A series of encryption algorithms published by RSA Security; all developed by cryptography pioneer Ron Rivest. (Rivest Cipher 2, or Ron’s Code 2 = RC2) All of them are important commercial implementations of symmetric key cryptography where the entity that encrypts and the entity that decrypts both must know the same key.

RC2 was developed as a replacement for DES (Data Encryption Standard) and has been in widespread use in a number of commercial software packages, for SSL and S/MIME implementations, and others. It has had an historical advantage over its competitor, DES, in that, until the laws were liberalized in 2000, along with RC4, it had special export status. In order to be exported a relatively short key length, a weak implementation of 40 bits had to be used. E-mail and web browser interoperability across country borders was a driving factor.

RC5 is a fast and flexible block cipher. The block size, key length and the number of interations are all variable.