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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]
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 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]
Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. ... apart from the one-time pad, ... for example, the amount ...
If the keystream is truly random and used only once, this is effectively a one-time pad. Substituting pseudorandom data generated by a cryptographically secure pseudo-random number generator is a common and effective construction for a stream cipher. RC4 is an example of a Vernam cipher that is widely used on the Internet.