Classical Ciphers, Cryptanalysis & CTF Tools
Two thousand years of pen-and-paper cryptography — and the analysis tools that break it. Built for learning and Capture The Flag.
Caesar Cipher
Shift cipher with instant all-25 bruteforce
VIGENÈRE · POLYVigenère Cipher
The polyalphabetic cipher that resisted breaking for 300 years
ATBASH · AFFINEAtbash & Affine
Mirror-alphabet and modular substitution ciphers
RAIL FENCE · ZIGZAGRail Fence Cipher
Zigzag transposition across configurable rails
BACON · 5-BITBaconian Cipher
Francis Bacon's five-bit steganographic alphabet
POLYBIUS · 5×5Polybius & Tap Code
Coordinate ciphers from ancient Greece to POW camps
ANALYSIS · χ² · ICFrequency Analysis
Letter statistics, index of coincidence, chi-square
ENIGMA · M3Enigma Machine
The WWII cipher machine, with rotors, rings, and plugboard
PLAYFAIR · 5×5Playfair Cipher
The digraph cipher with a 5×5 keyed square
OTP · PADOne-Time Pad
The only provably unbreakable cipher — if used correctly
Choosing the right classical ciphers & ctf tool
Classical ciphers — Caesar, Vigenère, Playfair, Enigma — protected secrets for two thousand years before computers made them trivial to break. Today they're the best way to learn how cryptanalysis works, and staples of puzzle hunts, escape rooms and Capture The Flag competitions.
Start unknown ciphertext with frequency analysis: an index of coincidence near 0.066 points to a substitution or transposition of English, while values near 0.04 suggest a polyalphabetic cipher like Vigenère. Shift ciphers fall instantly to the Caesar bruteforcer; Vigenère yields to Kasiski examination and chi-squared scoring. The one-time pad is the exception — used correctly, it is provably unbreakable.