RC2

RC2 is a conventional, secret-key block cipher whose input and output blocks are each 64 bits. It is described in RFC 2268, an informational memo from March 1998 by R. Rivest of the MIT Laboratory for Computer Science and RSA Data Security, Inc., which offers it as a possible replacement for DES. The key size is variable, from one byte up to 128 bytes, although the implementation described in the memo uses eight bytes, and the specification also defines an effective key length in bits that caps the search space. The design aims at easy implementation on 16-bit microprocessors; the memo reports that on an IBM AT the encryption runs about twice as fast as DES once key expansion has been done. The algorithm has three parts: a key expansion that turns the supplied key into 64 sixteen-bit words using a table of bytes based on the digits of pi, an encryption routine and its inverse decryption routine.