := *req.Inbound
 	inbound.Canonicalize()

x/uexecutor/keeper/query_keys_test.go

@@ -0,0 +1,87 @@
+package keeper_test
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
+	"github.com/pushchain/push-chain-node/x/uexecutor/types"
+)
+
+// solanaSig is a real 88-char base58 Solana signature (64 bytes).
+const solanaSig = "5j7s6NiJS3JAkvgkoc18WVAsiSaci2pxB2A6ueCJP4tprA2TFg9wSyTLeYouxPBJEMzJinENTkpA52YStRW5Dia7"
+
+func TestInboundKeys_RejectsOversizedTxHash(t *testing.T) {
+	// F-2026-18821: InboundKeys is unauthenticated, reads no state and so burns
+	// no gas. It canonicalizes tx_hash three times (Canonicalize, then the UTX
+	// and ballot key helpers), and base58 decoding is quadratic — a 1e5-char
+	// hash cost tens of seconds of CPU per request before the fix.
+	f := SetupTest(t)
+
+	huge := strings.Repeat("z", 100_000)
+
+	start := time.Now()
+	_, err := f.queryServer.InboundKeys(f.ctx, &types.QueryInboundKeysRequest{
+		Inbound: &types.Inbound{
+			SourceChain: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1",
+			TxHash:      huge,
+			LogIndex:    "0",
+			TxType:      types.TxType_FUNDS,
+		},
+	})
+	elapsed := time.Since(start)
+
+	require.Error(t, err)
+	require.Equal(t, codes.InvalidArgument, status.Code(err))
+	require.Contains(t, err.Error(), "tx_hash too long")
+	require.Less(t, elapsed, time.Second, "oversized tx_hash must fail fast (took %s)", elapsed)
+}
+
+func TestInboundKeys_AcceptsRealSolanaSignature(t *testing.T) {
+	// The cap must not reject anything real: 88 chars is the longest a base58
+	// 64-byte signature can be.
+	f := SetupTest(t)
+
+	resp, err := f.queryServer.InboundKeys(f.ctx, &types.QueryInboundKeysRequest{
+		Inbound: &types.Inbound{
+			SourceChain: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1",
+			TxHash:      solanaSig,
+			LogIndex:    "0",
+			TxType:      types.TxType_FUNDS,
+		},
+	})
+
+	require.NoError(t, err)
+	require.NotEmpty(t, resp.UtxId)
+	require.NotEmpty(t, resp.BallotId)
+	// Canonicalization folds the base58 signature into 0x-hex.
+	require.Equal(t, "0x", resp.CanonicalInbound.TxHash[:2])
+	require.Len(t, resp.CanonicalInbound.TxHash, 2+128)
+}
+
+func TestInboundKeys_TxHashAtCapIsAccepted(t *testing.T) {
+	// Boundary: exactly maxQueryTxHashLen (128) is allowed, 129 is not.
+	f := SetupTest(t)
+
+	newReq := func(n int) *types.QueryInboundKeysRequest {
+		return &types.QueryInboundKeysRequest{
+			Inbound: &types.Inbound{
+				SourceChain: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1",
+				TxHash:      strings.Repeat("z", n),
+				LogIndex:    "0",
+				TxType:      types.TxType_FUNDS,
+			},
+		}
+	}
+
+	_, err := f.queryServer.InboundKeys(f.ctx, newReq(128))
+	require.NoError(t, err, "128-char tx_hash is at the cap and must be accepted")
+
+	_, err = f.queryServer.InboundKeys(f.ctx, newReq(129))
+	require.Error(t, err)
+	require.Equal(t, codes.InvalidArgument, status.Code(err))
+}