Block Ciphers

A block cipher is a family of permutations. Block cipher design is composed of defining a good round function, repeating it a sufficient number of times to offer adequate security margins, as long as the performance is acceptable. This chapter discusses the recent emerging need for special environment ciphers: secure multiparty computation protocols or as part of succinct non-interactive argument of knowledge. Most block ciphers fall under the definition of general purpose block ciphers. There are two common structures for block ciphers. The first is the Feistel block cipher, which was adopted by the designers of the data encryption standard. The second common structure of the block cipher is substitution permutation networks (SPNs). Decryption of SPNs is actually done by calling the inverse operations. Most block ciphers employ a key schedule algorithm, which expands the key into subkeys.