[hashcash] Re: hashcash v1 questions

  • From: Hubert Chan <hubert@xxxxxxxxx>
  • To: hashcash@xxxxxxxxxxxxx
  • Date: Mon, 31 May 2004 23:16:56 -0400

>>>>> "Justin" == Justin Guyett <justin-hashcash@xxxxxxxx> writes:


Justin>   What's the point of including the bitcount?  That seems like a
Justin> completely inconsequential piece of information.  It could be a
Justin> lie, or a spammer could set it to the actual number of bits.

Since the bitcount is part of the token, you can't change the bitcount
without messing up the hash.  (i.e. the leading bits won't be 0 any

Justin> Why give end users the opportunity to create draconian mail
Justin> filtering rules?  If I send a stamp with a claimed value of 26
Justin> bits but there are only 24, and the recipient requires 22, what
Justin> are they going to do?  It's my fault for lying, but is the
Justin> hashcash header supposed to weed out compulsive liars or merely
Justin> test for proof of work?

It is to ensure that, if you require 22, and the sender creates a 20 bit
stamp, but gets lucky and gets a 22 bit stamp, the stamp will be treated
as only 20 bits.  (There is a 50% chance that a generated stamp will be
longer than the length attempted.)  There is no reason anyone would try
to claim that the stamp is longer than it really is.

Justin> This example is v0 with an advisory reverse-postage and sender
Justin> address/hostname added:

Justin> X:date:recip_resource:sender_postage:sender_resource:random

Justin> Is that really so lacking due to exclusion of an options field,
Justin> hash value/multi-puzzle indicator, and counter?  The 25 is
Justin> advisory only, and indicates the reverse-postage to the sender.
Justin> It's mentioned on the camram page.  Why is it not in hashcash v1
Justin> stamps?

You can add it using the extensions field.  I assume it's not in v1
because it's not required for proper operation of hashcash, and is

Hubert Chan <hubert@xxxxxxxxx> - http://www.uhoreg.ca/
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