Require compressed keys in segwit as policy and disable signing with uncompressed keys for segwit scripts

Github-Pull: #8499
Rebased-From: 4c0c25a604cec39675187507df423cff5d707ab5

src/script/sign.cpp

@@ -1,5 +1,5 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2015 The Bitcoin Core developers
+// Copyright (c) 2009-2016 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -26,6 +26,10 @@ bool TransactionSignatureCreator::CreateSig(std::vector<unsigned char>& vchSig,
     if (!keystore->GetKey(address, key))
         return false;
 
+    // Signing with uncompressed keys is disabled in witness scripts
+    if (sigversion == SIGVERSION_WITNESS_V0 && !key.IsCompressed())
+        return false;
+
     uint256 hash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion);
     if (!key.Sign(hash, vchSig))
         return false;