Separate script/interpreter

2 files changed, 1093 insertions, 0 deletions

diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
new file mode 100644
index 0000000000..4f4fdb6b7f
--- /dev/null
+++ b/src/script/interpreter.cpp
@@ -0,0 +1,1048 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2013 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "interpreter.h"
+
+#include "core.h"
+#include "crypto/ripemd160.h"
+#include "crypto/sha1.h"
+#include "crypto/sha2.h"
+#include "random.h"
+#include "script/script.h"
+#include "uint256.h"
+#include "util.h"
+
+#include <boost/thread.hpp>
+#include <boost/tuple/tuple_comparison.hpp>
+
+using namespace std;
+
+typedef vector<unsigned char> valtype;
+static const valtype vchFalse(0);
+static const valtype vchZero(0);
+static const valtype vchTrue(1, 1);
+static const CScriptNum bnZero(0);
+static const CScriptNum bnOne(1);
+static const CScriptNum bnFalse(0);
+static const CScriptNum bnTrue(1);
+
+bool CastToBool(const valtype& vch)
+{
+    for (unsigned int i = 0; i < vch.size(); i++)
+    {
+        if (vch[i] != 0)
+        {
+            // Can be negative zero
+            if (i == vch.size()-1 && vch[i] == 0x80)
+                return false;
+            return true;
+        }
+    }
+    return false;
+}
+
+//
+// Script is a stack machine (like Forth) that evaluates a predicate
+// returning a bool indicating valid or not.  There are no loops.
+//
+#define stacktop(i)  (stack.at(stack.size()+(i)))
+#define altstacktop(i)  (altstack.at(altstack.size()+(i)))
+static inline void popstack(vector<valtype>& stack)
+{
+    if (stack.empty())
+        throw runtime_error("popstack() : stack empty");
+    stack.pop_back();
+}
+
+bool IsCanonicalPubKey(const valtype &vchPubKey, unsigned int flags) {
+    if (!(flags & SCRIPT_VERIFY_STRICTENC))
+        return true;
+
+    if (vchPubKey.size() < 33)
+        return error("Non-canonical public key: too short");
+    if (vchPubKey[0] == 0x04) {
+        if (vchPubKey.size() != 65)
+            return error("Non-canonical public key: invalid length for uncompressed key");
+    } else if (vchPubKey[0] == 0x02 || vchPubKey[0] == 0x03) {
+        if (vchPubKey.size() != 33)
+            return error("Non-canonical public key: invalid length for compressed key");
+    } else {
+        return error("Non-canonical public key: neither compressed nor uncompressed");
+    }
+    return true;
+}
+
+bool IsCanonicalSignature(const valtype &vchSig, unsigned int flags) {
+    if (!(flags & SCRIPT_VERIFY_STRICTENC))
+        return true;
+
+    // See https://bitcointalk.org/index.php?topic=8392.msg127623#msg127623
+    // A canonical signature exists of: <30> <total len> <02> <len R> <R> <02> <len S> <S> <hashtype>
+    // Where R and S are not negative (their first byte has its highest bit not set), and not
+    // excessively padded (do not start with a 0 byte, unless an otherwise negative number follows,
+    // in which case a single 0 byte is necessary and even required).
+    if (vchSig.size() < 9)
+        return error("Non-canonical signature: too short");
+    if (vchSig.size() > 73)
+        return error("Non-canonical signature: too long");
+    unsigned char nHashType = vchSig[vchSig.size() - 1] & (~(SIGHASH_ANYONECANPAY));
+    if (nHashType < SIGHASH_ALL || nHashType > SIGHASH_SINGLE)
+        return error("Non-canonical signature: unknown hashtype byte");
+    if (vchSig[0] != 0x30)
+        return error("Non-canonical signature: wrong type");
+    if (vchSig[1] != vchSig.size()-3)
+        return error("Non-canonical signature: wrong length marker");
+    unsigned int nLenR = vchSig[3];
+    if (5 + nLenR >= vchSig.size())
+        return error("Non-canonical signature: S length misplaced");
+    unsigned int nLenS = vchSig[5+nLenR];
+    if ((unsigned long)(nLenR+nLenS+7) != vchSig.size())
+        return error("Non-canonical signature: R+S length mismatch");
+
+    const unsigned char *R = &vchSig[4];
+    if (R[-2] != 0x02)
+        return error("Non-canonical signature: R value type mismatch");
+    if (nLenR == 0)
+        return error("Non-canonical signature: R length is zero");
+    if (R[0] & 0x80)
+        return error("Non-canonical signature: R value negative");
+    if (nLenR > 1 && (R[0] == 0x00) && !(R[1] & 0x80))
+        return error("Non-canonical signature: R value excessively padded");
+
+    const unsigned char *S = &vchSig[6+nLenR];
+    if (S[-2] != 0x02)
+        return error("Non-canonical signature: S value type mismatch");
+    if (nLenS == 0)
+        return error("Non-canonical signature: S length is zero");
+    if (S[0] & 0x80)
+        return error("Non-canonical signature: S value negative");
+    if (nLenS > 1 && (S[0] == 0x00) && !(S[1] & 0x80))
+        return error("Non-canonical signature: S value excessively padded");
+
+    if (flags & SCRIPT_VERIFY_LOW_S) {
+        // 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 (!CKey::CheckSignatureElement(S, nLenS, true))
+            return error("Non-canonical signature: S value is unnecessarily high");
+    }
+
+    return true;
+}
+
+bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, const CTransaction& txTo, unsigned int nIn, unsigned int flags, int nHashType)
+{
+    CScript::const_iterator pc = script.begin();
+    CScript::const_iterator pend = script.end();
+    CScript::const_iterator pbegincodehash = script.begin();
+    opcodetype opcode;
+    valtype vchPushValue;
+    vector<bool> vfExec;
+    vector<valtype> altstack;
+    if (script.size() > 10000)
+        return false;
+    int nOpCount = 0;
+
+    try
+    {
+        while (pc < pend)
+        {
+            bool fExec = !count(vfExec.begin(), vfExec.end(), false);
+
+            //
+            // Read instruction
+            //
+            if (!script.GetOp(pc, opcode, vchPushValue))
+                return false;
+            if (vchPushValue.size() > MAX_SCRIPT_ELEMENT_SIZE)
+                return false;
+
+            // Note how OP_RESERVED does not count towards the opcode limit.
+            if (opcode > OP_16 && ++nOpCount > 201)
+                return false;
+
+            if (opcode == OP_CAT ||
+                opcode == OP_SUBSTR ||
+                opcode == OP_LEFT ||
+                opcode == OP_RIGHT ||
+                opcode == OP_INVERT ||
+                opcode == OP_AND ||
+                opcode == OP_OR ||
+                opcode == OP_XOR ||
+                opcode == OP_2MUL ||
+                opcode == OP_2DIV ||
+                opcode == OP_MUL ||
+                opcode == OP_DIV ||
+                opcode == OP_MOD ||
+                opcode == OP_LSHIFT ||
+                opcode == OP_RSHIFT)
+                return false; // Disabled opcodes.
+
+            if (fExec && 0 <= opcode && opcode <= OP_PUSHDATA4)
+                stack.push_back(vchPushValue);
+            else if (fExec || (OP_IF <= opcode && opcode <= OP_ENDIF))
+            switch (opcode)
+            {
+                //
+                // Push value
+                //
+                case OP_1NEGATE:
+                case OP_1:
+                case OP_2:
+                case OP_3:
+                case OP_4:
+                case OP_5:
+                case OP_6:
+                case OP_7:
+                case OP_8:
+                case OP_9:
+                case OP_10:
+                case OP_11:
+                case OP_12:
+                case OP_13:
+                case OP_14:
+                case OP_15:
+                case OP_16:
+                {
+                    // ( -- value)
+                    CScriptNum bn((int)opcode - (int)(OP_1 - 1));
+                    stack.push_back(bn.getvch());
+                }
+                break;
+
+
+                //
+                // Control
+                //
+                case OP_NOP:
+                case OP_NOP1: case OP_NOP2: case OP_NOP3: case OP_NOP4: case OP_NOP5:
+                case OP_NOP6: case OP_NOP7: case OP_NOP8: case OP_NOP9: case OP_NOP10:
+                break;
+
+                case OP_IF:
+                case OP_NOTIF:
+                {
+                    // <expression> if [statements] [else [statements]] endif
+                    bool fValue = false;
+                    if (fExec)
+                    {
+                        if (stack.size() < 1)
+                            return false;
+                        valtype& vch = stacktop(-1);
+                        fValue = CastToBool(vch);
+                        if (opcode == OP_NOTIF)
+                            fValue = !fValue;
+                        popstack(stack);
+                    }
+                    vfExec.push_back(fValue);
+                }
+                break;
+
+                case OP_ELSE:
+                {
+                    if (vfExec.empty())
+                        return false;
+                    vfExec.back() = !vfExec.back();
+                }
+                break;
+
+                case OP_ENDIF:
+                {
+                    if (vfExec.empty())
+                        return false;
+                    vfExec.pop_back();
+                }
+                break;
+
+                case OP_VERIFY:
+                {
+                    // (true -- ) or
+                    // (false -- false) and return
+                    if (stack.size() < 1)
+                        return false;
+                    bool fValue = CastToBool(stacktop(-1));
+                    if (fValue)
+                        popstack(stack);
+                    else
+                        return false;
+                }
+                break;
+
+                case OP_RETURN:
+                {
+                    return false;
+                }
+                break;
+
+
+                //
+                // Stack ops
+                //
+                case OP_TOALTSTACK:
+                {
+                    if (stack.size() < 1)
+                        return false;
+                    altstack.push_back(stacktop(-1));
+                    popstack(stack);
+                }
+                break;
+
+                case OP_FROMALTSTACK:
+                {
+                    if (altstack.size() < 1)
+                        return false;
+                    stack.push_back(altstacktop(-1));
+                    popstack(altstack);
+                }
+                break;
+
+                case OP_2DROP:
+                {
+                    // (x1 x2 -- )
+                    if (stack.size() < 2)
+                        return false;
+                    popstack(stack);
+                    popstack(stack);
+                }
+                break;
+
+                case OP_2DUP:
+                {
+                    // (x1 x2 -- x1 x2 x1 x2)
+                    if (stack.size() < 2)
+                        return false;
+                    valtype vch1 = stacktop(-2);
+                    valtype vch2 = stacktop(-1);
+                    stack.push_back(vch1);
+                    stack.push_back(vch2);
+                }
+                break;
+
+                case OP_3DUP:
+                {
+                    // (x1 x2 x3 -- x1 x2 x3 x1 x2 x3)
+                    if (stack.size() < 3)
+                        return false;
+                    valtype vch1 = stacktop(-3);
+                    valtype vch2 = stacktop(-2);
+                    valtype vch3 = stacktop(-1);
+                    stack.push_back(vch1);
+                    stack.push_back(vch2);
+                    stack.push_back(vch3);
+                }
+                break;
+
+                case OP_2OVER:
+                {
+                    // (x1 x2 x3 x4 -- x1 x2 x3 x4 x1 x2)
+                    if (stack.size() < 4)
+                        return false;
+                    valtype vch1 = stacktop(-4);
+                    valtype vch2 = stacktop(-3);
+                    stack.push_back(vch1);
+                    stack.push_back(vch2);
+                }
+                break;
+
+                case OP_2ROT:
+                {
+                    // (x1 x2 x3 x4 x5 x6 -- x3 x4 x5 x6 x1 x2)
+                    if (stack.size() < 6)
+                        return false;
+                    valtype vch1 = stacktop(-6);
+                    valtype vch2 = stacktop(-5);
+                    stack.erase(stack.end()-6, stack.end()-4);
+                    stack.push_back(vch1);
+                    stack.push_back(vch2);
+                }
+                break;
+
+                case OP_2SWAP:
+                {
+                    // (x1 x2 x3 x4 -- x3 x4 x1 x2)
+                    if (stack.size() < 4)
+                        return false;
+                    swap(stacktop(-4), stacktop(-2));
+                    swap(stacktop(-3), stacktop(-1));
+                }
+                break;
+
+                case OP_IFDUP:
+                {
+                    // (x - 0 | x x)
+                    if (stack.size() < 1)
+                        return false;
+                    valtype vch = stacktop(-1);
+                    if (CastToBool(vch))
+                        stack.push_back(vch);
+                }
+                break;
+
+                case OP_DEPTH:
+                {
+                    // -- stacksize
+                    CScriptNum bn(stack.size());
+                    stack.push_back(bn.getvch());
+                }
+                break;
+
+                case OP_DROP:
+                {
+                    // (x -- )
+                    if (stack.size() < 1)
+                        return false;
+                    popstack(stack);
+                }
+                break;
+
+                case OP_DUP:
+                {
+                    // (x -- x x)
+                    if (stack.size() < 1)
+                        return false;
+                    valtype vch = stacktop(-1);
+                    stack.push_back(vch);
+                }
+                break;
+
+                case OP_NIP:
+                {
+                    // (x1 x2 -- x2)
+                    if (stack.size() < 2)
+                        return false;
+                    stack.erase(stack.end() - 2);
+                }
+                break;
+
+                case OP_OVER:
+                {
+                    // (x1 x2 -- x1 x2 x1)
+                    if (stack.size() < 2)
+                        return false;
+                    valtype vch = stacktop(-2);
+                    stack.push_back(vch);
+                }
+                break;
+
+                case OP_PICK:
+                case OP_ROLL:
+                {
+                    // (xn ... x2 x1 x0 n - xn ... x2 x1 x0 xn)
+                    // (xn ... x2 x1 x0 n - ... x2 x1 x0 xn)
+                    if (stack.size() < 2)
+                        return false;
+                    int n = CScriptNum(stacktop(-1)).getint();
+                    popstack(stack);
+                    if (n < 0 || n >= (int)stack.size())
+                        return false;
+                    valtype vch = stacktop(-n-1);
+                    if (opcode == OP_ROLL)
+                        stack.erase(stack.end()-n-1);
+                    stack.push_back(vch);
+                }
+                break;
+
+                case OP_ROT:
+                {
+                    // (x1 x2 x3 -- x2 x3 x1)
+                    //  x2 x1 x3  after first swap
+                    //  x2 x3 x1  after second swap
+                    if (stack.size() < 3)
+                        return false;
+                    swap(stacktop(-3), stacktop(-2));
+                    swap(stacktop(-2), stacktop(-1));
+                }
+                break;
+
+                case OP_SWAP:
+                {
+                    // (x1 x2 -- x2 x1)
+                    if (stack.size() < 2)
+                        return false;
+                    swap(stacktop(-2), stacktop(-1));
+                }
+                break;
+
+                case OP_TUCK:
+                {
+                    // (x1 x2 -- x2 x1 x2)
+                    if (stack.size() < 2)
+                        return false;
+                    valtype vch = stacktop(-1);
+                    stack.insert(stack.end()-2, vch);
+                }
+                break;
+
+
+                case OP_SIZE:
+                {
+                    // (in -- in size)
+                    if (stack.size() < 1)
+                        return false;
+                    CScriptNum bn(stacktop(-1).size());
+                    stack.push_back(bn.getvch());
+                }
+                break;
+
+
+                //
+                // Bitwise logic
+                //
+                case OP_EQUAL:
+                case OP_EQUALVERIFY:
+                //case OP_NOTEQUAL: // use OP_NUMNOTEQUAL
+                {
+                    // (x1 x2 - bool)
+                    if (stack.size() < 2)
+                        return false;
+                    valtype& vch1 = stacktop(-2);
+                    valtype& vch2 = stacktop(-1);
+                    bool fEqual = (vch1 == vch2);
+                    // OP_NOTEQUAL is disabled because it would be too easy to say
+                    // something like n != 1 and have some wiseguy pass in 1 with extra
+                    // zero bytes after it (numerically, 0x01 == 0x0001 == 0x000001)
+                    //if (opcode == OP_NOTEQUAL)
+                    //    fEqual = !fEqual;
+                    popstack(stack);
+                    popstack(stack);
+                    stack.push_back(fEqual ? vchTrue : vchFalse);
+                    if (opcode == OP_EQUALVERIFY)
+                    {
+                        if (fEqual)
+                            popstack(stack);
+                        else
+                            return false;
+                    }
+                }
+                break;
+
+
+                //
+                // Numeric
+                //
+                case OP_1ADD:
+                case OP_1SUB:
+                case OP_NEGATE:
+                case OP_ABS:
+                case OP_NOT:
+                case OP_0NOTEQUAL:
+                {
+                    // (in -- out)
+                    if (stack.size() < 1)
+                        return false;
+                    CScriptNum bn(stacktop(-1));
+                    switch (opcode)
+                    {
+                    case OP_1ADD:       bn += bnOne; break;
+                    case OP_1SUB:       bn -= bnOne; break;
+                    case OP_NEGATE:     bn = -bn; break;
+                    case OP_ABS:        if (bn < bnZero) bn = -bn; break;
+                    case OP_NOT:        bn = (bn == bnZero); break;
+                    case OP_0NOTEQUAL:  bn = (bn != bnZero); break;
+                    default:            assert(!"invalid opcode"); break;
+                    }
+                    popstack(stack);
+                    stack.push_back(bn.getvch());
+                }
+                break;
+
+                case OP_ADD:
+                case OP_SUB:
+                case OP_BOOLAND:
+                case OP_BOOLOR:
+                case OP_NUMEQUAL:
+                case OP_NUMEQUALVERIFY:
+                case OP_NUMNOTEQUAL:
+                case OP_LESSTHAN:
+                case OP_GREATERTHAN:
+                case OP_LESSTHANOREQUAL:
+                case OP_GREATERTHANOREQUAL:
+                case OP_MIN:
+                case OP_MAX:
+                {
+                    // (x1 x2 -- out)
+                    if (stack.size() < 2)
+                        return false;
+                    CScriptNum bn1(stacktop(-2));
+                    CScriptNum bn2(stacktop(-1));
+                    CScriptNum bn(0);
+                    switch (opcode)
+                    {
+                    case OP_ADD:
+                        bn = bn1 + bn2;
+                        break;
+
+                    case OP_SUB:
+                        bn = bn1 - bn2;
+                        break;
+
+                    case OP_BOOLAND:             bn = (bn1 != bnZero && bn2 != bnZero); break;
+                    case OP_BOOLOR:              bn = (bn1 != bnZero || bn2 != bnZero); break;
+                    case OP_NUMEQUAL:            bn = (bn1 == bn2); break;
+                    case OP_NUMEQUALVERIFY:      bn = (bn1 == bn2); break;
+                    case OP_NUMNOTEQUAL:         bn = (bn1 != bn2); break;
+                    case OP_LESSTHAN:            bn = (bn1 < bn2); break;
+                    case OP_GREATERTHAN:         bn = (bn1 > bn2); break;
+                    case OP_LESSTHANOREQUAL:     bn = (bn1 <= bn2); break;
+                    case OP_GREATERTHANOREQUAL:  bn = (bn1 >= bn2); break;
+                    case OP_MIN:                 bn = (bn1 < bn2 ? bn1 : bn2); break;
+                    case OP_MAX:                 bn = (bn1 > bn2 ? bn1 : bn2); break;
+                    default:                     assert(!"invalid opcode"); break;
+                    }
+                    popstack(stack);
+                    popstack(stack);
+                    stack.push_back(bn.getvch());
+
+                    if (opcode == OP_NUMEQUALVERIFY)
+                    {
+                        if (CastToBool(stacktop(-1)))
+                            popstack(stack);
+                        else
+                            return false;
+                    }
+                }
+                break;
+
+                case OP_WITHIN:
+                {
+                    // (x min max -- out)
+                    if (stack.size() < 3)
+                        return false;
+                    CScriptNum bn1(stacktop(-3));
+                    CScriptNum bn2(stacktop(-2));
+                    CScriptNum bn3(stacktop(-1));
+                    bool fValue = (bn2 <= bn1 && bn1 < bn3);
+                    popstack(stack);
+                    popstack(stack);
+                    popstack(stack);
+                    stack.push_back(fValue ? vchTrue : vchFalse);
+                }
+                break;
+
+
+                //
+                // Crypto
+                //
+                case OP_RIPEMD160:
+                case OP_SHA1:
+                case OP_SHA256:
+                case OP_HASH160:
+                case OP_HASH256:
+                {
+                    // (in -- hash)
+                    if (stack.size() < 1)
+                        return false;
+                    valtype& vch = stacktop(-1);
+                    valtype vchHash((opcode == OP_RIPEMD160 || opcode == OP_SHA1 || opcode == OP_HASH160) ? 20 : 32);
+                    if (opcode == OP_RIPEMD160)
+                        CRIPEMD160().Write(&vch[0], vch.size()).Finalize(&vchHash[0]);
+                    else if (opcode == OP_SHA1)
+                        CSHA1().Write(&vch[0], vch.size()).Finalize(&vchHash[0]);
+                    else if (opcode == OP_SHA256)
+                        CSHA256().Write(&vch[0], vch.size()).Finalize(&vchHash[0]);
+                    else if (opcode == OP_HASH160)
+                        CHash160().Write(&vch[0], vch.size()).Finalize(&vchHash[0]);
+                    else if (opcode == OP_HASH256)
+                        CHash256().Write(&vch[0], vch.size()).Finalize(&vchHash[0]);
+                    popstack(stack);
+                    stack.push_back(vchHash);
+                }
+                break;
+
+                case OP_CODESEPARATOR:
+                {
+                    // Hash starts after the code separator
+                    pbegincodehash = pc;
+                }
+                break;
+
+                case OP_CHECKSIG:
+                case OP_CHECKSIGVERIFY:
+                {
+                    // (sig pubkey -- bool)
+                    if (stack.size() < 2)
+                        return false;
+
+                    valtype& vchSig    = stacktop(-2);
+                    valtype& vchPubKey = stacktop(-1);
+
+                    // Subset of script starting at the most recent codeseparator
+                    CScript scriptCode(pbegincodehash, pend);
+
+                    // Drop the signature, since there's no way for a signature to sign itself
+                    scriptCode.FindAndDelete(CScript(vchSig));
+
+                    bool fSuccess = IsCanonicalSignature(vchSig, flags) && IsCanonicalPubKey(vchPubKey, flags) &&
+                        CheckSig(vchSig, vchPubKey, scriptCode, txTo, nIn, nHashType, flags);
+
+                    popstack(stack);
+                    popstack(stack);
+                    stack.push_back(fSuccess ? vchTrue : vchFalse);
+                    if (opcode == OP_CHECKSIGVERIFY)
+                    {
+                        if (fSuccess)
+                            popstack(stack);
+                        else
+                            return false;
+                    }
+                }
+                break;
+
+                case OP_CHECKMULTISIG:
+                case OP_CHECKMULTISIGVERIFY:
+                {
+                    // ([sig ...] num_of_signatures [pubkey ...] num_of_pubkeys -- bool)
+
+                    int i = 1;
+                    if ((int)stack.size() < i)
+                        return false;
+
+                    int nKeysCount = CScriptNum(stacktop(-i)).getint();
+                    if (nKeysCount < 0 || nKeysCount > 20)
+                        return false;
+                    nOpCount += nKeysCount;
+                    if (nOpCount > 201)
+                        return false;
+                    int ikey = ++i;
+                    i += nKeysCount;
+                    if ((int)stack.size() < i)
+                        return false;
+
+                    int nSigsCount = CScriptNum(stacktop(-i)).getint();
+                    if (nSigsCount < 0 || nSigsCount > nKeysCount)
+                        return false;
+                    int isig = ++i;
+                    i += nSigsCount;
+                    if ((int)stack.size() < i)
+                        return false;
+
+                    // Subset of script starting at the most recent codeseparator
+                    CScript scriptCode(pbegincodehash, pend);
+
+                    // Drop the signatures, since there's no way for a signature to sign itself
+                    for (int k = 0; k < nSigsCount; k++)
+                    {
+                        valtype& vchSig = stacktop(-isig-k);
+                        scriptCode.FindAndDelete(CScript(vchSig));
+                    }
+
+                    bool fSuccess = true;
+                    while (fSuccess && nSigsCount > 0)
+                    {
+                        valtype& vchSig    = stacktop(-isig);
+                        valtype& vchPubKey = stacktop(-ikey);
+
+                        // Check signature
+                        bool fOk = IsCanonicalSignature(vchSig, flags) && IsCanonicalPubKey(vchPubKey, flags) &&
+                            CheckSig(vchSig, vchPubKey, scriptCode, txTo, nIn, nHashType, flags);
+
+                        if (fOk) {
+                            isig++;
+                            nSigsCount--;
+                        }
+                        ikey++;
+                        nKeysCount--;
+
+                        // If there are more signatures left than keys left,
+                        // then too many signatures have failed
+                        if (nSigsCount > nKeysCount)
+                            fSuccess = false;
+                    }
+
+                    // Clean up stack of actual arguments
+                    while (i-- > 1)
+                        popstack(stack);
+
+                    // A bug causes CHECKMULTISIG to consume one extra argument
+                    // whose contents were not checked in any way.
+                    //
+                    // Unfortunately this is a potential source of mutability,
+                    // so optionally verify it is exactly equal to zero prior
+                    // to removing it from the stack.
+                    if (stack.size() < 1)
+                        return false;
+                    if ((flags & SCRIPT_VERIFY_NULLDUMMY) && stacktop(-1).size())
+                        return error("CHECKMULTISIG dummy argument not null");
+                    popstack(stack);
+
+                    stack.push_back(fSuccess ? vchTrue : vchFalse);
+
+                    if (opcode == OP_CHECKMULTISIGVERIFY)
+                    {
+                        if (fSuccess)
+                            popstack(stack);
+                        else
+                            return false;
+                    }
+                }
+                break;
+
+                default:
+                    return false;
+            }
+
+            // Size limits
+            if (stack.size() + altstack.size() > 1000)
+                return false;
+        }
+    }
+    catch (...)
+    {
+        return false;
+    }
+
+    if (!vfExec.empty())
+        return false;
+
+    return true;
+}
+
+namespace {
+
+/** Wrapper that serializes like CTransaction, but with the modifications
+ *  required for the signature hash done in-place
+ */
+class CTransactionSignatureSerializer {
+private:
+    const CTransaction &txTo;  // reference to the spending transaction (the one being serialized)
+    const CScript &scriptCode; // output script being consumed
+    const unsigned int nIn;    // input index of txTo being signed
+    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
+
+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) {}
+
+    /** Serialize the passed scriptCode, skipping OP_CODESEPARATORs */
+    template<typename S>
+    void SerializeScriptCode(S &s, int nType, int nVersion) const {
+        CScript::const_iterator it = scriptCode.begin();
+        CScript::const_iterator itBegin = it;
+        opcodetype opcode;
+        unsigned int nCodeSeparators = 0;
+        while (scriptCode.GetOp(it, opcode)) {
+            if (opcode == OP_CODESEPARATOR)
+                nCodeSeparators++;
+        }
+        ::WriteCompactSize(s, scriptCode.size() - nCodeSeparators);
+        it = itBegin;
+        while (scriptCode.GetOp(it, opcode)) {
+            if (opcode == OP_CODESEPARATOR) {
+                s.write((char*)&itBegin[0], it-itBegin-1);
+                itBegin = it;
+            }
+        }
+        s.write((char*)&itBegin[0], it-itBegin);
+    }
+
+    /** Serialize an input of txTo */
+    template<typename S>
+    void SerializeInput(S &s, unsigned int nInput, int nType, int nVersion) const {
+        // In case of SIGHASH_ANYONECANPAY, only the input being signed is serialized
+        if (fAnyoneCanPay)
+            nInput = nIn;
+        // Serialize the prevout
+        ::Serialize(s, txTo.vin[nInput].prevout, nType, nVersion);
+        // Serialize the script
+        if (nInput != nIn)
+            // Blank out other inputs' signatures
+            ::Serialize(s, CScript(), nType, nVersion);
+        else
+            SerializeScriptCode(s, nType, nVersion);
+        // Serialize the nSequence
+        if (nInput != nIn && (fHashSingle || fHashNone))
+            // let the others update at will
+            ::Serialize(s, (int)0, nType, nVersion);
+        else
+            ::Serialize(s, txTo.vin[nInput].nSequence, nType, nVersion);
+    }
+
+    /** Serialize an output of txTo */
+    template<typename S>
+    void SerializeOutput(S &s, unsigned int nOutput, int nType, int nVersion) const {
+        if (fHashSingle && nOutput != nIn)
+            // Do not lock-in the txout payee at other indices as txin
+            ::Serialize(s, CTxOut(), nType, nVersion);
+        else
+            ::Serialize(s, txTo.vout[nOutput], nType, nVersion);
+    }
+
+    /** Serialize txTo */
+    template<typename S>
+    void Serialize(S &s, int nType, int nVersion) const {
+        // Serialize nVersion
+        ::Serialize(s, txTo.nVersion, nType, nVersion);
+        // Serialize vin
+        unsigned int nInputs = fAnyoneCanPay ? 1 : txTo.vin.size();
+        ::WriteCompactSize(s, nInputs);
+        for (unsigned int nInput = 0; nInput < nInputs; nInput++)
+             SerializeInput(s, nInput, nType, nVersion);
+        // Serialize vout
+        unsigned int nOutputs = fHashNone ? 0 : (fHashSingle ? nIn+1 : txTo.vout.size());
+        ::WriteCompactSize(s, nOutputs);
+        for (unsigned int nOutput = 0; nOutput < nOutputs; nOutput++)
+             SerializeOutput(s, nOutput, nType, nVersion);
+        // Serialie nLockTime
+        ::Serialize(s, txTo.nLockTime, nType, nVersion);
+    }
+};
+
+} // anon namespace
+
+uint256 SignatureHash(const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType)
+{
+    if (nIn >= txTo.vin.size()) {
+        LogPrintf("ERROR: SignatureHash() : nIn=%d out of range\n", nIn);
+        return 1;
+    }
+
+    // Check for invalid use of SIGHASH_SINGLE
+    if ((nHashType & 0x1f) == SIGHASH_SINGLE) {
+        if (nIn >= txTo.vout.size()) {
+            LogPrintf("ERROR: SignatureHash() : nOut=%d out of range\n", nIn);
+            return 1;
+        }
+    }
+
+    // Wrapper to serialize only the necessary parts of the transaction being signed
+    CTransactionSignatureSerializer txTmp(txTo, scriptCode, nIn, nHashType);
+
+    // Serialize and hash
+    CHashWriter ss(SER_GETHASH, 0);
+    ss << txTmp << nHashType;
+    return ss.GetHash();
+}
+
+// Valid signature cache, to avoid doing expensive ECDSA signature checking
+// twice for every transaction (once when accepted into memory pool, and
+// again when accepted into the block chain)
+class CSignatureCache
+{
+private:
+     // sigdata_type is (signature hash, signature, public key):
+    typedef boost::tuple<uint256, std::vector<unsigned char>, CPubKey> sigdata_type;
+    std::set< sigdata_type> setValid;
+    boost::shared_mutex cs_sigcache;
+
+public:
+    bool
+    Get(const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubKey)
+    {
+        boost::shared_lock<boost::shared_mutex> lock(cs_sigcache);
+
+        sigdata_type k(hash, vchSig, pubKey);
+        std::set<sigdata_type>::iterator mi = setValid.find(k);
+        if (mi != setValid.end())
+            return true;
+        return false;
+    }
+
+    void Set(const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubKey)
+    {
+        // DoS prevention: limit cache size to less than 10MB
+        // (~200 bytes per cache entry times 50,000 entries)
+        // Since there are a maximum of 20,000 signature operations per block
+        // 50,000 is a reasonable default.
+        int64_t nMaxCacheSize = GetArg("-maxsigcachesize", 50000);
+        if (nMaxCacheSize <= 0) return;
+
+        boost::unique_lock<boost::shared_mutex> lock(cs_sigcache);
+
+        while (static_cast<int64_t>(setValid.size()) > nMaxCacheSize)
+        {
+            // Evict a random entry. Random because that helps
+            // foil would-be DoS attackers who might try to pre-generate
+            // and re-use a set of valid signatures just-slightly-greater
+            // than our cache size.
+            uint256 randomHash = GetRandHash();
+            std::vector<unsigned char> unused;
+            std::set<sigdata_type>::iterator it =
+                setValid.lower_bound(sigdata_type(randomHash, unused, unused));
+            if (it == setValid.end())
+                it = setValid.begin();
+            setValid.erase(*it);
+        }
+
+        sigdata_type k(hash, vchSig, pubKey);
+        setValid.insert(k);
+    }
+};
+
+bool CheckSig(vector<unsigned char> vchSig, const vector<unsigned char> &vchPubKey, const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType, int flags)
+{
+    static CSignatureCache signatureCache;
+
+    CPubKey pubkey(vchPubKey);
+    if (!pubkey.IsValid())
+        return false;
+
+    // Hash type is one byte tacked on to the end of the signature
+    if (vchSig.empty())
+        return false;
+    if (nHashType == 0)
+        nHashType = vchSig.back();
+    else if (nHashType != vchSig.back())
+        return false;
+    vchSig.pop_back();
+
+    uint256 sighash = SignatureHash(scriptCode, txTo, nIn, nHashType);
+
+    if (signatureCache.Get(sighash, vchSig, pubkey))
+        return true;
+
+    if (!pubkey.Verify(sighash, vchSig))
+        return false;
+
+    if (!(flags & SCRIPT_VERIFY_NOCACHE))
+        signatureCache.Set(sighash, vchSig, pubkey);
+
+    return true;
+}
+
+bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CTransaction& txTo, unsigned int nIn,
+                  unsigned int flags, int nHashType)
+{
+    vector<vector<unsigned char> > stack, stackCopy;
+    if (!EvalScript(stack, scriptSig, txTo, nIn, flags, nHashType))
+        return false;
+    if (flags & SCRIPT_VERIFY_P2SH)
+        stackCopy = stack;
+    if (!EvalScript(stack, scriptPubKey, txTo, nIn, flags, nHashType))
+        return false;
+    if (stack.empty())
+        return false;
+
+    if (CastToBool(stack.back()) == false)
+        return false;
+
+    // Additional validation for spend-to-script-hash transactions:
+    if ((flags & SCRIPT_VERIFY_P2SH) && scriptPubKey.IsPayToScriptHash())
+    {
+        if (!scriptSig.IsPushOnly()) // scriptSig must be literals-only
+            return false;            // or validation fails
+
+        // stackCopy cannot be empty here, because if it was the
+        // P2SH  HASH <> EQUAL  scriptPubKey would be evaluated with
+        // an empty stack and the EvalScript above would return false.
+        assert(!stackCopy.empty());
+
+        const valtype& pubKeySerialized = stackCopy.back();
+        CScript pubKey2(pubKeySerialized.begin(), pubKeySerialized.end());
+        popstack(stackCopy);
+
+        if (!EvalScript(stackCopy, pubKey2, txTo, nIn, flags, nHashType))
+            return false;
+        if (stackCopy.empty())
+            return false;
+        return CastToBool(stackCopy.back());
+    }
+
+    return true;
+}
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
new file mode 100644
index 0000000000..0c6f8b9d13
--- /dev/null
+++ b/src/script/interpreter.h
@@ -0,0 +1,45 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2013 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef H_BITCOIN_SCRIPT_INTERPRETER
+#define H_BITCOIN_SCRIPT_INTERPRETER
+
+#include <vector>
+#include <stdint.h>
+#include <string>
+
+class uint256;
+class CScript;
+class CTransaction;
+
+/** Signature hash types/flags */
+enum
+{
+    SIGHASH_ALL = 1,
+    SIGHASH_NONE = 2,
+    SIGHASH_SINGLE = 3,
+    SIGHASH_ANYONECANPAY = 0x80,
+};
+
+/** Script verification flags */
+enum
+{
+    SCRIPT_VERIFY_NONE      = 0,
+    SCRIPT_VERIFY_P2SH      = (1U << 0), // evaluate P2SH (BIP16) subscripts
+    SCRIPT_VERIFY_STRICTENC = (1U << 1), // enforce strict conformance to DER and SEC2 for signatures and pubkeys
+    SCRIPT_VERIFY_LOW_S     = (1U << 2), // enforce low S values (<n/2) in signatures (depends on STRICTENC)
+    SCRIPT_VERIFY_NOCACHE   = (1U << 3), // do not store results in signature cache (but do query it)
+    SCRIPT_VERIFY_NULLDUMMY = (1U << 4), // verify dummy stack item consumed by CHECKMULTISIG is of zero-length
+};
+
+bool IsCanonicalPubKey(const std::vector<unsigned char> &vchPubKey, unsigned int flags);
+bool IsCanonicalSignature(const std::vector<unsigned char> &vchSig, unsigned int flags);
+
+uint256 SignatureHash(const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType);
+bool CheckSig(std::vector<unsigned char> vchSig, const std::vector<unsigned char> &vchPubKey, const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType, int flags);
+bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, const CTransaction& txTo, unsigned int nIn, unsigned int flags, int nHashType);
+bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CTransaction& txTo, unsigned int nIn, unsigned int flags, int nHashType);
+
+#endif