In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a single-use pre-shared key that is larger than or equal to the size of the message being sent. In this technique, a plaintext is paired with a random secret key (also referred to as a one-time pad). Then, each bit or character of the plaintext is encrypted by combining it with the corresponding bit or character from the pad using modular addition.[1]

The resulting ciphertext will be impossible to decrypt or break if the following four conditions are met:[2][3]

1. The key must be at least as long as the plaintext.

2. The key must be truly random.

3. The key must never be reused in whole or in part.

4. The key must be kept completely secret by the communicating parties.

It has also been mathematically proven that any cipher with the property of perfect secrecy must use keys with effectively the same requirements as OTP keys.[4] Digital versions of one-time pad ciphers have been used by nations for critical diplomatic and military communication, but the problems of secure key distribution make them impractical for most applications.

References:

1. Lugrin, Thomas (2023), Mulder, Valentin; Mermoud, Alain; Lenders, Vincent; Tellenbach, Bernhard (eds.), "One-Time Pad", Trends in Data Protection and Encryption Technologies, Cham: Springer Nature Switzerland, pp. 3–6, doi:10.1007/978-3-031-33386-6_1, ISBN 978-3-031-33386-6

2. ^ Jump up to:^{a b c d} "Intro to Numbers Stations". Archived from the originalon 18 October 2014. Retrieved 13 September 2014.

3. ^ "One-Time Pad (OTP)". Cryptomuseum.com. Archived from the original on 2014-03-14. Retrieved 2014-03-17.

4. ^ Jump up to:^{a b} Shannon, Claude (1949). "Communication Theory of Secrecy Systems" (PDF). Bell System Technical Journal. 28 (4): 656–715. doi:10.1002/j.1538-7305.1949.tb00928.x.