How do you break the playfair cipher?

Answer 1

The Playfair is susceptible to digraph frequency analysis. Separate the plaintext into digraphs and do a frequency count. Once you've found that, compare the digraph frequency of the ciphertext to the digraph frequency of English and see how it might fit in to the Playfair grid. An intimate understanding of how letters in the grid relate to each other and implications of how the grid is affected by correspondences between the ciphertext and plaintext is critical. I'll try to post a help video on YouTube in the near future.