The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


Crypt::RC4 - Perl implementation of the RC4 encryption algorithm


# Functional Style use Crypt::RC4; $encrypted = RC4( $passphrase, $plaintext ); $decrypt = RC4( $passphrase, $encrypted );

# OO Style use Crypt::RC4; $ref = Crypt::RC4->new( $passphrase ); $encrypted = $ref->RC4( $plaintext );

  $ref2 = Crypt::RC4->new( $passphrase );
  $decrypted = $ref2->RC4( $encrypted );

# process an entire file, one line at a time # (Warning: Encrypted file leaks line lengths.) $ref3 = Crypt::RC4->new( $passphrase ); while (<FILE>) { chomp; print $ref3->RC4($_), "\n"; }


A simple implementation of the RC4 algorithm, developed by RSA Security, Inc. Here is the description from RSA's website:

RC4 is a stream cipher designed by Rivest for RSA Data Security (now RSA Security). It is a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. Analysis shows that the period of the cipher is overwhelmingly likely to be greater than 10100. Eight to sixteen machine operations are required per output byte, and the cipher can be expected to run very quickly in software. Independent analysts have scrutinized the algorithm and it is considered secure.

Based substantially on the "RC4 in 3 lines of perl" found at

A major bug in v1.0 was fixed by David Hook ( Thanks, David.


Kurt Kincaid ( Ronald Rivest for RSA Security, Inc.


Disclaimer: Strictly speaking, this module uses the "alleged" RC4 algorithm. The Algorithm known as "RC4" is a trademark of RSA Security Inc., and this document makes no claims one way or another that this is the correct algorithm, and further, make no claims about the quality of the source code nor any licensing requirements for commercial use.

There's nothing preventing you from using this module in an insecure way which leaks information. For example, encrypting multilple messages with the same passphrase may allow an attacker to decode all of them with little effort, even though they'll appear to be secured. If serious crypto is your goal, be careful. Be very careful.

It's a pure-Perl implementation, so that rating of "Eight to sixteen machine operations" is good for nothing but a good laugh. If encryption and decryption are a bottleneck for you, please re-write this module to use native code wherever practical.


This is free software and may be modified and/or redistributed under the same terms as Perl itself.