Add SCRIPT_VERIFY_MINIMALDATA (BIP62 rules 3 and 4)

Also use the new flag as a standard rule, and replace the IsCanonicalPush
standardness check with it (as it is more complete).

src/main.cpp

@@ -633,10 +633,6 @@ bool IsStandardTx(const CTransaction& tx, string& reason)
             reason = "scriptsig-not-pushonly";
             return false;
         }
-        if (!txin.scriptSig.HasCanonicalPushes()) {
-            reason = "scriptsig-non-canonical-push";
-            return false;
-        }
     }
 
     unsigned int nDataOut = 0;

src/script/interpreter.cpp

@@ -157,6 +157,29 @@ bool static CheckPubKeyEncoding(const valtype &vchSig, unsigned int flags) {
     return true;
 }
 
+bool static CheckMinimalPush(const valtype& data, opcodetype opcode) {
+    if (data.size() == 0) {
+        // Could have used OP_0.
+        return opcode == OP_0;
+    } else if (data.size() == 1 && data[0] >= 1 && data[0] <= 16) {
+        // Could have used OP_1 .. OP_16.
+        return opcode == OP_1 + (data[0] - 1);
+    } else if (data.size() == 1 && data[0] == 0x81) {
+        // Could have used OP_1NEGATE.
+        return opcode == OP_1NEGATE;
+    } else if (data.size() <= 75) {
+        // Could have used a direct push (opcode indicating number of bytes pushed + those bytes).
+        return opcode == data.size();
+    } else if (data.size() <= 255) {
+        // Could have used OP_PUSHDATA.
+        return opcode == OP_PUSHDATA1;
+    } else if (data.size() <= 65535) {
+        // Could have used OP_PUSHDATA2.
+        return opcode == OP_PUSHDATA2;
+    }
+    return true;
+}
+
 bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker)
 {
     CScript::const_iterator pc = script.begin();
@@ -169,6 +192,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
     if (script.size() > 10000)
         return false;
     int nOpCount = 0;
+    bool fRequireMinimal = (flags & SCRIPT_VERIFY_MINIMALDATA) != 0;
 
     try
     {
@@ -205,9 +229,12 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                 opcode == OP_RSHIFT)
                 return false; // Disabled opcodes.
 
-            if (fExec && 0 <= opcode && opcode <= OP_PUSHDATA4)
+            if (fExec && 0 <= opcode && opcode <= OP_PUSHDATA4) {
+                if (fRequireMinimal && !CheckMinimalPush(vchPushValue, opcode)) {
+                    return false;
+                }
                 stack.push_back(vchPushValue);
-            else if (fExec || (OP_IF <= opcode && opcode <= OP_ENDIF))
+            } else if (fExec || (OP_IF <= opcode && opcode <= OP_ENDIF))
             switch (opcode)
             {
                 //
@@ -234,6 +261,8 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     // ( -- value)
                     CScriptNum bn((int)opcode - (int)(OP_1 - 1));
                     stack.push_back(bn.getvch());
+                    // The result of these opcodes should always be the minimal way to push the data
+                    // they push, so no need for a CheckMinimalPush here.
                 }
                 break;
 
@@ -458,7 +487,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     // (xn ... x2 x1 x0 n - ... x2 x1 x0 xn)
                     if (stack.size() < 2)
                         return false;
-                    int n = CScriptNum(stacktop(-1)).getint();
+                    int n = CScriptNum(stacktop(-1), fRequireMinimal).getint();
                     popstack(stack);
                     if (n < 0 || n >= (int)stack.size())
                         return false;
@@ -557,7 +586,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     // (in -- out)
                     if (stack.size() < 1)
                         return false;
-                    CScriptNum bn(stacktop(-1));
+                    CScriptNum bn(stacktop(-1), fRequireMinimal);
                     switch (opcode)
                     {
                     case OP_1ADD:       bn += bnOne; break;
@@ -590,8 +619,8 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     // (x1 x2 -- out)
                     if (stack.size() < 2)
                         return false;
-                    CScriptNum bn1(stacktop(-2));
+                    CScriptNum bn1(stacktop(-2), fRequireMinimal);
-                    CScriptNum bn2(stacktop(-1));
+                    CScriptNum bn2(stacktop(-1), fRequireMinimal);
                     CScriptNum bn(0);
                     switch (opcode)
                     {
@@ -635,9 +664,9 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     // (x min max -- out)
                     if (stack.size() < 3)
                         return false;
-                    CScriptNum bn1(stacktop(-3));
+                    CScriptNum bn1(stacktop(-3), fRequireMinimal);
-                    CScriptNum bn2(stacktop(-2));
+                    CScriptNum bn2(stacktop(-2), fRequireMinimal);
-                    CScriptNum bn3(stacktop(-1));
+                    CScriptNum bn3(stacktop(-1), fRequireMinimal);
                     bool fValue = (bn2 <= bn1 && bn1 < bn3);
                     popstack(stack);
                     popstack(stack);
@@ -727,7 +756,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     if ((int)stack.size() < i)
                         return false;
 
-                    int nKeysCount = CScriptNum(stacktop(-i)).getint();
+                    int nKeysCount = CScriptNum(stacktop(-i), fRequireMinimal).getint();
                     if (nKeysCount < 0 || nKeysCount > 20)
                         return false;
                     nOpCount += nKeysCount;
@@ -738,7 +767,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                     if ((int)stack.size() < i)
                         return false;
 
-                    int nSigsCount = CScriptNum(stacktop(-i)).getint();
+                    int nSigsCount = CScriptNum(stacktop(-i), fRequireMinimal).getint();
                     if (nSigsCount < 0 || nSigsCount > nKeysCount)
                         return false;
                     int isig = ++i;

src/script/interpreter.h

@@ -49,6 +49,13 @@ enum
 
     // Using a non-push operator in the scriptSig causes script failure (softfork safe, BIP62 rule 2).
     SCRIPT_VERIFY_SIGPUSHONLY = (1U << 5),
+
+    // Require minimal encodings for all push operations (OP_0... OP_16, OP_1NEGATE where possible, direct
+    // pushes up to 75 bytes, OP_PUSHDATA up to 255 bytes, OP_PUSHDATA2 for anything larger). Evaluating
+    // any other push causes the script to fail (BIP62 rule 3).
+    // In addition, whenever a stack element is interpreted as a number, it must be of minimal length (BIP62 rule 4).
+    // (softfork safe)
+    SCRIPT_VERIFY_MINIMALDATA = (1U << 6)
 };
 
 uint256 SignatureHash(const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType);

src/script/script.cpp

@@ -12,7 +12,7 @@ namespace {
 inline std::string ValueString(const std::vector<unsigned char>& vch)
 {
     if (vch.size() <= 4)
-        return strprintf("%d", CScriptNum(vch).getint());
+        return strprintf("%d", CScriptNum(vch, false).getint());
     else
         return HexStr(vch);
 }
@@ -238,33 +238,6 @@ bool CScript::IsPushOnly() const
     return true;
 }
 
-bool CScript::HasCanonicalPushes() const
-{
-    const_iterator pc = begin();
-    while (pc < end())
-    {
-        opcodetype opcode;
-        std::vector<unsigned char> data;
-        if (!GetOp(pc, opcode, data))
-            return false;
-        if (opcode > OP_16)
-            continue;
-        if (opcode < OP_PUSHDATA1 && opcode > OP_0 && (data.size() == 1 && data[0] <= 16))
-            // Could have used an OP_n code, rather than a 1-byte push.
-            return false;
-        if (opcode == OP_PUSHDATA1 && data.size() < OP_PUSHDATA1)
-            // Could have used a normal n-byte push, rather than OP_PUSHDATA1.
-            return false;
-        if (opcode == OP_PUSHDATA2 && data.size() <= 0xFF)
-            // Could have used an OP_PUSHDATA1.
-            return false;
-        if (opcode == OP_PUSHDATA4 && data.size() <= 0xFFFF)
-            // Could have used an OP_PUSHDATA2.
-            return false;
-    }
-    return true;
-}
-
 std::string CScript::ToString() const
 {
     std::string str;

src/script/script.h

@@ -192,10 +192,14 @@ public:
         m_value = n;
     }
 
-    explicit CScriptNum(const std::vector<unsigned char>& vch)
+    explicit CScriptNum(const std::vector<unsigned char>& vch, bool fRequireMinimal)
     {
-        if (vch.size() > nMaxNumSize)
+        if (vch.size() > nMaxNumSize) {
-            throw scriptnum_error("CScriptNum(const std::vector<unsigned char>&) : overflow");
+            throw scriptnum_error("script number overflow");
+        }
+        if (fRequireMinimal && vch.size() > 0 && (vch.back() & 0x7f) == 0 && (vch.size() <= 1 || (vch[vch.size() - 2] & 0x80) == 0)) {
+            throw scriptnum_error("non-minimally encoded script number");
+        }
         m_value = set_vch(vch);
     }
 
@@ -319,7 +323,6 @@ private:
     int64_t m_value;
 };
 
-
 /** Serialized script, used inside transaction inputs and outputs */
 class CScript : public std::vector<unsigned char>
 {
@@ -330,6 +333,10 @@ protected:
         {
             push_back(n + (OP_1 - 1));
         }
+        else if (n == 0)
+        {
+            push_back(OP_0);
+        }
         else
         {
             *this << CScriptNum::serialize(n);
@@ -554,9 +561,6 @@ public:
     // Called by IsStandardTx and P2SH/BIP62 VerifyScript (which makes it consensus-critical).
     bool IsPushOnly() const;
 
-    // Called by IsStandardTx.
-    bool HasCanonicalPushes() const;
-
     // Returns whether the script is guaranteed to fail at execution,
     // regardless of the initial stack. This allows outputs to be pruned
     // instantly when entering the UTXO set.

src/script/standard.h

@@ -41,6 +41,7 @@ static const unsigned int MANDATORY_SCRIPT_VERIFY_FLAGS = SCRIPT_VERIFY_P2SH;
 // blocks and we must accept those blocks.
 static const unsigned int STANDARD_SCRIPT_VERIFY_FLAGS = MANDATORY_SCRIPT_VERIFY_FLAGS |
                                                          SCRIPT_VERIFY_STRICTENC |
+                                                         SCRIPT_VERIFY_MINIMALDATA |
                                                          SCRIPT_VERIFY_NULLDUMMY;
 
 // For convenience, standard but not mandatory verify flags.

src/test/data/script_invalid.json

@@ -384,6 +384,10 @@ nSequences are max.
 
 ["0x00", "'00' EQUAL", "P2SH,STRICTENC", "Basic OP_0 execution"],
 
+["1 IF 0x01 0x81 ENDIF 1", "", "MINIMALDATA", "evaluated non-minimal data"],
+["1 IF 0x01 0x05 ENDIF 1", "", "MINIMALDATA", "evaluated non-minimal data"],
+["1 IF 0x4c 0x03 0x222222 ENDIF 1", "", "MINIMALDATA", "evaluated non-minimal data"],
+
 [
     "0x47 0x30440220304eff7556bba9560df47873275e64db45f3cd735998ce3f00d2e57b1bb5f31302205c0c9d14b8b80d43e2ac9b87532f1af6d8a3271262bc694ec4e14068392bb0a001",
     "0x41 0x0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8 CHECKSIG",

src/test/data/script_valid.json

@@ -529,6 +529,33 @@ nSequences are max.
 
 ["0x00", "SIZE 0 EQUAL", "P2SH,STRICTENC", "Basic OP_0 execution"],
 
+["0x01 0x81", "0x4f EQUAL", "", "direct push of 0x81 equals 1NEGATE"],
+["0x01 0x05", "5 EQUAL", "", "direct push of 0x05 equals 5"],
+["0x4c 0x4b 0x111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111", "0x4b 0x111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 EQUAL", "", "PUSHDATA1 of 75 bytes equals direct push of it"],
+["0x4d 0xFF00 0x111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111", "0x4c 0xFF 0x111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 EQUAL", "", "PUSHDATA2 of 255 bytes equals PUSHDATA1 of it"],
+["0x02 0x8000", "128 NUMEQUAL", "", "0x8000 equals 128"],
+["0x01 0x00", "0 NUMEQUAL", "", "0x00 numequals 0"],
+["0x01 0x80", "0 NUMEQUAL", "", "0x80 (negative zero) numequals 0"],
+["0x02 0x0080", "0 NUMEQUAL", "", "0x0080 numequals 0"],
+["0x02 0x0500", "5 NUMEQUAL", "", "0x0500 numequals 5"],
+["0x03 0xff7f80", "0x02 0xffff NUMEQUAL", "", ""],
+["0x03 0xff7f00", "0x02 0xff7f NUMEQUAL", "", ""],
+["0x04 0xffff7f80", "0x03 0xffffff NUMEQUAL", "", ""],
+["0x04 0xffff7f00", "0x03 0xffff7f NUMEQUAL", "", ""],
+["0 IF 0x01 0x81 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x01 0x05 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x02 0x8000 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x01 0x00 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x01 0x80 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x02 0x0080 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x02 0x0400 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x03 0xff7f80 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x03 0xff7f00 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x04 0xffff7f80 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x04 0xffff7f00 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+["0 IF 0x4c 0x03 0x222222 ENDIF 1", "", "MINIMALDATA", "unevaluated non-minimal data"],
+
+
 [
     "0x47 0x3044022007415aa37ce7eaa6146001ac8bdefca0ddcba0e37c5dc08c4ac99392124ebac802207d382307fd53f65778b07b9c63b6e196edeadf0be719130c5db21ff1e700d67501",
     "0x41 0x0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8 CHECKSIG",
@@ -638,13 +665,13 @@ nSequences are max.
     "P2PK NOT with invalid sig and undefined hashtype but no STRICTENC"
 ],
 [
-    "0x01 0x01 0x47 0x3044022046ce33d1771b0127dd4c4cef8fdc3218ebdfa60e3793ed700292d8ebd93fb1f402201029d47a414db83e96e31443c2d8b552f971469c4800f5eff7df2f0648521aed01 0x47 0x304402205c53911ad55b054920043962bbda98cf6e57e2db1cd5611138251490baabaa8702201dc80dfceae6007e7772dc13ff6e7ca66a983cb017fe5d46d30118462d83bcf801 0x47 0x304402201937e44a4ec12364f9d32f9d25e7ecbc68aee9ef90069af80efef4c05f6ace9602206c515101c00c75710b32ff7ff8dbaf7c9a0be6e86ed14a0755b47626604f31fd01",
+    "1 0x47 0x3044022046ce33d1771b0127dd4c4cef8fdc3218ebdfa60e3793ed700292d8ebd93fb1f402201029d47a414db83e96e31443c2d8b552f971469c4800f5eff7df2f0648521aed01 0x47 0x304402205c53911ad55b054920043962bbda98cf6e57e2db1cd5611138251490baabaa8702201dc80dfceae6007e7772dc13ff6e7ca66a983cb017fe5d46d30118462d83bcf801 0x47 0x304402201937e44a4ec12364f9d32f9d25e7ecbc68aee9ef90069af80efef4c05f6ace9602206c515101c00c75710b32ff7ff8dbaf7c9a0be6e86ed14a0755b47626604f31fd01",
     "3 0x21 0x0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798 0x21 0x038282263212c609d9ea2a6e3e172de238d8c39cabd5ac1ca10646e23fd5f51508 0x21 0x03363d90d447b00c9c99ceac05b6262ee053441c7e55552ffe526bad8f83ff4640 3 CHECKMULTISIG",
     "",
     "3-of-3 with nonzero dummy but no NULLDUMMY"
 ],
 [
-    "0x01 0x01 0x47 0x30440220195038dbc6b2ae1199f86a6777824f7c5149789d85f655a3534a4422b8fba38c02204df9db87d2eb9fe06edc66870d9ac4c9ce673459f9d43cee0347ce4ffb02ee5a01 0x47 0x3044022010a45f30c6fa97a186eba9e6b595ab87d3dfcbf05dcaf1f1b8e3e7bf39515bb802203474e78d3d372e5f5c0f8c257ce8300c4bb8f37c51d4a894e11a91b5817da6ed01 0x47 0x30440220039cffd8e39850f95112662b1220b14b3c0d3d8a2772e13c947bfbf96345a64e02204154bfa77e2c0134d5434353bed82141e5da1cc479954aa288d5f0671480a04b01",
+    "1 0x47 0x30440220195038dbc6b2ae1199f86a6777824f7c5149789d85f655a3534a4422b8fba38c02204df9db87d2eb9fe06edc66870d9ac4c9ce673459f9d43cee0347ce4ffb02ee5a01 0x47 0x3044022010a45f30c6fa97a186eba9e6b595ab87d3dfcbf05dcaf1f1b8e3e7bf39515bb802203474e78d3d372e5f5c0f8c257ce8300c4bb8f37c51d4a894e11a91b5817da6ed01 0x47 0x30440220039cffd8e39850f95112662b1220b14b3c0d3d8a2772e13c947bfbf96345a64e02204154bfa77e2c0134d5434353bed82141e5da1cc479954aa288d5f0671480a04b01",
     "3 0x21 0x0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798 0x21 0x038282263212c609d9ea2a6e3e172de238d8c39cabd5ac1ca10646e23fd5f51508 0x21 0x03363d90d447b00c9c99ceac05b6262ee053441c7e55552ffe526bad8f83ff4640 3 CHECKMULTISIG NOT",
     "",
     "3-of-3 NOT with invalid sig and nonzero dummy but no NULLDUMMY"

src/test/script_tests.cpp

@@ -179,7 +179,7 @@ public:
     TestBuilder& Num(int num)
     {
         DoPush();
-        spendTx.vin[0].scriptSig << CScriptNum(num);
+        spendTx.vin[0].scriptSig << num;
         return *this;
     }
 
@@ -788,19 +788,19 @@ BOOST_AUTO_TEST_CASE(script_combineSigs)
 
 BOOST_AUTO_TEST_CASE(script_standard_push)
 {
-    for (int i=0; i<1000; i++) {
+    for (int i=0; i<67000; i++) {
         CScript script;
         script << i;
         BOOST_CHECK_MESSAGE(script.IsPushOnly(), "Number " << i << " is not pure push.");
-        BOOST_CHECK_MESSAGE(script.HasCanonicalPushes(), "Number " << i << " push is not canonical.");
+        BOOST_CHECK_MESSAGE(VerifyScript(script, CScript() << OP_1, SCRIPT_VERIFY_MINIMALDATA, BaseSignatureChecker()), "Number " << i << " push is not minimal data.");
     }
 
-    for (int i=0; i<1000; i++) {
+    for (unsigned int i=0; i<=MAX_SCRIPT_ELEMENT_SIZE; i++) {
         std::vector<unsigned char> data(i, '\111');
         CScript script;
         script << data;
         BOOST_CHECK_MESSAGE(script.IsPushOnly(), "Length " << i << " is not pure push.");
-        BOOST_CHECK_MESSAGE(script.HasCanonicalPushes(), "Length " << i << " push is not canonical.");
+        BOOST_CHECK_MESSAGE(VerifyScript(script, CScript() << OP_1, SCRIPT_VERIFY_MINIMALDATA, BaseSignatureChecker()), "Length " << i << " push is not minimal data.");
     }
 }
 

src/test/scriptnum_tests.cpp

@@ -25,11 +25,11 @@ static void CheckCreateVch(const int64_t& num)
     BOOST_CHECK(verify(bignum, scriptnum));
 
     CBigNum bignum2(bignum.getvch());
-    CScriptNum scriptnum2(scriptnum.getvch());
+    CScriptNum scriptnum2(scriptnum.getvch(), false);
     BOOST_CHECK(verify(bignum2, scriptnum2));
 
     CBigNum bignum3(scriptnum2.getvch());
-    CScriptNum scriptnum3(bignum2.getvch());
+    CScriptNum scriptnum3(bignum2.getvch(), false);
     BOOST_CHECK(verify(bignum3, scriptnum3));
 }
 

src/test/transaction_tests.cpp

@@ -34,6 +34,7 @@ static std::map<string, unsigned int> mapFlagNames = boost::assign::map_list_of
     (string("DERSIG"), (unsigned int)SCRIPT_VERIFY_DERSIG)
     (string("LOW_S"), (unsigned int)SCRIPT_VERIFY_LOW_S)
     (string("SIGPUSHONLY"), (unsigned int)SCRIPT_VERIFY_SIGPUSHONLY)
+    (string("MINIMALDATA"), (unsigned int)SCRIPT_VERIFY_MINIMALDATA)
     (string("NULLDUMMY"), (unsigned int)SCRIPT_VERIFY_NULLDUMMY);
 
 unsigned int ParseScriptFlags(string strFlags)