Data::Entropy(3)

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);
        };

STATUS
This module is deprecated.

For most purposes (including cryptography and security), modules like Crypt::URandom, Crypt::SysRandom or Crypt::PRNG are more than adequate.

Modern operating systems provide good sources of random bytes, and the above mentioned modules work on many kinds of systems, including Windows.

There is no need to choose an entropy source, and some users of this module have omitted that step, and prior to version 0.008 they may have been relying on Perl's builtin "rand" function.

Please see CPAN Author's Guide to Random Data for Security <https://security.metacpan.org/docs/guides/random-data-for-security.html>.

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 Crypt::URandom.

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>

Maintained by Robert Rothenberg <perl@rhizomnic.com>

COPYRIGHT
Copyright (C) 2006, 2007, 2009, 2011, 2025-2026 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.