Proof-of-work, just like Bitcoin itself uses for hashing? See hashcash as well. Require that the message in question is hashed together with a random value, with an output that matches a given pattern. And specify that one part of the message has to be the hash of a Bitcoin block from the given time period.
- Sent from my phone Den 11 nov 2013 17:43 skrev "CodesInChaos" <codesinch...@gmail.com>: > On Sun, Nov 10, 2013 at 9:54 AM, Andy Isaacson <a...@hexapodia.org> wrote: > > For example, suppose you use the low bits of the bitcoin blockchain > > hash. An attacker with 10% of the hash power could probabilistically > > attack such a system by chosing blocks with a specific value in those > > bits; > > This can be avoided by running a sequential computation based on that > hash. For example > by hashing it 2^40 times. Obvious downside is that verifying that the > computation was performed > correctly is just as expensive (but parallelizable). > > Perhaps there is a function that's sequential and slow in one > direction and fast in the reverse direction. > _______________________________________________ > cryptography mailing list > cryptography@randombit.net > http://lists.randombit.net/mailman/listinfo/cryptography >
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