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).

1 files changed, 40 insertions, 11 deletions

diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index e463de8cc2..11c909472a 100644
--- a/src/script/interpreter.cpp
+++ b/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 bn2(stacktop(-1));
+                    CScriptNum bn1(stacktop(-2), fRequireMinimal);
+                    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 bn2(stacktop(-2));
-                    CScriptNum bn3(stacktop(-1));
+                    CScriptNum bn1(stacktop(-3), fRequireMinimal);
+                    CScriptNum bn2(stacktop(-2), fRequireMinimal);
+                    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;