Triple DES is an example of a Block Cipher encryption algorithm. Block Ciphers operate on one block of data at a time with the normal block size being set to 64bits. In the case of 3DES, the DES encryption algorithm is applied three times to each 64bit block. This can be achieved using two cipher keys of length 56bits (K1 and K2) applied in the sequence K1 – K2 – K1. Alternatively, three 56bit keys can be used (K1, K2 and K3) applied in the sequence K1 – K2 – K3.