NAME
    Digest::Hashcash - generate Hashcashes (http://www.hashcash.org)

SYNOPSIS
     use Digest::Hashcash;

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

    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 http://gcc.gnu.org/ :)

    $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".

SEE ALSO
    <http://www.hashcash.org>.

SUPPORT FOR THE PERL MULTICORE SPECIFICATION
    This module supports the perl multicore specification
    (<http://perlmulticore.schmorp.de/>) for token generation of any length
    and size.

BUGS
     * 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 :(

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de