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A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream . 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 ciphertext stream.
The table below shows the support of various stream ciphers. Stream ciphers are defined as using plain text digits that are combined with a pseudorandom cipher digit stream. Stream ciphers are typically faster than block ciphers and may have lower hardware complexity, but may be more susceptible to attacks.
Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. In the broadest sense, it is the study of how differences in information input can affect the resultant difference at the output.
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: E(A) = A xor C
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.
Although ciphers can be confusion-only (substitution cipher, one-time pad) or diffusion-only (transposition cipher), any "reasonable" block cipher uses both confusion and diffusion. [2] These concepts are also important in the design of cryptographic hash functions , and pseudorandom number generators , where decorrelation of the generated ...
Informally, a block cipher is secure in the standard model if an attacker cannot tell the difference between the block cipher (equipped with a random key) and a random permutation. To be a bit more precise, let E be an n-bit block cipher. We imagine the following game: The person running the game flips a coin.
Block ciphers operate on a fixed length string of bits. The length of this bit string is the block size . [ 1 ] Both the input ( plaintext ) and output ( ciphertext ) are the same length; the output cannot be shorter than the input – this follows logically from the pigeonhole principle and the fact that the cipher must be reversible – and ...