Re: stamp collisions

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On Tue, 31 Aug 2004, Hubert Chan wrote:

> Yes.  That's why you still need the sender=<email address> extension.
>
> Anyways, I feel pretty safe using a resolution that's on the order of 
> one day.  But for people really worried about collisions, that's one 
> thing that you can do.  Even if the date in the stamp stays with a 
> one-day resolution, you can add a time value as an extension.
============

i'm not entirely sure why i don't like that extension... maybe because it 
makes the header bigger...? maybe because it can be used for "joe 
jobs"...?


> OK, it doesn't have to be sequential then.  Use a pseudo-random number 
> generator with a large cycle length and that depends on your own secret 
> key.
>
> (of course, having this "counter" also requires that hashcash save the 
> seed/counter value between runs, which probably should be avoided.)
=============

what you're describing is similar to GnuPG's "random_seed" file, and that 
does seem like overkill for hashcash.

the three simple sources of "entropy" that i see for seeding a PRNG (in 
addition to system entropy):
  1) use the sender's address (or it's hash)
  2) hash the double-spend database file
  3) create a file in the yet-to-be-created (hint) config directory and 
fill the file with random stuff... similar to ezmlm's "key" file. this 
only has to be created when hashcash is first used*.

any one of these should reduce the risk of doppelganger stamps being 
created during the same second, but i'm partial to either 1 or 1+2.

* it might seem tempting to fill this file during installation, but if a 
machine comes with hashcash installed at the factory, then all machines 
leaving that factory might have the same "entropy file", and it would be 
somewhat self defeating.


  	...atom

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