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Crypt::CAST5_PP - CAST5 block cipher in pure Perl


    use Crypt::CBC;

    my $crypt = Crypt::CBC->new({
        key    => "secret key",
        cipher => "CAST5_PP",

    my $message = "All mimsy were the borogoves";
    my $ciphertext = $crypt->encrypt($message);
    print unpack("H*", $ciphertext), "\n";

    my $plaintext = $crypt->decrypt($ciphertext);
    print $plaintext, "\n";


This module provides a pure Perl implementation of the CAST5 block cipher. CAST5 is also known as CAST-128. It is a product of the CAST design procedure developed by C. Adams and S. Tavares.

The CAST5 cipher is available royalty-free.



Returns the CAST5 block size, which is 8 bytes. This function exists so that Crypt::CAST5_PP can work with Crypt::CBC.


Returns the maximum CAST5 key size, 16 bytes.


    $cast5 = Crypt::CAST5_PP->new($key);

Create a new encryption object. If the optional key parameter is given, it will be passed to the init() function.



Set or change the encryption key to be used. The key must be from 40 bits (5 bytes) to 128 bits (16 bytes) in length. Note that if the key used is 80 bits or less, encryption and decryption will be somewhat faster.

It is best for the key to be random binary data, not something printable like a password. A message digest function may be useful for converting a password to an encryption key; see Digest::SHA1 or Digest::MD5. Note that Crypt::CBC runs the given "key" through MD5 to get the actual encryption key.


    $ciphertext = $cast5->encrypt($plaintext);

Encrypt a block of plaintext using the current encryption key, and return the corresponding ciphertext. The input must be 8 bytes long, and the output has the same length. Note that the encryption is in ECB mode, which means that it encrypts each block independently. That can leave you vulnerable to dictionary attacks, so it is generally best to use some form of chaining between blocks; see Crypt::CBC.


    $plaintext = $cast5->decrypt($ciphertext);

Decrypt the ciphertext and return the corresponding plaintext.


Always produces untainted output, even if the input is tainted, because that's what perl's pack() function does.


RFC 2144, "The CAST-128 Encryption Algorithm", C. Adams, May 1997



Bob Mathews, <>


Copyright (c) 2006 Bob Mathews. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.