Crypt::URandom(3p)

NAME
Crypt::URandom - Provide non blocking randomness

VERSION
This document describes Crypt::URandom version 0.55

SYNOPSIS
    use Crypt::URandom();

    my $random_string_50_bytes_long = Crypt::URandom::urandom(50);

OR

    use Crypt::URandom qw( urandom );

    my $random_string_50_bytes_long = urandom(50);

DESCRIPTION
This Module is intended to provide an interface to the strongest available source of non-blocking randomness on the current platform. Platforms currently supported are anything supporting getrandom(2), /dev/urandom and versions of Windows greater than or equal to Windows 2000.

SUBROUTINES/METHODS

"urandom"
    This function accepts an integer and returns a string of the same size filled with random data. It will throw an exception if the requested amount of random data is not returned. The first call will initialize the native cryptographic libraries (if necessary) and load all the required Perl libraries. This call is a buffered read on non Win32 platforms that do not support getrandom(2) or equivalent.

"urandom_ub"
    This function accepts an integer and returns a string of the same size filled with random data. It will throw an exception if the requested amount of random data is not returned. The first call will initialize the native cryptographic libraries (if necessary) and load all the required Perl libraries. This call is a unbuffered sysread on non Win32 platforms that do not support getrandom(2) or equivalent.

"getrandom"
    This function accepts an integer and returns a string of the same size filled with random data on platforms that implement getrandom(2). It will throw an exception if the requested amount of random data is not returned. This is NOT portable across all operating systems, but is made available if high-speed generation of random numbers is required. If an integer is not supplied as an argument, this function will return a empty string as a result (the same as if the integer 0 is supplied as an argument)

DIAGNOSTICS

"No secure alternative for random number generation for Win32 versions older than W2K"
    The module cannot run on versions of Windows earlier than Windows 2000 as there is no cryptographic functions provided by the operating system.

"Could not import CryptAcquireContext"
    The module was unable to load the CryptAcquireContextA function from the advapi32 dynamic library. The advapi32 library cannot probably be loaded.

"CryptAcquireContext failed"
    The module was unable to call the CryptAcquireContextA function from the advapi32 dynamic library.

"Could not import CryptGenRandom"
    The module was unable to load the CryptGenRandom function from the advapi32 dynamic library.

"Could not import SystemFunction036"
    The module was unable to load the SystemFunction036 function from the advapi32 dynamic library.

"The length argument must be supplied and must be an integer"
    The get method must be called with an integer argument to describe how many random bytes are required.

"CryptGenRandom failed"
    The Windows 2000 CryptGenRandom method call failed to generate the required amount of randomness

"RtlGenRand failed"
    The post Windows 2000 RtlGenRand method call failed to generate the required amount of randomness

"Only read n bytes from path"
    The /dev/urandom device did not return the desired amount of random bytes

"Failed to read from path"
    The /dev/urandom device returned an error when being read from

"Failed to open path"
    The /dev/urandom device returned an error when being opened

CONFIGURATION AND ENVIRONMENT
Crypt::URandom requires no configuration files or environment variables.

If the environment variable CRYPT_URANDOM_BUILD_DEBUG is specified when running "perl Makefile.PL" or "make test" AND getrandom(2) or it's equivalents cannot be detected, extra debug will be shown to show the failures to detect these functions.

DEPENDENCIES
    If the platform is Win32, the Win32::API module will be required. Otherwise no other modules other than those provided by perl will be required

INCOMPATIBILITIES
None reported.

BUGS AND LIMITATIONS
To report a bug, or view the current list of bugs, please visit <https://github.com/david-dick/crypt-urandom/issues>

AUTHOR
David Dick "<ddick@cpan.org>"

ACKNOWLEDGEMENTS
The Win32::API code for interacting with Microsoft's CryptoAPI <https://en.wikipedia.org/wiki/Microsoft_CryptoAPI> was copied with extreme gratitude from Crypt::Random::Source::Strong::Win32 by Max Kanat-Alexander <https://metacpan.org/author/MKANAT>

LICENSE AND COPYRIGHT
Copyright (c) 2025, David Dick "<ddick@cpan.org>". All rights reserved.

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

DISCLAIMER OF WARRANTY
BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.