Test the exact order of CHECKMULTISIG sig/pubkey evaluation

Possible with STRICTENC

src/script/interpreter.cpp

@@ -855,6 +855,9 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                         valtype& vchSig    = stacktop(-isig);
                         valtype& vchPubKey = stacktop(-ikey);
 
+                        // Note how this makes the exact order of pubkey/signature evaluation
+                        // distinguishable by CHECKMULTISIG NOT if the STRICTENC flag is set.
+                        // See the script_(in)valid tests for details.
                         if (!CheckSignatureEncoding(vchSig, flags, serror) || !CheckPubKeyEncoding(vchPubKey, flags, serror)) {
                             // serror is set
                             return false;
@@ -871,7 +874,8 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, un
                         nKeysCount--;
 
                         // If there are more signatures left than keys left,
-                        // then too many signatures have failed
+                        // then too many signatures have failed. Exit early,
+                        // without checking any further signatures.
                         if (nSigsCount > nKeysCount)
                             fSuccess = false;
                     }

src/test/data/script_invalid.json

@@ -616,6 +616,25 @@ nSequences are max.
     "STRICTENC",
     "P2PK with undefined hashtype"
 ],
+
+["
+Order of CHECKMULTISIG evaluation tests, inverted by swapping the order of
+pubkeys/signatures so they fail due to the STRICTENC rules on validly encoded
+signatures and pubkeys.
+"],
+[
+    "0 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501",
+    "2 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 0 2 CHECKMULTISIG NOT",
+    "STRICTENC",
+    "2-of-2 CHECKMULTISIG NOT with the first pubkey invalid, and both signatures validly encoded."
+],
+[
+    "0 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501 0",
+    "2 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 2 CHECKMULTISIG NOT",
+    "STRICTENC",
+    "2-of-2 CHECKMULTISIG NOT with both pubkeys valid, but first signature invalid."
+],
+
 [
     "0x47 0x30440220166848cd5b82a32b5944d90de3c35249354b43773c2ece1844ee8d1103e2f6c602203b6b046da4243c77adef80ada9201b27bbfdf7f9d5428f40434b060432afd62005",
     "0x41 0x048282263212c609d9ea2a6e3e172de238d8c39cabd5ac1ca10646e23fd5f5150811f8a8098557dfe45e8256e830b60ace62d613ac2f7b17bed31b6eaff6e26caf CHECKSIG NOT",

src/test/data/script_valid.json

@@ -761,6 +761,31 @@ nSequences are max.
     "STRICTENC",
     "1-of-2 with the second 1 hybrid pubkey"
 ],
+
+["
+CHECKMULTISIG evaluation order tests. CHECKMULTISIG evaluates signatures and
+pubkeys in a specific order, and will exit early if the number of signatures
+left to check is greater than the number of keys left. As STRICTENC fails the
+script when it reaches an invalidly encoded signature or pubkey, we can use it
+to test the exact order in which signatures and pubkeys are evaluated by
+distinguishing CHECKMULTISIG returning false on the stack and the script as a
+whole failing.
+
+See also the corresponding inverted versions of these tests in script_invalid.json
+"],
+[
+    "0 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501",
+    "2 0 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 2 CHECKMULTISIG NOT",
+    "STRICTENC",
+    "2-of-2 CHECKMULTISIG NOT with the second pubkey invalid, and both signatures validly encoded. Valid pubkey fails, and CHECKMULTISIG exits early, prior to evaluation of second invalid pubkey."
+],
+[
+    "0 0 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501",
+    "2 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 2 CHECKMULTISIG NOT",
+    "STRICTENC",
+    "2-of-2 CHECKMULTISIG NOT with both pubkeys valid, but second signature invalid. Valid pubkey fails, and CHECKMULTISIG exits early, prior to evaluation of second invalid signature."
+],
+
 [
     "0x47 0x304402204649e9517ef0377a8f8270bd423053fd98ddff62d74ea553e9579558abbb75e4022044a2b2344469c12e35ed898987711272b634733dd0f5e051288eceb04bd4669e05",
     "0x41 0x048282263212c609d9ea2a6e3e172de238d8c39cabd5ac1ca10646e23fd5f5150811f8a8098557dfe45e8256e830b60ace62d613ac2f7b17bed31b6eaff6e26caf CHECKSIG",