If you need it for cgi on a remote server, I would suggest
the Crypt::RC4 module from cpan. It is pure perl so you can
upload it to your server and use it.
This also uses MIME::Base64 to make your data printable
for sending over the net.
If you need to upload the RC4.pm to your server, you need to
make a few changes.

BEGIN{unshift(@INC,'/home/yourusername/public_html/cgi-bin')}
use RC4;
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#!/usr/bin/perl
use strict;
use warnings;
use Crypt::RC4;
use MIME::Base64;
my $key       = "abcdefghijklm";
my $plaintext = "Hello, World!";
my $encrypted = RC4($key, $plaintext);

my $encoded = encode_base64($encrypted);
my $decoded = decode_base64($encoded);
print "$encoded\n";
print "$decoded\n";

my $decrypted = RC4($key, $decoded);
print "$decrypted\n";
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