On Sun, Jan 7, 2018 at 3:16 PM, Pavol Rusnak via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote: > On 05/01/18 14:58, nullius via bitcoin-dev wrote: > I am currently drafting a new standard[1] which will allow also Shamir > Secret Scheme Splitting and there we disallow usage of a custom wordlist > in order to eradicate this mess. Will try to push this as BIP too once > we get it to the point we are OK with the contents. > > https://github.com/satoshilabs/slips/blob/master/slip-0039.md
This specification forces the key being used through a one way function, -- so you cannot take a pre-existing key and encode it with this scheme. The KDF it specifies is unconfigurable and fairly weak (20000xhmac-sha2-- which can be cracked at about 0.7M passwords a second on a single motherboard GPU cracker). The construction also will silently result in the user getting a different private key if they enter the wrong passphrase-- which could lead to funds loss. It is again, unversioned-- so it kinda of seems like it is intentionally constructed in a way that will prevent interoperable use, since the lack of versioning was a primary complaint from other perspective users. Of course, it fine if you want to make a trezor only thing, but why bother BIPing something that was not intended for interoperability? Even for a single vendor spec the lack of versioning seems to make things harder to support new key-related features such as segwit. The 16-bit "checksum" based on sha2 seems pretty poor since basing small checksums on a cryptographic hash results in a fairly poor checksum that is surprisingly likely to accept an errored string. Your wordlist is 10 bits and you have much less than 1023*10 bits of input, so you could easily have a 20 bit code (two words) which guaranteed that up to two errored words would always be detected, and probably could choose one which catches three words much more often 1:2^20 (sipa's crc tools can help find codes like this). The metadata seems to make fairly little affordance to help users avoid accidentally mixing shares from distinct sharings of the same key. Is it the idea that this is the only likely cause of a checksum error? (1:2^16 chance of silently returning the wrong key seems kinda bad). -- I'm not sure much could be done here, though, since additional payload is precious. As an aside, your specification might want to give some better advice about the SSS since my experience virtually everyone gets it wrong in ways that degrade or destroy its properties e.g. many fail to generate the additional coefficients of the polynominal randomly which results in insecurity (see armory for an example). Oh, also, I believe it is normally refereed to as "SSS" (three S)-- four S is the name of a linux program for secret sharing. I'm happy to see that there is no obvious way to abuse this one as a brainwallet scheme! _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
