Merge pull request #5000

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

5 files changed, 25 insertions, 2 deletions

diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index cf81fe30a2..760086eaba 100644
--- a/src/script/interpreter.cpp
+++ b/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:
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
index 14cccc558f..12b2719414 100644
--- a/src/script/interpreter.h
+++ b/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);
diff --git a/src/script/script_error.cpp b/src/script/script_error.cpp
index 4a3df268ec..793fc0da41 100644
--- a/src/script/script_error.cpp
+++ b/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;
diff --git a/src/script/script_error.h b/src/script/script_error.h
index ae6626b257..21153f1bd1 100644
--- a/src/script/script_error.h
+++ b/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;
 
diff --git a/src/script/standard.h b/src/script/standard.h
index f3dcc75fdc..c4b82b4c45 100644
--- a/src/script/standard.h
+++ b/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;