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Old 03-21-2011, 08:08 PM
Aaron Toponce
 
Default Hashcash token does not represent bits calculated

Package: hashcash
Version: 1.21-1

According to the documentation, the hashcash binary supports the '-b
bits' switch and argument for calculating a hashcash token of the size
specified. The default size is 20 bits. The '-b' switch argument
supports an exact size, say '-b 40' for minting a 40 bit token, or
incrementing/decrementing the size from default, such as '-b +10' to
create an additional 10 bits from default (20). This should create a
token of 30 bits in size. Same holds for decrementing.

Consider the following example:

$ hashcash -m foo -Z 2
hashcash token: 1:20:110321:foo:MOAOyoyMfeKOPg7:5z7t

As per the 2nd column of the token, the default of 20 bits was used.
Let's increase to 30 bits:

$ hashcash -m foo -b 30 -Z 2
hashcash token: 1:20:110321:foo:PuJxVpBd5hjE+WX:7CR2

The 2nd colomn shows that only 20 bits were calculated, versus the 30
that I requested. This can be verified with SHA1 showing that the first
20 bits are zero, not the first 30:

$ echo -n 1:20:110321:foo:PuJxVpBd5hjE+WX:7CR2 | sha1sum
00000239da10b8f4cf3aadd15d62b2d0c261dc82 -

The same bug exists for incrementing and decrementing the bit size. The
2nd column should convey the bit size that I requested with '-b bits'
and verifying with SHA1 should show the firt few bits as zero, as
specified. Compare with a 44 bit token found at
http://hashcash.org/stamps/:

$ echo -n 1:44:070217:foo::xSi0bPjoswUh6h1Y:TMNI7 | sha1sum
000000000005ae959bd508c19ba300b1088410aa -

This is a Debian GNU/Linux unstable operating system running with:

2.6.37-1-686 #1 SMP Tue Feb 15 18:21:50 UTC 2011 i686 GNU/Linux

With C library version:

Version: 2.11.2-11

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