Add signature checking flag for when no sighash byte is expected

Author: instagibbs

src/pow.cpp

@@ -80,7 +80,8 @@ bool CheckProof(const CBlockHeader& block, const Consensus::Params& params)
         | SCRIPT_VERIFY_MINIMALDATA // Pushes are minimally-sized
         | SCRIPT_VERIFY_SIGPUSHONLY // Witness is push-only
         | SCRIPT_VERIFY_LOW_S // Stop easiest signature fiddling
-        | SCRIPT_VERIFY_WITNESS; // Required for cleanstack eval in VerifyScript
+        | SCRIPT_VERIFY_WITNESS // Required for cleanstack eval in VerifyScript
+        | SCRIPT_NO_SIGHASH_BYTE; // non-Check(Multi)Sig signatures will not have sighash byte
     return GenericVerifyScript(block.proof.solution, block.proof.challenge, proof_flags, block);
 }
 

src/script/interpreter.cpp

@@ -223,12 +223,19 @@ bool CheckSignatureEncoding(const vector<unsigned char> &vchSig, unsigned int fl
     if (vchSig.size() == 0) {
         return true;
     }
-    if ((flags & (SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_LOW_S | SCRIPT_VERIFY_STRICTENC)) != 0 && !IsValidSignatureEncoding(vchSig)) {
+    bool no_hash_byte = (flags & SCRIPT_NO_SIGHASH_BYTE) == SCRIPT_NO_SIGHASH_BYTE;
+    std::vector<unsigned char> vchSigCopy(vchSig.begin(), vchSig.begin() + vchSig.size());
+    // Push a dummy sighash byte to pass checks
+    if (no_hash_byte) {
+        vchSigCopy.push_back(SIGHASH_ALL);
+    }
+
+    if ((flags & (SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_LOW_S | SCRIPT_VERIFY_STRICTENC)) != 0 && !IsValidSignatureEncoding(vchSigCopy)) {
         return set_error(serror, SCRIPT_ERR_SIG_DER);
-    } else if ((flags & SCRIPT_VERIFY_LOW_S) != 0 && !IsLowDERSignature(vchSig, serror)) {
+    } else if ((flags & SCRIPT_VERIFY_LOW_S) != 0 && !IsLowDERSignature(vchSigCopy, serror)) {
         // serror is set
         return false;
-    } else if ((flags & SCRIPT_VERIFY_STRICTENC) != 0 && !IsDefinedHashtypeSignature(vchSig)) {
+    } else if ((flags & SCRIPT_VERIFY_STRICTENC) != 0 && !IsDefinedHashtypeSignature(vchSigCopy)) {
         return set_error(serror, SCRIPT_ERR_SIG_HASHTYPE);
     }
     return true;
@@ -1313,8 +1320,8 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     valtype& vchData   = stacktop(-2);
                     valtype& vchPubKey = stacktop(-1);
 
-                    // Sigs from stack have no hash type, so we disable strictenc check
-                    if (!CheckSignatureEncoding(vchSig, (flags & ~SCRIPT_VERIFY_STRICTENC), serror) || !CheckPubKeyEncoding(vchPubKey, flags, sigversion, serror)) {
+                    // Sigs from stack have no hash byte ever
+                    if (!CheckSignatureEncoding(vchSig, (flags | SCRIPT_NO_SIGHASH_BYTE), serror) || !CheckPubKeyEncoding(vchPubKey, flags, sigversion, serror)) {
                         //serror is set
                         return false;
                     }

src/script/interpreter.h

@@ -107,6 +107,10 @@ enum
     // Public keys in segregated witness scripts must be compressed
     //
     SCRIPT_VERIFY_WITNESS_PUBKEYTYPE = (1U << 15),
+
+    // Signature checking assumes no sighash byte after the DER signature
+    //
+    SCRIPT_NO_SIGHASH_BYTE = (1U << 16),
 
 };