Classical Cipher Analysis

This is a CTF-focused playbook that walks you through identifying and breaking classical ciphers. It starts with character set analysis to distinguish between base64, hex, Morse, or actual cipher text, then uses frequency analysis and index of coincidence to figure out if you're dealing with monoalphabetic substitution, Caesar, Vigenere, or something else. The code samples are practical: Kasiski examination for finding Vigenere key lengths, chi-squared scoring for Caesar brute force, and crib dragging when you have known plaintext. The identification table up front is genuinely useful because the skill explicitly calls out that base models tend to skip the detection step and jump straight to the wrong cipher type. Routes you to symmetric cipher attacks if it turns out to be AES instead of ROT13.