[hashcash] hashcash for Jabber

JEP (Jabber Enhancement Proposal) #0158 mentions hashcash (or rather, a
variant of it) as a method for preventing IM spam (spim).

http://www.jabber.org/jeps/jep-0158.html

See section 6.2, in particular.

There are some differences between the variant of hashcash mentioned
there, and the one that we're all familiar with, although it uses the
same basic idea.

e.g.
- it uses SHA256 instead of SHA-1
- no special fields -- just the Jabber ID and "random" string are
  included
- instead of trying to get 0's as the most(?) significant bits, the
  receiver specifies a bitstring, and the sender tries to match those
  bits in the least significant bits of the hash

-- 
Hubert Chan <hubert@xxxxxxxxx> - http://www.uhoreg.ca/
PGP/GnuPG key: 1024D/124B61FA
Fingerprint: 96C5 012F 5F74 A5F7 1FF7  5291 AF29 C719 124B 61FA
Key available at wwwkeys.pgp.net.   Encrypted e-mail preferred.

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