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.\" ========================================================================
.\"
.IX Title "Data::Entropy 3pm"
.TH Data::Entropy 3pm "2022-06-12" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
Data::Entropy \- entropy (randomness) management
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&        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);
\&        };
.Ve
.SH "DESCRIPTION"
.IX Header "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.
.PP
If nothing is done to set a source then it defaults to the use of Rijndael
(\s-1AES\s0) in counter mode (see Data::Entropy::RawSource::CryptCounter
and Crypt::Rijndael), keyed using Perl's built-in \f(CW\*(C`rand\*(C'\fR function.
This gives a data stream that looks like concentrated entropy, but really
only has at most the entropy of the \f(CW\*(C`rand\*(C'\fR 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.
.SH "FUNCTIONS"
.IX Header "FUNCTIONS"
.IP "entropy_source" 4
.IX Item "entropy_source"
Returns the current entropy source, a \f(CW\*(C`Data::Entropy::Source\*(C'\fR
object.  This will be the source passed to the innermost call to
\&\f(CW\*(C`with_entropy_source\*(C'\fR, if any, or otherwise the default entropy source.
.IP "with_entropy_source \s-1SOURCE, CLOSURE\s0" 4
.IX Item "with_entropy_source SOURCE, CLOSURE"
The \s-1SOURCE\s0 is selected, so that it will be returned by \f(CW\*(C`entropy_source\*(C'\fR,
and \s-1CLOSURE\s0 is called (with no arguments).  The \s-1SOURCE\s0 is selected only
during the dynamic scope of the call; after \s-1CLOSURE\s0 finishes, by whatever
means, the previously selected entropy source is restored.
.Sp
\&\s-1SOURCE\s0 is normally a \f(CW\*(C`Data::Entropy::Source\*(C'\fR object.  Alternatively,
it may be \f(CW\*(C`undef\*(C'\fR 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 \f(CW\*(C`undef\*(C'\fR, but not another function reference.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Data::Entropy::Algorithms,
Data::Entropy::Source
.SH "AUTHOR"
.IX Header "AUTHOR"
Andrew Main (Zefram) <zefram@fysh.org>
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2006, 2007, 2009, 2011
Andrew Main (Zefram) <zefram@fysh.org>
.SH "LICENSE"
.IX Header "LICENSE"
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.