Contents

= affine

An affine cipher is a monoalphabetic substitution cipher, that uses
math to generate the substitution alphabet based on three paramaters:

[modulus] specifies how many different plaintexts and ciphertexts
          are available.
[a_key] multiplied against the plaintext. <b>Must be coprime with
        the modulus.</b>
[b_key] added to the multiplied plaintext.  No restrictions, but
        it's modulus math, so making it larger than +modulus+ is
        useless.

These parameters are passed in order to the Cipher constructor:

    a = Affine::Cipher.new(2176782371, 65182241782, 123235151)
    r = rand(123235150) # (should be smaller then the modulus)
    ciphertext = a.encipher r
    # ciphertext = ((r * 65182241782) + 123235151) % 2176782371
    r == a.decipher(ciphertext)

== Giant security caveat

Don't use this cipher for security related tasks.  I'm using it
to make primary keys alphanumeric and less-predictable:
http://github.com/bkerley/have-code/

== How to crack it

Know two plaintexts and their ciphertexts, put into linear system, solve.

Know the relation between two plaintexts, predict future ciphertexts.

Know lots of ciphertexts, guess it's English, solve like a cryptogram.

== Copyright

Copyright (c) 2009 Bryce Kerley. See LICENSE for details.

Version data entries

4 entries across 4 versions & 2 rubygems

Version	Path
bkerley-affine-0.2.2	README.rdoc
bkerley-affine-0.2.3	README.rdoc
affine-0.2.3	README.rdoc
affine-0.2.2	README.rdoc