erlffx

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 / 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
• The number of rounds is configurable (10 by default)

The unit tests were written using the following lists of test vectors:

• AES FFX Test Vector Data
• FF1 samples

Examples

% 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