rich1.0npub1tjephawh7fdf6358jufuh5eyxwauzrjqa7qn50pglee4tayc2ntqcjtl6rhttps://nostr.ae/npub1tjephawh7fdf6358jufuh5eyxwauzrjqa7qn50pglee4tayc2ntqcjtl6rnjumphttps://nostr.ae📅 Original date posted:2016-01-07 📝 Original message:> "The problem case is where someone in a contract setup shows you a script, which you accept as being a payment to yourself. An attacker could use a collision attack to construct scripts with identical hashes, only one of which does have the property you want, and steal coins. > > So you really want collision security, and I don't think 80 bits is something we should encourage for that. Normal pubkey hashes don't have that problem, as they can't be constructed to pay to you." > > ... but I'm unconvinced: > > "But it is trivial for contract wallets to protect against collision attacks-- if you give me a script that is "gavin_pubkey CHECKSIG arbitrary_data OP_DROP" with "I promise I'm not trying to rip you off, just ignore that arbitrary data" a wallet can just refuse. Even more likely, a contract wallet won't even recognize that as a pay-to-gavin transaction. > > I suppose it could be looking for some form of "gavin_pubkey somebody_else_pubkey CHECKMULTISIG ... with the attacker using somebody_else_pubkey to force the collision, but, again, trivial contract protocol tweaks ("send along a proof you have the private key corresponding to the public key" or "everybody pre-commits pubkeys they'll use at protocol start") would protect against that. Yes, this is what I worry about. We're constructing a 2-of-2 multisig escrow in a contract. I reveal my public key A, you do a 80-bit search for B and C such that H(A and B) = H(B and C). You tell me your keys B, and I happily send to H(A and B), which you steal with H(B and C). Sending along a proof does not help, you can't prove that you do not know of a collision. Pre-committing does help, but is a very non-obvious security requirement, something I strongly believe is far riskier in practice. Bitcoin does have parts that rely on economic arguments for security or privacy, but can we please stick to using cryptography that is up to par for parts where we can? It's a small constant factor of data, and it categorically removes the worry about security levels. -- Pieter -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.linuxfoundation.org/pipermail/bitcoin-dev/attachments/20160108/e2e921fb/attachment.html>