Add fake pubkey filter

backend/src/api/common.ts

@@ -6,6 +6,7 @@ import { NodeSocket } from '../repositories/NodesSocketsRepository';
 import { isIP } from 'net';
 import rbfCache from './rbf-cache';
 import transactionUtils from './transaction-utils';
+import { isPoint } from '../utils/secp256k1';
 export class Common {
   static nativeAssetId = config.MEMPOOL.NETWORK === 'liquidtestnet' ?
     '144c654344aa716d6f3abcc1ca90e5641e4e2a7f633bc09fe3baf64585819a49'
@@ -211,6 +212,15 @@ export class Common {
     }
   }
 
+  static isBurnKey(pubkey: string): boolean {
+    return [
+      '022222222222222222222222222222222222222222222222222222222222222222',
+      '033333333333333333333333333333333333333333333333333333333333333333',
+      '020202020202020202020202020202020202020202020202020202020202020202',
+      '030303030303030303030303030303030303030303030303030303030303030303',
+    ].includes(pubkey);
+  }
+
   static getTransactionFlags(tx: TransactionExtended): number {
     let flags = 0n;
     if (tx.version === 1) {
@@ -249,8 +259,8 @@ export class Common {
         flags |= this.setSchnorrSighashFlags(flags, vin.witness);
       } else if (vin.witness) {
         flags |= this.setSegwitSighashFlags(flags, vin.witness);
-      } else if (vin.scriptsig_asm) {
-        flags |= this.setLegacySighashFlags(flags, vin.scriptsig_asm);
+      } else if (vin.scriptsig?.length) {
+        flags |= this.setLegacySighashFlags(flags, vin.scriptsig_asm || transactionUtils.convertScriptSigAsm(vin.scriptsig));
       }
 
       if (vin.prevout?.scriptpubkey_address) {
@@ -263,12 +273,23 @@ export class Common {
     } else {
       flags |= TransactionFlags.no_rbf;
     }
+    let hasFakePubkey = false;
     for (const vout of tx.vout) {
       switch (vout.scriptpubkey_type) {
-        case 'p2pk': flags |= TransactionFlags.p2pk; break;
+        case 'p2pk': {
+          flags |= TransactionFlags.p2pk;
+          // detect fake pubkey (i.e. not a valid DER point on the secp256k1 curve)
+          hasFakePubkey = hasFakePubkey || !isPoint(vout.scriptpubkey.slice(2, -2));
+        } break;
         case 'multisig': {
           flags |= TransactionFlags.p2ms;
-          // TODO - detect fake multisig data embedding
+          // detect fake pubkeys (i.e. not valid DER points on the secp256k1 curve)
+          const asm = vout.scriptpubkey_asm || transactionUtils.convertScriptSigAsm(vout.scriptpubkey);
+          for (const key of (asm?.split(' ') || [])) {
+            if (!hasFakePubkey && !key.startsWith('OP_')) {
+              hasFakePubkey = hasFakePubkey || this.isBurnKey(key) || !isPoint(key);
+            }
+          }
         } break;
         case 'p2pkh': flags |= TransactionFlags.p2pkh; break;
         case 'p2sh': flags |= TransactionFlags.p2sh; break;
@@ -282,6 +303,9 @@ export class Common {
       }
       outValues[vout.value || Math.random()] = (outValues[vout.value || Math.random()] || 0) + 1;
     }
+    if (hasFakePubkey) {
+      flags |= TransactionFlags.fake_pubkey;
+    }
     if (tx.ancestors?.length) {
       flags |= TransactionFlags.cpfp_child;
     }

backend/src/mempool.interfaces.ts

@@ -215,7 +215,7 @@ export const TransactionFlags = {
   replacement:                               0b00000100_00000000_00000000n,
   // data
   op_return:                        0b00000001_00000000_00000000_00000000n,
-  fake_multisig:                    0b00000010_00000000_00000000_00000000n,
+  fake_pubkey:                      0b00000010_00000000_00000000_00000000n,
   inscription:                      0b00000100_00000000_00000000_00000000n,
   // heuristics
   coinjoin:                0b00000001_00000000_00000000_00000000_00000000n,

backend/src/utils/secp256k1.ts

@@ -0,0 +1,74 @@
+function powMod(x: bigint, power: number, modulo: bigint): bigint {
+  for (let i = 0; i < power; i++) {
+    x = (x * x) % modulo;
+  }
+  return x;
+}
+
+function sqrtMod(x: bigint, P: bigint): bigint {
+  const b2 = (x * x * x) % P;
+  const b3 = (b2 * b2 * x) % P;
+  const b6 = (powMod(b3, 3, P) * b3) % P;
+  const b9 = (powMod(b6, 3, P) * b3) % P;
+  const b11 = (powMod(b9, 2, P) * b2) % P;
+  const b22 = (powMod(b11, 11, P) * b11) % P;
+  const b44 = (powMod(b22, 22, P) * b22) % P;
+  const b88 = (powMod(b44, 44, P) * b44) % P;
+  const b176 = (powMod(b88, 88, P) * b88) % P;
+  const b220 = (powMod(b176, 44, P) * b44) % P;
+  const b223 = (powMod(b220, 3, P) * b3) % P;
+  const t1 = (powMod(b223, 23, P) * b22) % P;
+  const t2 = (powMod(t1, 6, P) * b2) % P;
+  const root = powMod(t2, 2, P);
+  return root;
+}
+
+const curveP = BigInt(`0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F`);
+
+/**
+ * This function tells whether the point given is a DER encoded point on the ECDSA curve.
+ * @param {string} pointHex The point as a hex string (*must not* include a '0x' prefix)
+ * @returns {boolean} true if the point is on the SECP256K1 curve
+ */
+export function isPoint(pointHex: string): boolean {
+  if (
+    !(
+      // is uncompressed
+      (
+        (pointHex.length === 130 && pointHex.startsWith('04')) ||
+        // OR is compressed
+        (pointHex.length === 66 &&
+          (pointHex.startsWith('02') || pointHex.startsWith('03')))
+      )
+    )
+  ) {
+    return false;
+  }
+
+  // Function modified slightly from noble-curves
+  
+
+  // Now we know that pointHex is a 33 or 65 byte hex string.
+  const isCompressed = pointHex.length === 66;
+
+  const x = BigInt(`0x${pointHex.slice(2, 66)}`);
+  if (x >= curveP) {
+    return false;
+  }
+
+  if (!isCompressed) {
+    const y = BigInt(`0x${pointHex.slice(66, 130)}`);
+    if (y >= curveP) {
+      return false;
+    }
+    // Just check y^2 = x^3 + 7 (secp256k1 curve)
+    return (y * y) % curveP === (x * x * x + 7n) % curveP;
+  } else {
+    // Get unaltered y^2 (no mod p)
+    const ySquared = (x * x * x + 7n) % curveP;
+    // Try to sqrt it, it will round down if not perfect root
+    const y = sqrtMod(ySquared, curveP);
+    // If we square and it's equal, then it was a perfect root and valid point.
+    return (y * y) % curveP === ySquared;
+  }
+}