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

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

src/script/interpreter.cpp

@@ -79,8 +79,20 @@ bool static IsCompressedOrUncompressedPubKey(const valtype &vchPubKey) {
             return false;
         }
     } else {
-          //  Non-canonical public key: neither compressed nor uncompressed
-          return false;
+        //  Non-canonical public key: neither compressed nor uncompressed
+        return false;
+    }
+    return true;
+}
+
+bool static IsCompressedPubKey(const valtype &vchPubKey) {
+    if (vchPubKey.size() != 33) {
+        //  Non-canonical public key: invalid length for compressed key
+        return false;
+    }
+    if (vchPubKey[0] != 0x02 && vchPubKey[0] != 0x03) {
+        //  Non-canonical public key: invalid prefix for compressed key
+        return false;
     }
     return true;
 }
@@ -199,10 +211,14 @@ bool CheckSignatureEncoding(const vector<unsigned char> &vchSig, unsigned int fl
     return true;
 }
 
-bool static CheckPubKeyEncoding(const valtype &vchSig, unsigned int flags, ScriptError* serror) {
-    if ((flags & SCRIPT_VERIFY_STRICTENC) != 0 && !IsCompressedOrUncompressedPubKey(vchSig)) {
+bool static CheckPubKeyEncoding(const valtype &vchPubKey, unsigned int flags, const SigVersion &sigversion, ScriptError* serror) {
+    if ((flags & SCRIPT_VERIFY_STRICTENC) != 0 && !IsCompressedOrUncompressedPubKey(vchPubKey)) {
         return set_error(serror, SCRIPT_ERR_PUBKEYTYPE);
     }
+    // Only compressed keys are accepted in segwit
+    if ((flags & SCRIPT_VERIFY_WITNESS_PUBKEYTYPE) != 0 && sigversion == SIGVERSION_WITNESS_V0 && !IsCompressedPubKey(vchPubKey)) {
+        return set_error(serror, SCRIPT_ERR_WITNESS_PUBKEYTYPE);
+    }
     return true;
 }
 
@@ -879,7 +895,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                         scriptCode.FindAndDelete(CScript(vchSig));
                     }
 
-                    if (!CheckSignatureEncoding(vchSig, flags, serror) || !CheckPubKeyEncoding(vchPubKey, flags, serror)) {
+                    if (!CheckSignatureEncoding(vchSig, flags, serror) || !CheckPubKeyEncoding(vchPubKey, flags, sigversion, serror)) {
                         //serror is set
                         return false;
                     }
@@ -953,7 +969,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                         // Note how this makes the exact order of pubkey/signature evaluation
                         // distinguishable by CHECKMULTISIG NOT if the STRICTENC flag is set.
                         // See the script_(in)valid tests for details.
-                        if (!CheckSignatureEncoding(vchSig, flags, serror) || !CheckPubKeyEncoding(vchPubKey, flags, serror)) {
+                        if (!CheckSignatureEncoding(vchSig, flags, serror) || !CheckPubKeyEncoding(vchPubKey, flags, sigversion, serror)) {
                             // serror is set
                             return false;
                         }

src/script/interpreter.h

@@ -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.
 
@@ -102,6 +102,10 @@ enum
     // Signature(s) must be empty vector if an CHECK(MULTI)SIG operation failed
     //
     SCRIPT_VERIFY_NULLFAIL = (1U << 14),
+
+    // Public keys in segregated witness scripts must be compressed
+    //
+    SCRIPT_VERIFY_WITNESS_PUBKEYTYPE = (1U << 15),
 };
 
 bool CheckSignatureEncoding(const std::vector<unsigned char> &vchSig, unsigned int flags, ScriptError* serror);

src/script/script_error.cpp

@@ -85,6 +85,8 @@ const char* ScriptErrorString(const ScriptError serror)
             return "Witness requires only-redeemscript scriptSig";
         case SCRIPT_ERR_WITNESS_UNEXPECTED:
             return "Witness provided for non-witness script";
+        case SCRIPT_ERR_WITNESS_PUBKEYTYPE:
+            return "Using non-compressed keys in segwit";
         case SCRIPT_ERR_UNKNOWN_ERROR:
         case SCRIPT_ERR_ERROR_COUNT:
         default: break;

src/script/script_error.h

@@ -62,6 +62,7 @@ typedef enum ScriptError_t
     SCRIPT_ERR_WITNESS_MALLEATED,
     SCRIPT_ERR_WITNESS_MALLEATED_P2SH,
     SCRIPT_ERR_WITNESS_UNEXPECTED,
+    SCRIPT_ERR_WITNESS_PUBKEYTYPE,
 
     SCRIPT_ERR_ERROR_COUNT
 } ScriptError;

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;