One-Time Pad

Explanation

A One-Time Pad cipher is a type of encryption technique that provides perfect secrecy when used correctly. The essence of a One-Time Pad cipher lies in the use of a randomly generated key that is at least as long as the message being encrypted.

The key is never reused and is kept completely secret between the sender and the recipient. Each character of the plaintext message is combined with the corresponding bit or character of the key using a the same shift as the Caesar cipher.

In a slightly less secure, but more practical key selection, the passage of a book can also be used. Preferably one with a good mix of many characters that would make frequency analysis more difficult.

When these principles are followed, the One-Time Pad provides perfect secrecy, meaning that the ciphertext reveals no information about the plaintext, even when the attacker has unlimited computational power.

However, achieving and maintaining these conditions in practice can be extremely challenging, which limits the practical use of the One-Time Pad cipher.

Facts

It was invented independently by Gilbert Vernam in 1917 and later rediscovered by Joseph Mauborgne and patented by both in 1919.

It was used by espionage agencies during the cold war, notably the Soviet spy network Venona Project used it to communicate securely.