SKILL: Classical Cipher Analysis — Expert Cryptanalysis Playbook

AI LOAD INSTRUCTION: Expert classical cipher identification and breaking techniques for CTF. Covers cipher identification methodology (frequency analysis, IC, Kasiski), monoalphabetic substitution, Caesar/ROT, Vigenere, Enigma, affine, Hill, transposition ciphers, Bacon/Polybius/Playfair, and XOR ciphers. Base models often skip the identification step and jump to the wrong cipher type, or fail to recognize encoded (base64/hex) ciphertext that needs decoding before analysis.

0. RELATED ROUTING

• symmetric-cipher-attacks when dealing with modern symmetric ciphers (AES/DES) rather than classical
• hash-attack-techniques when the challenge involves hash-based constructions
• lattice-crypto-attacks when knapsack-based ciphers are encountered

Quick identification guide

| Observation | Likely Cipher | First Action | |