data::entropy(3pm) [debian man page]

Data::Entropy(3pm)					User Contributed Perl Documentation					Data::Entropy(3pm)

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.

perl v5.12.3							    2011-05-09							Data::Entropy(3pm)

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RANDOM(4)						   BSD Kernel Interfaces Manual 						 RANDOM(4)

NAME

     random , urandom -- random data source devices.

SYNOPSIS

     pseudo-device random

DESCRIPTION

     The random device produces uniformly distributed random byte values of potentially high quality.

     To obtain random bytes, open /dev/random for reading and read from it.

     To add entropy to the random generation system, open /dev/random for writing and write data that you believe to be somehow random.

     /dev/urandom is a compatibility nod to Linux. On Linux, /dev/urandom will produce lower quality output if the entropy pool drains, while
     /dev/random will prefer to block and wait for additional entropy to be collected.	With Yarrow, this choice and distinction is not necessary,
     and the two devices behave identically. You may use either.

OPERATION

     The random device implements the Yarrow pseudo random number generator algorithm and maintains its entropy pool.  Additional entropy is fed
     to the generator regularly by the SecurityServer daemon from random jitter measurements of the kernel.  SecurityServer is also responsible
     for periodically saving some entropy to disk and reloading it during startup to provide entropy in early system operation.

     You may feed additional entropy to the generator by writing it to the random device, though this is not required in a normal operating envi-
     ronment.

LIMITATIONS AND WARNINGS

     Yarrow is a fairly resilient algorithm, and is believed to be resistant to non-root.  The quality of its output is however dependent on regu-
     lar addition of appropriate entropy. If the SecurityServer system daemon fails for any reason, output quality will suffer over time without
     any explicit indication from the random device itself.

     Paranoid programmers can counteract this risk somewhat by collecting entropy of their choice (e.g. from keystroke or mouse timings) and seed-
     ing it into random directly before obtaining important random numbers.

FILES

     /dev/random
     /dev/urandom

HISTORY

     A random device appeared in the Linux operating system.

Darwin								 September 6, 2001							    Darwin

Linux and UNIX Man Pages

data::entropy(3pm) [debian man page]

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