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The accepted answer is completely wrong. There is a simple way to convert a stream cipher into a block cipher. In pact, it works for any PRF, regardless of if it is reversible or not. This presentation perfectly covers how to use a PRG such as a stream cipher to construct a block cipher. Basically, you use the stream cipher in the following manner: Take ...


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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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