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.