On Tue, Oct 14, 2014 at 2:34 AM, Pieter Wuille <pieter.wui...@gmail.com> wrote: > Hi all, > > while working on a BIP62 implementation I discovered yet another type > of malleability: the interpretation of booleans. > > Any byte array with non-zero bytes in it (ignoring the highest bit of > the last byte, which is the sign bit when interpreting as a number) is > interpreted as true, anything else as false. Other than numbers, > they're not even restricted to 4 bytes. Worse, the code for dealing > with booleans is not very consistent: OP_BOOLAND and OP_BOOLOR first > interpret their arguments as numbers, and then compare them to 0 to > turn them into boolean values. > > This means that scripts that use booleans as inputs will be inherently > malleable. Given that that seems actually useful (passing in booleans > to guide some OP_IF's during execution of several alternatives), I > would like to change BIP62 to also state that interpreted booleans > must be of minimal encoded size (in addition to numbers). > > Any opinions for or against?
An argument against is that you can currently do something like this: OP_DUP OP_IF OP_HASH160 PUSH OP_EQUALVERIFY OP_ELSE <stuff> OP_CHECKSIGVERIFY OP_ENDIF E.g. if your input is non-zero you're giving a hash, if it's zero you're skipping that and running another branch. Of course you could just encode your script another way... but by that same logic you can 1 OP_QUALVERIFY to bool-ize any input in the true path. The inconsistency in handling makes it more likely that script authors will screw up with bad (for them) consequences, however. [I just asked pieter out of band to clarify if he means "minimal encoded size", or must be 0 or 1 minimally encoded... as the former doesn't fix the malleability, but the later is more disruptive] ------------------------------------------------------------------------------ Comprehensive Server Monitoring with Site24x7. Monitor 10 servers for $9/Month. Get alerted through email, SMS, voice calls or mobile push notifications. Take corrective actions from your mobile device. http://p.sf.net/sfu/Zoho _______________________________________________ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
