NAME

       Data::Entropy - entropy (randomness) management

SYNOPSIS

               use Data::Entropy qw(entropy_source);

               $i = entropy_source->get_int(12345);

               use Data::Entropy qw(with_entropy_source);

               with_entropy_source $source, sub {
                       @a = shuffle(@a);
               };

DESCRIPTION

       This module maintains a concept of a current selection of entropy source.  Algorithms that require
       entropy, such as those in Data::Entropy::Algorithms, can use the source nominated by this module,
       avoiding the need for entropy source objects to be explicitly passed around.  This is convenient because
       usually one entropy source will be used for an entire program run and so an explicit entropy source
       parameter would rarely vary.  There is also a default entropy source, avoiding the need to explicitly
       configure a source at all.

       If nothing is done to set a source then it defaults to the use of Rijndael (AES) in counter mode (see
       Data::Entropy::RawSource::CryptCounter and Crypt::Rijndael), keyed using Perl's built-in "rand" function.
       This gives a data stream that looks like concentrated entropy, but really only has at most the entropy of
       the "rand" seed.  Within a single run it is cryptographically difficult to detect the correlation between
       parts of the pseudo-entropy stream.  If more true entropy is required then it is necessary to configure a
       different entropy source.

FUNCTIONS

       entropy_source
           Returns the current entropy source, a "Data::Entropy::Source" object.  This will be the source passed
           to the innermost call to "with_entropy_source", if any, or otherwise the default entropy source.

       with_entropy_source SOURCE, CLOSURE
           The SOURCE is selected, so that it will be returned by "entropy_source", and CLOSURE is called (with
           no arguments).  The SOURCE is selected only during the dynamic scope of the call; after CLOSURE
           finishes, by whatever means, the previously selected entropy source is restored.

           SOURCE is normally a "Data::Entropy::Source" object.  Alternatively, it may be "undef" to cause use
           of the default entropy source.  It may also be a reference to a function of no arguments, which will
           be called to generate the actual source only if required.  This avoids unnecessarily initialising the
           source object if it is uncertain whether any entropy will be required.  The source-generating closure
           may return a normal source or "undef", but not another function reference.

SEE ALSO

       Data::Entropy::Algorithms, Data::Entropy::Source

AUTHOR

       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

       Copyright (C) 2006, 2007, 2009, 2011 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself.