Validate signatures from both 0.8.7 and 0.10.4

src/script/interpreter.cpp

@@ -1057,13 +1057,15 @@ private:
     const bool fAnyoneCanPay;  //!< whether the hashtype has the SIGHASH_ANYONECANPAY flag set
     const bool fHashSingle;    //!< whether the hashtype is SIGHASH_SINGLE
     const bool fHashNone;      //!< whether the hashtype is SIGHASH_NONE
+    const bool fOmitTxComment; //!< whether the hashtype has the SIGHASH_OMIT_TX_COMMENT flag set
 
 public:
     CTransactionSignatureSerializer(const CTransaction &txToIn, const CScript &scriptCodeIn, unsigned int nInIn, int nHashTypeIn) :
         txTo(txToIn), scriptCode(scriptCodeIn), nIn(nInIn),
         fAnyoneCanPay(!!(nHashTypeIn & SIGHASH_ANYONECANPAY)),
         fHashSingle((nHashTypeIn & 0x1f) == SIGHASH_SINGLE),
-        fHashNone((nHashTypeIn & 0x1f) == SIGHASH_NONE) {}
+        fHashNone((nHashTypeIn & 0x1f) == SIGHASH_NONE),
+        fOmitTxComment(!!(nHashTypeIn & SIGHASH_OMIT_TX_COMMENT)){}
 
     /** Serialize the passed scriptCode, skipping OP_CODESEPARATORs */
     template<typename S>
@@ -1138,7 +1140,7 @@ public:
         // Serialize nLockTime
         ::Serialize(s, txTo.nLockTime);
         // Serialize strTxComment
-        if (txTo.nVersion >= 2)
+        if (txTo.nVersion >= 2 && fOmitTxComment == 0)
         	 ::Serialize(s, txTo.strTxComment);
     }
 };
@@ -1246,6 +1248,9 @@ uint256 SignatureHash(const CScript& scriptCode, const CTransaction& txTo, unsig
 
     // Serialize and hash
     CHashWriter ss(SER_GETHASH, 0);
+    nHashType &= ~SIGHASH_OMIT_TX_COMMENT; // clear SIGHASH_OMIT_TX_COMMENT - Flag is only used for 0.10.4 compat
+                                           // it's used internally but must not actually appear in the result
+
     ss << txTmp << nHashType;
     return ss.GetHash();
 }
@@ -1270,8 +1275,20 @@ bool TransactionSignatureChecker::CheckSig(const std::vector<unsigned char>& vch
 
     uint256 sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion, this->txdata);
 
-    if (!VerifySignature(vchSig, pubkey, sighash))
-        return false;
+    if (!VerifySignature(vchSig, pubkey, sighash)){
+        // Verification failed, toggle SIGHASH_OMIT_TX_COMMENT and try again
+        nHashType ^= SIGHASH_OMIT_TX_COMMENT;
+
+        // need a new vchSig
+        std::vector<unsigned char> vchSig2(vchSigIn);
+        // pop the hash type
+        vchSig2.pop_back();
+
+        sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion, this->txdata);
+
+        if (!VerifySignature(vchSig2, pubkey, sighash))
+            return false;
+    }
 
     return true;
 }

src/script/interpreter.h

@@ -25,6 +25,7 @@ enum
     SIGHASH_NONE = 2,
     SIGHASH_SINGLE = 3,
     SIGHASH_ANYONECANPAY = 0x80,
+    SIGHASH_OMIT_TX_COMMENT = (1U << 6),
 };
 
 /** Script verification flags */