Discourage NOPs reserved for soft-fork upgrades

NOP1 to NOP10 are reserved for future soft-fork upgrades. In the event
of an upgrade such NOPs have *VERIFY behavior, meaning that if their
arguments are not correct the script fails. Discouraging these NOPs by
rejecting transactions containing them from the mempool ensures that
we'll never accept transactions, nor mine blocks, with scripts that are
now invalid according to the majority of hashing power even if we're not
yet upgraded. Previously this wasn't an issue as the IsStandard() rules
didn't allow upgradable NOPs anyway, but 7f3b4e95 relaxed the
IsStandard() rules for P2SH redemptions allowing any redeemScript to be
spent.

We *do* allow upgradable NOPs in scripts so long as they are not
executed. This is harmless as there is no opportunity for the script to
be invalid post-upgrade.

3 files changed, 24 insertions, 1 deletions

diff --git a/src/test/data/script_invalid.json b/src/test/data/script_invalid.json
index 6f451a36ee..0356d0be1c 100644
--- a/src/test/data/script_invalid.json
+++ b/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"],
diff --git a/src/test/data/script_valid.json b/src/test/data/script_valid.json
index 439c82ef32..0cf1563163 100644
--- a/src/test/data/script_valid.json
+++ b/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"],
diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp
index bf3a60c04f..e939e89972 100644
--- a/src/test/transaction_tests.cpp
+++ b/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)
 {