From: http://practicalcryptography.com/ciphers/classical-era/baconian/

The Baconian cipher is named after its inventor, Sir Francis Bacon. The Baconian cipher is a substitution cipher in which each letter is replaced by a sequence of 5 characters. In the original cipher, these were sequences of 'A's and 'B's e.g. the letter 'D' was replaced by 'aaabb', the letter 'O' was replaced by 'abbab' etc.

Each letter is assigned to a string of five binary digits. These could be the letters 'A' and 'B', the numbers 0 and 1 or whatever else you may desire. An example Baconian Cipher Encoding might be:

A = aaaaa  I/J = abaaa    R = baaaa
B = aaaab    K = abaab    S = baaab
C = aaaba    L = ababa    T = baaba
D = aaabb    M = ababb  U/V = baabb
E = aabaa    N = abbaa    W = babaa
F = aabab    O = abbab    X = babab
G = aabba    P = abbba    Y = babba
H = aabbb    Q = abbbb    Z = babbb

To encipher a message, e.g. 'STRIKE NOW', we replace each letter:

S     T     R     I     K     E     N     O     W 
baaab baaba baaaa abaaa abaab aabaa abbaa abbab babaa

Use the above to create a command line program that encodes a baconian cipher.

Dynamically generate the letter subsitutions

Take an argument to change the number of letters in the generated subsitution

Take an argument for which two letters that are in the subsitution

Take an argument for how many different letters are used in the subsitution