# Tag Info

## New answers tagged des

1

General descryption The block cipher is an operation that lives in the box [block cipher encryption]. A block cipher can do two things: encrypt and decrypt. It is parametrized by a key, which is one of two inputs. The other input is a block of data. The output is the keyed permutation of that block of data. A permutation is a 1:1 relation; each input block ...

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DES would be the box in your diagram that's labeled "Block Cipher Encryption", and it participates in the encryption mode you show in two ways: the output is XORed with the plaintext, and the output is used as the input to the next block's use of DES (the second "Block Cipher Encryption"). In this mode, you're using DES to generate a sequence of random ...

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As DES doesn't have a random number generator as input (or anything else to draw entropy from), it cannot perform anything at random. DES itself is fully deterministic, i.e. for identical key and block of plaintext, it will always create an identical block of ciphertext. Fully deterministic doesn't mean that it cannot lose information or contain ...

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Formally, a block cipher is a family of permutations, indexed by the key. More specifically, let $P$ be the set of all permutations (shufflings of elements as you put it) on the set of $n$ bit strings, i.e. the Symmetric Group $Sym(\{0,1\}^n)$. The $n$-bit block cipher $B$ is a subset of $P$. The key specifies which element of the subset $B$ is to be used ...

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You run the algorithm with two different plaintexts (whose difference is usually small, just a few bits, everything else being equal). Whereever these plaintexts lead to different inputs to an S-box (in any layer/round of the algorithm), we call this S-Box active (since the other S-boxes produce the same result for both plaintexts, they are called "passive" ...

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