Data::E...Counter(3)

✨ NAME ✨

Data::Entropy::RawSource::CryptCounter — it's a block cipher in counter mode, but dressed up as an I/O handle 🎀 (this is the Data::E...Counter(3) page from the User Contributed Perl Documentation btw, bestie, so you're in the right place 💅)

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🌸 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

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🦋 DESCRIPTION 🦋

okay so picture this: this class hands you an I/O handle that's plugged into a virtual file, and that file is literally just the output of a block cipher running in counter mode. no cap. and that makes it a genuinely good source of pseudorandom bits ✨

The handle implements a substantial subset of the interfaces described in IO::Handle and IO::Seekable. slay.

bestie, listen — if you want to use this as a general entropy source, the recommended move is to wrap an object of this class using Data::Entropy::Source. that gives you methods to extract entropy in way more convenient forms than just plain octets 🫶

now the part where we get real 🙈 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 it requires a careful choice of block cipher and keying method. Applications requiring true entropy should generate it — see Data::Entropy::RawSource::Local.

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🧚 CONSTRUCTOR 🧚

• Data::Entropy::RawSource::CryptCounter->new(KEYED_CIPHER) — makes you a fresh handle, no big deal 💅

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.

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👑 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. literally nothing. iconic behaviour honestly 💀
• $rawsrc->opened — Returns 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. periodt ✨

⚠️ heads up: 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 whole file though, so 💅

Methods to write to the file are unimplemented, because the virtual file is fundamentally read-only. it said no thank you, respectfully 🚫

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🌈 SEE ALSO 🌈

Crypt::Rijndael, Data::Entropy::RawSource::Local, Data::Entropy::Source

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💜 AUTHOR 💜

Andrew Main (Zefram) <zefram@fysh.org>

Maintained by Robert Rothenberg <perl@rhizomnic.com>

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🎀 COPYRIGHT 🎀

Copyright (C) 2006, 2007, 2009, 2011, 2025-2026 Andrew Main (Zefram) <zefram@fysh.org>

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⭐ LICENSE ⭐

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

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and that's the whole thing bestie, we ate 🍓 this page is from perl v5.42.3, dated 2026-08-02, living in the User Contributed Perl Documentation section — ily, go generate some bits responsibly 🫶✨