Merge pull request #5000

0391423 Discourage NOPs reserved for soft-fork upgrades (Peter Todd)

src/script/interpreter.cpp

@@ -329,8 +329,14 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                 // Control
                 //
                 case OP_NOP:
+                break;
+
                 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:
+                {
+                    if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
+                        return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS);
+                }
                 break;
 
                 case OP_IF:

src/script/interpreter.h

@@ -57,7 +57,18 @@ enum
     // 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)
+    SCRIPT_VERIFY_MINIMALDATA = (1U << 6),
+
+    // Discourage use of NOPs reserved for upgrades (NOP1-10)
+    //
+    // Provided so that nodes can avoid accepting or mining transactions
+    // containing executed NOP's whose meaning may change after a soft-fork,
+    // thus rendering the script invalid; with this flag set executing
+    // discouraged NOPs fails the script. This verification flag will never be
+    // a mandatory flag applied to scripts in a block. NOPs that are not
+    // executed, e.g.  within an unexecuted IF ENDIF block, are *not* rejected.
+    SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS  = (1U << 7)
+
 };
 
 uint256 SignatureHash(const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType);

src/script/script_error.cpp

@@ -59,6 +59,8 @@ const char* ScriptErrorString(const ScriptError serror)
             return "Non-canonical signature: S value is unnecessarily high";
         case SCRIPT_ERR_SIG_NULLDUMMY:
             return "Dummy CHECKMULTISIG argument must be zero";
+        case SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS:
+            return "NOPx reserved for soft-fork upgrades";
         case SCRIPT_ERR_UNKNOWN_ERROR:
         case SCRIPT_ERR_ERROR_COUNT:
         default: break;

src/script/script_error.h

@@ -43,6 +43,9 @@ typedef enum ScriptError_t
     SCRIPT_ERR_SIG_HIGH_S,
     SCRIPT_ERR_SIG_NULLDUMMY,
 
+    /* softfork safeness */
+    SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS,
+
     SCRIPT_ERR_ERROR_COUNT
 } ScriptError;
 

src/script/standard.h

@@ -47,7 +47,8 @@ static const unsigned int MANDATORY_SCRIPT_VERIFY_FLAGS = SCRIPT_VERIFY_P2SH;
 static const unsigned int STANDARD_SCRIPT_VERIFY_FLAGS = MANDATORY_SCRIPT_VERIFY_FLAGS |
                                                          SCRIPT_VERIFY_STRICTENC |
                                                          SCRIPT_VERIFY_MINIMALDATA |
-                                                         SCRIPT_VERIFY_NULLDUMMY;
+                                                         SCRIPT_VERIFY_NULLDUMMY |
+                                                         SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS;
 
 /** For convenience, standard but not mandatory verify flags. */
 static const unsigned int STANDARD_NOT_MANDATORY_VERIFY_FLAGS = STANDARD_SCRIPT_VERIFY_FLAGS & ~MANDATORY_SCRIPT_VERIFY_FLAGS;

src/test/data/script_invalid.json

@@ -163,6 +163,23 @@ nSequences are max.
 ["1","NOP1 NOP2 NOP3 NOP4 NOP5 NOP6 NOP7 NOP8 NOP9 NOP10 2 EQUAL", "P2SH,STRICTENC"],
 ["'NOP_1_to_10' NOP1 NOP2 NOP3 NOP4 NOP5 NOP6 NOP7 NOP8 NOP9 NOP10","'NOP_1_to_11' EQUAL", "P2SH,STRICTENC"],
 
+["Ensure 100% coverage of discouraged NOPS"],
+["1", "NOP1",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP2",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP3",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP4",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP5",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP6",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP7",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP8",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP9",  "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+["1", "NOP10", "P2SH,DISCOURAGE_UPGRADABLE_NOPS"],
+
+["NOP10", "1", "P2SH,DISCOURAGE_UPGRADABLE_NOPS", "Discouraged NOP10 in scriptSig"],
+
+["1 0x01 0xb9", "HASH160 0x14 0x15727299b05b45fdaf9ac9ecf7565cfe27c3e567 EQUAL",
+ "P2SH,DISCOURAGE_UPGRADABLE_NOPS", "Discouraged NOP10 in redeemScript"],
+
 ["0x50","1", "P2SH,STRICTENC", "opcode 0x50 is reserved"],
 ["1", "IF 0xba ELSE 1 ENDIF", "P2SH,STRICTENC", "opcodes above NOP10 invalid if executed"],
 ["1", "IF 0xbb ELSE 1 ENDIF", "P2SH,STRICTENC"],

src/test/data/script_valid.json

@@ -235,6 +235,11 @@ nSequences are max.
 ["1","NOP1 NOP2 NOP3 NOP4 NOP5 NOP6 NOP7 NOP8 NOP9 NOP10 1 EQUAL", "P2SH,STRICTENC"],
 ["'NOP_1_to_10' NOP1 NOP2 NOP3 NOP4 NOP5 NOP6 NOP7 NOP8 NOP9 NOP10","'NOP_1_to_10' EQUAL", "P2SH,STRICTENC"],
 
+["1", "NOP", "P2SH,STRICTENC,DISCOURAGE_UPGRADABLE_NOPS", "Discourage NOPx flag allows OP_NOP"],
+
+["0", "IF NOP10 ENDIF 1", "P2SH,STRICTENC,DISCOURAGE_UPGRADABLE_NOPS",
+ "Discouraged NOPs are allowed if not executed"],
+
 ["0", "IF 0xba ELSE 1 ENDIF", "P2SH,STRICTENC", "opcodes above NOP10 invalid if executed"],
 ["0", "IF 0xbb ELSE 1 ENDIF", "P2SH,STRICTENC"],
 ["0", "IF 0xbc ELSE 1 ENDIF", "P2SH,STRICTENC"],

src/test/transaction_tests.cpp

@@ -37,7 +37,8 @@ static std::map<string, unsigned int> mapFlagNames = boost::assign::map_list_of
     (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);
+    (string("NULLDUMMY"), (unsigned int)SCRIPT_VERIFY_NULLDUMMY)
+    (string("DISCOURAGE_UPGRADABLE_NOPS"), (unsigned int)SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS);
 
 unsigned int ParseScriptFlags(string strFlags)
 {