[hashcash] Re: hashcash v1 questions
- From: Jonathan Morton <chromi@xxxxxxxxxxxxxxxxxxxxx>
- To: hashcash@xxxxxxxxxxxxx
- Date: Mon, 31 May 2004 22:23:14 +0100
The reason I'm looking for this tool is because camram white lists
folks
you've spoken with and white lists by name can be forged relatively
easily. I need a stronger mechanism to identify someone as familiar.
Absolutely. I like key-fingerprint-based whitelisting, but I don't
like
having keys in hashcash stamps. Generating a 25-bit collision on an
~1100
byte hashcash stamp would require nearly 4x the time necessary to
generate
the same 25-bit collision on a 64 byte stamp. Putting keys in hashcash
headers benefits those with insecure keys.
That may be the case for Adam's present naive implementation, but for
about the past week I've been hacking away at considerably more
efficient versions - see the "performance improvements" thread for the
gory details.
My present implementations have solving time independent of the stamp
length. We're presently discussing the possibility of adding padding -
yes, to a *longer* length - and optimising the minters for specific
stamp lengths which we can save a little (10-15%) work on.
My latest benchmark-du-jour:
Rate Name (* machine default)
1270323 ANSI Standard 1-pipe
Solution: 0:040404:foo@xxxxxxxx:0123456789abcdef0000000000001HDvz
Iterations: 21290621
Time taken: 16.760
2507729 PowerPC Altivec Standard 1x4-pipe
Solution: 0:040404:foo@xxxxxxxx:0123456789abcdef0000000000001HDvz
Iterations: 21290621
Time taken: 8.490
2507729 PowerPC Altivec Standard 2x4-pipe
Solution: 0:040404:foo@xxxxxxxx:0123456789abcdef0000000000001HDvz
Iterations: 21290621
Time taken: 8.490
2493046 PowerPC Altivec Compact 2x4-pipe *
Solution: 0:040404:foo@xxxxxxxx:0123456789abcdef0000000000001HDvz
Iterations: 21290621
Time taken: 8.540
--- AMD64/x86 MMX Compact 1x2-pipe (Not available on this
machine)
--- AMD64/x86 MMX Standard 1x2-pipe (Not available on this
machine)
The above is for a pre-selected 24-bit stamp on a 667MHz TiBook. For
comparison, hashcash-0.32 -s on the same machine:
speed: 599412 collision tests per second
time estimate: 26 seconds
--------------------------------------------------------------
from: Jonathan "Chromatix" Morton
mail: chromi@xxxxxxxxxxxxxxxxxxxxx
website: http://www.chromatix.uklinux.net/
tagline: The key to knowledge is not to rely on people to teach you it.
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