Symmetric ciphers - continued

• Symmetric ciphers can be subdivided into:

• Block ciphers - Operate on chunks of data (64 bits in DES, 128 in AES). This kind transform is known as a pseudo-random function, and is in general unvaryingly applied to each block.

• Stream ciphers which operate on data either one bit or byte at a time (the rc4 cipher, and A5/1 used in encrypting GSM communications are stream cyphers). The transformation of successive bytes varies based on the current state.