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Secure generation and exchange of the one-time pad values, which must be at least as long as the message. This is important because the security of the one-time pad depends on the security of the one-time pad exchange. If an attacker is able to intercept the one-time pad value, they can decrypt messages sent using the one-time pad. [18]
To decrypt the output, merely reapplying the XOR function with the key will remove the cipher. ... the result is a one-time pad, ... (for example, AND would produce ...
Stream ciphers can be viewed as approximating the action of a proven unbreakable cipher, the one-time pad (OTP). A one-time pad uses a keystream of completely random digits. The keystream is combined with the plaintext digits one at a time to form the ciphertext. This system was proven to be secure by Claude E. Shannon in 1949. [1]
The following attack on a one-time pad allows full recovery of the secret key. Suppose the message length and key length are equal to n. The adversary sends a string consisting of n zeroes to the oracle. The oracle returns the bitwise exclusive-or of the key with the string of zeroes.
A Vigenère cipher with a completely random (and non-reusable) key which is as long as the message becomes a one-time pad, a theoretically unbreakable cipher. [15] Gilbert Vernam tried to repair the broken cipher (creating the Vernam–Vigenère cipher in 1918), but the technology he used was so cumbersome as to be impracticable. [16]
To decrypt, the process is reversed. Unlike the otherwise very similar Vigenère cipher, the Beaufort cipher is a reciprocal cipher, that is, decryption and encryption algorithms are the same. This obviously reduces errors in handling the table which makes it useful for encrypting larger volumes of messages by hand, for example in the manual ...
The one-time pad is, in most cases, impractical as it requires that the key material be as long as the plaintext, actually random, used once and only once, and kept entirely secret from all except the sender and intended receiver. When these conditions are violated, even marginally, the one-time pad is no longer unbreakable.
A worked example of a one-time pad is needed, showing how two different pads can be used to decrypt a ciphertext into contradictory plaintexts. The history of the invention of the one-time pad An explanation of why, when hearing that a piece of encryption software uses a "one-time pad", most cryptographers burst into peals of hysterical ...