Cracking Playfair Ciphers (2023)
15 hours ago
- #Playfair-cipher
- #code-breaking
- #cryptography
- The Zodiac 340 cipher was cracked in 2020 after 50 years, revealing a homophonic substitution cipher with encoding errors.
- Substitution ciphers are considered weak, with homophonic variants offering little additional security.
- The Playfair cipher, used in WWI, is more secure than substitution ciphers and can be encoded/decoded by hand.
- Playfair cipher uses a 5x5 grid of letters (I and J merged), with encryption based on digraphs (letter pairs).
- Encryption rules include rectangle corner swaps, same row/column shifts, and handling duplicate letters with 'Z' or 'X'.
- Playfair's security comes from mixing digraphs non-linearly, similar to modern block ciphers like AES.
- Known plaintext attacks on Playfair involve analyzing ciphertext patterns to deduce the key.
- Simulated annealing and parallel processing are effective methods for cracking Playfair ciphers, though time-consuming.
- Hyperparameter optimization can improve cracking efficiency, but Playfair remains weak against modern computational methods.
- ChatGPT can assist in deciphering and formatting recovered plaintext, though it's too slow for the cracking process itself.