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src/script/interpreter.cpp

@@ -174,7 +174,13 @@ bool static IsLowDERSignature(const valtype &vchSig, ScriptError* serror) {
     if (!IsValidSignatureEncoding(vchSig)) {
         return set_error(serror, SCRIPT_ERR_SIG_DER);
     }
+    // https://bitcoin.stackexchange.com/a/12556:
+    //     Also note that inside transaction signatures, an extra hashtype byte
+    //     follows the actual signature data.
     std::vector<unsigned char> vchSigCopy(vchSig.begin(), vchSig.begin() + vchSig.size() - 1);
+    // If the S value is above the order of the curve divided by two, its
+    // complement modulo the order could have been used instead, which is
+    // one byte shorter when encoded correctly.
     if (!CPubKey::CheckLowS(vchSigCopy)) {
         return set_error(serror, SCRIPT_ERR_SIG_HIGH_S);
     }