The Cipher Challenge Contest
Four degrees of difficulty, from pen & paper to complex mathematical problems
Solved Level 1 challenge Turing Bombe Enigma I
Solved Level 1 challenge Enigma Combinatorics
Solved Level 1 challenge Enigma Messages with Repeated Letters — Part 3
Solved Level 1 challenge Enigma Messages with Repeated Letters — Part 2
Solved Level 1 challenge Enigma Messages with Repeated Letters — Part 1
Solved Level 1 challenge Playfair with hints about the grid
Solved Level 1 challenge Playfair Encryption
Solved Level 2 challenge Flawed Usage of a OTP Cipher by the BND
Four degrees of difficulty, from pen & paper to complex mathematical problems