The original suggested choice of parameters were a block size of 64 bits, a 128-bit key, and 12 rounds.

A key feature of RC5 is the use of data-dependent rotations; one of the goals of RC5 was to prompt the study and evaluation of such operations as a cryptographic primitive.

[citation needed] RC5 also consists of a number of modular additions and eXclusive OR (XOR)s. The general structure of the algorithm is a Feistel-like network, similar to RC2.

The tantalising simplicity of the algorithm together with the novelty of the data-dependent rotations has made RC5 an attractive object of study for cryptanalysts.

[3] The key expansion algorithm is illustrated below, first in pseudocode, then example C code copied directly from the reference paper's appendix.

[6] RSA Security, which had a (now expired) patent on the algorithm,[7] offered a series of US$10,000 prizes for breaking ciphertexts encrypted with RC5, but these contests were discontinued as of May 2007.