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Keystream. In cryptography, a keystream is a stream of random or pseudorandom characters that are combined with a plaintext message to produce an encrypted message (the ciphertext). The "characters" in the keystream can be bits, bytes, numbers or actual characters like A-Z depending on the usage case. Usually each character in the keystream is ...
Stream cipher. The operation of the keystream generator in A5/1, an LFSR-based stream cipher used to encrypt mobile phone conversations. A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream ( keystream ). In a stream cipher, each plaintext digit is encrypted one at a time with the ...
The keystream generated by the RC4 is biased to varying degrees towards certain sequences, making it vulnerable to distinguishing attacks. The best such attack is due to Itsik Mantin and Adi Shamir, who showed that the second output byte of the cipher was biased toward zero with probability 1/128 (instead of 1/256). This is due to the fact that ...
Stream ciphers are vulnerable to attack if the same key is used twice (depth of two) or more. Say we send messages A and B of the same length, both encrypted using same key, K. The stream cipher produces a string of bits C (K) the same length as the messages. The encrypted versions of the messages then are: where xor is performed bit by bit.
When the keystream is generated by a pseudo-random number generator, the result is a stream cipher. With a key that is truly random, the result is a one-time pad, which is unbreakable in theory. The XOR operator in any of these ciphers is vulnerable to a known-plaintext attack, since plaintext ciphertext = key. It is also trivial to flip ...
A nonce is an arbitrary number used only once in a cryptographic communication, in the spirit of a nonce word. They are often random or pseudo-random numbers. Many nonces also include a timestamp to ensure exact timeliness, though this requires clock synchronisation between organisations. The addition of a client nonce (" cnonce ") helps to ...
Running key cipher. In classical cryptography, the running key cipher is a type of polyalphabetic substitution cipher in which a text, typically from a book, is used to provide a very long keystream. The earliest description of such a cipher was given in 1892 by French mathematician Arthur Joseph Hermann (better known for founding Éditions ...
FIREFLY key - (NSA) keys used in an NSA system based on public key cryptography. key encryption key (KEK) - key used to protect MEK keys (or DEK/TEK if MEK is not used). key production key (KPK) -Key used to initialize a keystream generator for the production of other electronically generated keys.