Some ciphers have simple keys, others, complex ones. The key for a cipher used by Augustus Caesar, some 2,000 years ago, was simple enough: The receiver just had to shift the alphabet one position.

The Double Transposition Cipher Back to Crack the Ciphers 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.

The Playfair cipher is an incredibLe code system that is both difficult to decrypt without a computer and easily solvable by hand. Here's how to solve it.

The solution to a Zodiac Killer cipher, unsolved for 51 years, was cracked by a team of codebreakers, the FBI confirmed.