Add HasCanonicalPushes(), and use it in IsStandardTx

Author: sipa

src/main.cpp

@@ -442,6 +442,10 @@ bool IsStandardTx(const CTransaction& tx, string& reason)
             reason = "scriptsig-not-pushonly";
             return false;
         }
+        if (!txin.scriptSig.HasCanonicalPushes()) {
+            reason = "non-canonical-push";
+            return false;
+        }
     }
 
     unsigned int nDataOut = 0;

src/script.cpp

@@ -1881,6 +1881,33 @@ 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;
+}
+
 class CScriptVisitor : public boost::static_visitor<bool>
 {
 private:

src/script.h

@@ -541,9 +541,12 @@ class CScript : public std::vector<unsigned char>
 
     bool IsPayToScriptHash() const;
 
-    // Called by IsStandardTx
+    // Called by IsStandardTx and P2SH 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/test/script_tests.cpp

@@ -438,4 +438,22 @@ BOOST_AUTO_TEST_CASE(script_combineSigs)
     BOOST_CHECK(combined == partial3c);
 }
 
+BOOST_AUTO_TEST_CASE(script_standard_push)
+{
+    for (int i=0; i<1000; 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.");
+    }
+
+    for (int i=0; i<1000; 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_AUTO_TEST_SUITE_END()