Semi-ADFGX 18+

grodno_new_year_2026

Task: Modified ADFGX cipher using a 5x6 Polybius square with bigram-encoded ciphertext and a large known-plaintext corpus (Hemingway's "A Farewell to Arms"). Solution: Performed bigram frequency analysis on the known plaintext to build the complete substitution mapping, identifying RW as space (~18.6% frequency), then decrypted and converted spaces to underscores for the flag.