Crypt::RC4 is something fast and encrypted strings can be base64encoded to be put into a hidden field. You can then decode the hidden field on every cgi run.

You can sort of hide the key from casual eyes, with some code like:

my $password = pack('C*', (0x01,0x23,0x45,0x67,0x89,0xab,0xcd,0xef));
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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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