hasemcave.blogg.se

1. #Des blocs software
2. #Des blocs professional

The non-linear substitution stage mixes the key bits with those of the plaintext, creating Shannon's confusion. One important type of iterated block cipher known as a substitution–permutation network (SPN) takes a block of the plaintext and the key as inputs, and applies several alternating rounds consisting of a substitution stage followed by a permutation stage-to produce each block of ciphertext output. Main article: Substitution–permutation network Finally, the cipher should be easily cryptanalyzable, such that it can be shown how many rounds the cipher needs to be reduced to, so that the existing cryptographic attacks would work – and, conversely, that it can be shown that the number of actual rounds is large enough to protect against them.

#Des blocs software

In addition, the cipher should be concise, for small hardware and software implementations.

Further, a good block cipher is designed to avoid side-channel attacks, such as branch prediction and input-dependent memory accesses that might leak secret data via the cache state or the execution time.

#Des blocs professional

Thus, efficiency is the most important additional design criterion for professional ciphers. However, this will make the cipher inefficient. Given one of the standard iterated block cipher design schemes, it is fairly easy to construct a block cipher that is cryptographically secure, simply by using a large number of rounds. More formally, a block cipher is specified by an encryption functionĮ K ( P ) := E ( K, P ) : The decryption algorithm D is defined to be the inverse function of encryption, i.e., D = E −1. Both algorithms accept two inputs: an input block of size n bits and a key of size k bits and both yield an n-bit output block.