## Playfair

This bigram cipher is a bit trickier...

This cipher text was encrypted using the Playfair cipher.

Since similar keys result in similar ciphertexts for a given plaintext, the playfair cipher is susceptible to optimization algorithms. Start with a random key or several random keys, and optimize until the decrypted ciphertext appears to be English. Some useful algorithms are Simulated Annealing and Genetic Algorithms. The plaintext describes how to submit the solution.

#### Test Vector

Using the pass phrase TESTING results in the key
TESIN
GABCD
FHKLM
OPQRU
VWXYZ

The message hello world is preprocessed to HELXOWORLD. Notice that the second 'L' was converted to an 'X'. This plain text is encrypted to PAKYPVPUMC.