3
The reference Bitcoin client disables several script commands (the programming within a transaction) due to possible implementation issues in the network. I think it's possible that a forked client may actually enable such commands.
I'd like to test and compare my implementation against others.
2
Yes.
The bitcoin implementation of banned opcodes is in script.cpp:
if (opcode == OP_CAT ||
opcode == OP_SUBSTR ||
opcode == OP_LEFT ||
opcode == OP_RIGHT ||
opcode == OP_INVERT ||
opcode == OP_AND ||
opcode == OP_OR ||
opcode == OP_XOR ||
opcode == OP_2MUL ||
opcode == OP_2DIV ||
opcode == OP_MUL ||
opcode == OP_DIV ||
opcode == OP_MOD ||
opcode == OP_LSHIFT ||
opcode == OP_RSHIFT)
return false;
Note that this is not a complete list - OP_NOTEQUAL is also disabled. This code struck me oddly because it appears to create a fork with transactions that use OP_NOTEQUAL. (Perhaps it wasn't being used.)
// OP_NOTEQUAL is disabled because it would be too easy to say
// something like n != 1 and have some wiseguy pass in 1 with extra
// zero bytes after it (numerically, 0x01 == 0x0001 == 0x000001)
//if (opcode == OP_NOTEQUAL)
// fEqual = !fEqual;
You didn't ask about it, but it's also the same.
