Digest::Hashcash - generate Hashcashes (


 use Digest::Hashcash;


This module implements the hashcash hash (or digest, although it's not clearly a digest). For all your information needs please visit

One thing to note about this module is that it requires ISO C99 support, both in your compiler and your standard library. If you don't have a compiler that supports ISO C, get gcc at :)

$secs = estimate_time $size

Estimate the average time necessary to calculate a token of the given size.

See also estimate_size.

$size = estimate_size $time[, $min]

Estimate the size that can be calculated in the given time (which is an upper bound). The function will not return a size less then min.

Estimating the time to be used can go wrong by as much as 50% (but is usually quite accurate), and the estimation itself can take as much as a second on slower (<pentium) machines, but faster machines (1Ghz P3 for example) usually handle it within a hundredth of a second or so.

The estimation will be done only once, so you can call this fucntion as often as you like without incuring the overhead everytime.

$cipher = new Digest::Hashcash [param => value...]
size => 18

The number of collisions, in bits. Every bit increases the time to create the token (and thus the cash) by two.

uid => ""

A string used to make the token more unique (e.g. the senders address) and reduce token collisions. The string must only contain characters valid for the trial part of the token, e.g. uuencoded, base64 or e-mail-address-parts are useful here.

extrarand => 0

The extra bytes of randomness to add to the token in addition to the standard amount. Each byte adds a little bit over 6 bit of randomness to the token.

The standard amount of randomness is 8 (> 51 bits of randomness).

timestamp => 0

The timestamp to use. A value of 0 (the default) means to use the current time.

$token = $cipher->hash ($data [, param => value...])

Creates and returns a new token. This can take some time.

Any additional parameters are interpreted the same way as arguments to new.

$prefix = $cipher->verify ($token [, param => value...]))

Checks the given token and returns true if the token has the minimum number of prefix bits, or false otherwise. The value returned is actually the number of collisions, so to find the number of collisions bits specify collisions => 0.

Any additional parameters are interpreted the same way as arguments to new.

$resource = $cipher->resource ($token)

Returns the resource part, or undef.

$tstamp = $ciper->timestamp ($token)

Returns the timestamp part (in the same format as perl's time), or undef.



This module supports the perl multicore specification (<>) for token generation of any length and size.


 * There is a y2k+100 problem, as I always assume the same as Time::Local.
   This is a problem with the hashcash specification, which specifies
   years as 2 digits :(


 Marc Lehmann <>