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


Data::Entropy::RawSource::Local - read randomness from local device


        use Data::Entropy::RawSource::Local;
        my $rawsrc = Data::Entropy::RawSource::Local->new;
        $rawsrc->sysread($c, 1);
        # and the rest of the I/O handle interface


This class provides a constructor to open an I/O handle connected to a local source of random octets. This may be a strong entropy source, depending on the OS, but not every OS has such a facility at all.

There are no actual objects blessed into this class. Only the constructor belongs to this class; it returns "IO::File" objects. For use as a general entropy source, it is recommended to wrap the handle using "Data::Entropy::Source", which provides methods to extract entropy in more convenient forms than mere octets.

On systems with a blocking /dev/random, such as Linux, the bits generated can be totally unbiased and uncorrelated. Such an entropy stream is suitable for all uses, including security applications. However, the rate of entropy generation is limited, so applications requiring a large amount of apparently-random data might prefer to fake it cryptographically (see Data::Entropy::RawSource::CryptCounter).

On systems where /dev/random does not block, the bits generated are necessarily correlated to some extent, but it should be cryptographically difficult to detect the correlation. Such an entropy source is not suitable for all applications. Some other systems lack /dev/random entirely. If satisfactory entropy cannot be generated locally, consider downloading it from a server (see Data::Entropy::RawSource::RandomOrg and Data::Entropy::RawSource::RandomnumbersInfo).


Opens a file handle referring to the randomness device, or "die"s on error. The device opened is /dev/random by default, but this may be overridden by giving a FILENAME argument.

The default device name may in the future be different on different OSes, if their equivalent devices are in different places.


There are no actual objects blessed into this class. The constuctor returns "IO::File" objects. See IO::File for the interface. It is recommended to use unbuffered reads (the "sysread" method) rather than buffered reads (the "getc" method et al), to avoid wasting entropy that could be used by another process.


Data::Entropy::RawSource::CryptCounter, Data::Entropy::RawSource::RandomOrg, Data::Entropy::RawSource::RandomnumbersInfo, Data::Entropy::Source, IO::File


Andrew Main (Zefram) <>


Copyright (C) 2006, 2007, 2009, 2011 Andrew Main (Zefram) <>


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

2022-06-12 perl v5.34.0