erlffx

Version: 1.1.0

Authors: Guilherme Andrade (erlffx(at)gandrade(dot)net).

erlffx: Format Preserving Encryption - FFX for Erlang

erlffx is an Erlang implementation of the mechanism described in the 2010 paper The FFX Mode of Operation for Format-Preserving Encryption by Bellare, Rogaway and Spies. It is based on an existing Java implementation by Michael Tandy.

AES-128 / AES-192 (only Erlang 19 and up) / AES-256 keys are supported (CBC mode)
Any positive word length is supported
Any radix / alphabet size between 2 and 255 is acceptable (10 by default)
Optional ‘tweak’ values may be defined
Number of rounds is configurable (10 by default)

The code was successfully tested on generations 17, 18 and 19 of Erlang/OTP; the unit tests themselves were written using the following lists of test vectors:

<a name=”Examples”>Examples</a>


% AES-128 CBC / 10-digit decimal words
AesKey = <<43,126,21,22,40,174,210,166,171,247,21,136,9,207,79,60>>,
ValueLength = 10,
Config = erlffx:config(AesKey, ValueLength).

Encrypted = erlffx:encrypt(Config, 123456789). % 2433477484
Decrypted = erlffx:decrypt(Config, Encrypted). % 123456789


% AES-128 CBC / 10-digit decimal words / custom tweak
AesKey = <<43,126,21,22,40,174,210,166,171,247,21,136,9,207,79,60>>,
ValueLength = 10,
Config = erlffx:config(AesKey, ValueLength, #{ tweak => "9876543210" }).

Encrypted = erlffx:encrypt(Config, 123456789). % 6124200773
Decrypted = erlffx:decrypt(Config, Encrypted). % 123456789


% AES-128 CBC / 16-digit base-36 words / custom tweak
AesKey = <<43,126,21,22,40,174,210,166,171,247,21,136,9,207,79,60>>,
ValueLength = 16,
Config = erlffx:config(AesKey, ValueLength, #{ tweak => "TQF9J5QDAGSCSPB1", radix => 36 }).

Encrypted = erlffx:encrypt(Config, 36#C4XPWULBM3M863JH). % 36#C8AQ3U846ZWH6QZP
Decrypted = erlffx:decrypt(Config, Encrypted).           % 36#C4XPWULBM3M863JH


% AES-256 CBC / 6-digit binary words
AesKey = <<43,126,21,22,40,174,210,166,171,247,21,136,9,207,79,60,
           239,67,89,216,213,128,170,79,127,3,109,111,4,252,106,148>>,
ValueLength = 6,
Config = erlffx:config(AesKey, ValueLength, #{ radix => 2 }).

Encrypted = erlffx:encrypt(Config, 2#000001).  % 2#100100
Decrypted = erlffx:decrypt(Config, Encrypted). % 2#000001

Modules

erlffx