Breaking Playfair
Single letters look flat here by design. So count letter pairs instead, because pairs are what this cipher encrypts.
CryptanalysisDigraph frequencydemo
Objectives
Rank ciphertext digraphs and compare them with the English table.
Name the structure Playfair leaves in its output beyond digraph frequency.
Explain why moving from 26 symbols to 676 buys text, not security.