NAME

       Data::Entropy::RawSource::CryptCounter - counter mode of block cipher as I/O handle

SYNOPSIS

               use Data::Entropy::RawSource::CryptCounter;

               my $rawsrc = Data::Entropy::RawSource::CryptCounter
                               ->new(Crypt::Rijndael->new($key));

               $c = $rawsrc->getc;
               # and the rest of the I/O handle interface

DESCRIPTION

       This class provides an I/O handle connected to a virtual file which contains the output of
       a block cipher in counter mode.  This makes a good source of pseudorandom bits.  The
       handle implements a substantial subset of the interfaces described in IO::Handle and
       IO::Seekable.

       For use as a general entropy source, it is recommended to wrap an object of this class
       using "Data::Entropy::Source", which provides methods to extract entropy in more
       convenient forms than mere octets.

       The amount of entropy the virtual file actually contains is only the amount that is in the
       key, which is at most the length of the key.  It superficially appears to be much more
       than this, if (and to the extent that) the block cipher is secure.  This technique is not
       suitable for all problems, and requires a careful choice of block cipher and keying
       method.  Applications requiring true entropy should generate it (see
       Data::Entropy::RawSource::Local) or download it (see
       Data::Entropy::RawSource::RandomnumbersInfo and Data::Entropy::RawSource::RandomOrg).

CONSTRUCTOR

       Data::Entropy::RawSource::CryptCounter->new(KEYED_CIPHER)
           KEYED_CIPHER must be a cipher object supporting the standard "blocksize" and "encrypt"
           methods.  For example, an instance of "Crypt::Rijndael" (with the default "MODE_ECB")
           would be appropriate.  A handle object is created and returned which refers to a
           virtual file containing the output of the cipher's counter mode.

METHODS

       A subset of the interfaces described in IO::Handle and IO::Seekable are provided:

       $rawsrc->read(BUFFER, LENGTH[, OFFSET])
       $rawsrc->getc
       $rawsrc->ungetc(ORD)
       $rawsrc->eof
           Buffered reading from the source, as in IO::Handle.

       $rawsrc->sysread(BUFFER, LENGTH[, OFFSET])
           Unbuffered reading from the source, as in IO::Handle.

       $rawsrc->close
           Does nothing.

       $rawsrc->opened
           Retruns true to indicate that the source is available for I/O.

       $rawsrc->clearerr
       $rawsrc->error
           Error handling, as in IO::Handle.

       $rawsrc->getpos
       $rawsrc->setpos(POS)
       $rawsrc->tell
       $rawsrc->seek(POS, WHENCE)
           Move around within the buffered source, as in IO::Seekable.

       $rawsrc->sysseek(POS, WHENCE)
           Move around within the unbuffered source, as in IO::Seekable.

       The buffered ("read" et al) and unbuffered ("sysread" et al) sets of methods are
       interchangeable, because no such distinction is made by this class.

       "tell", "seek", and "sysseek" only work within the first 4 GiB of the virtual file.  The
       file is actually much larger than that: for Rijndael (AES), or any other cipher with a
       128-bit block, the file is 2^52 YiB (2^132 B).  "getpos" and "setpos" work throughout the
       file.

       Methods to write to the file are unimplemented because the virtual file is fundamentally
       read-only.

SEE ALSO

       Crypt::Rijndael, Data::Entropy::RawSource::Local, Data::Entropy::RawSource::RandomOrg,
       Data::Entropy::RawSource::RandomnumbersInfo, 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.