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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).
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]
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.
Keystreams are used in the one-time pad cipher and in most stream ciphers. Block ciphers can also be used to produce keystreams. For instance, CTR mode is a block mode that makes a block cipher produce a keystream and thus turns the block cipher into a stream cipher.
ISAAC (indirection, shift, accumulate, add, and count) is a cryptographically secure pseudorandom number generator and a stream cipher designed by Robert J. Jenkins Jr. in 1993. [1] The reference implementation source code was dedicated to the public domain. [2] "I developed (...) tests to break a generator, and I developed the generator to ...
One round (out of 8.5) of the IDEA cipher, used in most versions of PGP and OpenPGP compatible software for time-efficient encryption of messages. Symmetric key ciphers are implemented as either block ciphers or stream ciphers. A block cipher enciphers input in blocks of plaintext as opposed to individual characters, the input form used by a ...
In the asymptotic setting, a family of deterministic polynomial time computable functions : {,} {,} for some polynomial p, is a pseudorandom number generator (PRNG, or PRG in some references), if it stretches the length of its input (() > for any k), and if its output is computationally indistinguishable from true randomness, i.e. for any probabilistic polynomial time algorithm A, which ...
In hash-based cryptography, the Merkle signature scheme is a digital signature scheme based on Merkle trees (also called hash trees) and one-time signatures such as the Lamport signature scheme. It was developed by Ralph Merkle in the late 1970s [1] and is an alternative to traditional digital signatures such as the Digital Signature Algorithm ...