[tahoe-dev] "Elk Point" design for mutable, add-only, and immutable files

[Zooko O'Whielacronx]

On Sat, Oct 10, 2009 at 9:25 PM, David-Sarah Hopwood
<david-sarah at jacaranda.org> wrote:
>
> OK, I've added everything I can think of right now.

:-)

> Note the question in footnote 5:
>
> # 5. Brute force costs assume a single-target attack that is expected to
> #    succeed with high probability. Costs will be lower for attacking
> #    multiple targets or for a lower success probability.
> #    (Should we give explicit formulae for this?)

We should think that issue through, along with the accompanying issue
of "how low a chance of success is low enough".  If there are 2^50
caps in use, and some technique can "attack all known caps at once",
then do we need to increase the size of the caps (possibly by up to 50
bits) to make it so that the chance of success against *any* target is
still negligible?  Or is it just unreasonable to think that some
adversary would spend massive amounts of computer power in order to
forge some random cap out of a large set of caps?  Anyway, writing
down precisely what things are susceptible to that sort of "shotgun"
attack seems necessary, which is why I added the "target" column.

Regards,

Zooko