This was one of the most secure hand ciphers used in the Second World War. It was used by both the Allies and the Axis, and served both well. Its main weakness was that if the attacker intercepted two ...

A substitution cipher is a cipher that maps each symbol in the plaintext to a symbol according to a permutation of the alphabet. A breakpoint is a location in the ciphertext where the cipher changes.

The keys are correct as stated, but instead of numbering duplicate letters from left to right, Agent Madeleine numbered them from right to left. You may want to complete the decryption yourself before ...