In cryptography, 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 corresponding digit of the keystream, to give a digit of the cyphertext stream. An alternative name is a state cipher, as the encryption of each digit is dependent on the current state. In practice, a digit is typically a bit and the combining operation an exclusive-or (xor).
The pseudorandom keystream is typically generated serially from a random seed value using digital shift registers. The seed value serves as the cryptographic key for decrypting the ciphertext stream.
Stream ciphers represent a different approach to symmetric encryption from block ciphers. Block ciphers operate on large blocks of digits with a fixed, unvarying transformation. This distinction is not always clear-cut: in some modes of operation, a block cipher primitive is used in such a way that it acts effectively as a stream cipher. Stream ciphers typically execute at a higher speed than block ciphers and have lower hardware complexity. However, stream ciphers can be susceptible to serious security problems if used incorrectly (see stream cipher attacks); in particular, the same starting state (seed) must never be used twice.
Read more about Stream Cipher: Loose Inspiration From The One-time Pad, Types of Stream Ciphers, Linear Feedback Shift Register-based Stream Ciphers, Other Designs, Security, Usage, Comparison of Stream Ciphers, Trivia
Other articles related to "ciphers, stream cipher, stream, cipher":
... The BEAR and LION block ciphers were invented by Ross Anderson and Eli Biham by combining a stream cipher and a cryptographic hash function ... Both are 3 round generalized Feistel ciphers, using the hash function and the stream cipher as round functions ... LION uses the stream cipher twice and the hash function once ...
... which can be used both as a hash function and a stream cipher ... Daemen and Craig Clapp and presented in the paper Fast Hashing and Stream Encryption with PANAMA on the Fast Software Encryption (FSE) conference 1998 ... The cipher has influenced several other designs, for example MUGI ...
... United States National Security Agency documents sometimes use the term combiner-type algorithms, referring to algorithms that use some function to combine a pseudorandom number generator (PRNG) with a plaintext stream. ...
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