FFXRadix

A PHP implementation of the FFX[radix] Scheme of The FFX Mode of Operation for Format-Preserving Encryption[1,2]. Also known as mode FF1 in NIST Special Publication 800-38G: Recommendation for Block Cipher Modes of Operation: Methods for Format-Preserving Encryption[3]

Encrypt and decrypt a message with a radix between 2 to 62 and preserves its length. Messages to be enciphered under FFX[radix] are regarded as strings of characters drawn from the alphabet Chars = {0, 1, 2,...,radix − 1}. Scheme FFX[radix] does its work using an AES-based balanced Feistel network. If the message length is odd, an alternating, maximally-balanced Feistel scheme is used instead.

• [1] http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/ffx/ffx-spec.pdf
• [2] http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/ffx/ffx-spec2.pdf
• [3] http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-38G.pdf

Example Usage

<?php
require __DIR__.'/vendor/autoload.php';

use Janv\FFXRadix\FFXRadix;

// Key must be a 16 byte long string if AES-128 (default) is used
$key = hex2bin('00000000000000000000000000000000');
// Tweak can be anything
$tweak = hex2bin('0123456789abcdef');

$ffx = new FFXRadix();

// Encrypt a 16 decimal number (radix = 10)
$enc = $ffx->encrypt(sprintf('%016d', 1), 10, $key, $tweak);
// Outputs 1299047952447293
echo "$enc\n";

// Decrypt
$dec = $ffx->decrypt($enc, 10, $key, $tweak);
// Outputs 0000000000000001
echo "$dec\n";

Testing

This implementation is validated against the test vectors provided in:

• http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/ffx/aes-ffx-vectors.txt
• http://csrc.nist.gov/groups/ST/toolkit/documents/Examples/FF1samples.pdf