RC5

The RSA RC5 cipher was the focus of several distributed keyspace exhaustion challenges (notably the distributed.net RC5-56, RC5-64 and RC5-72 efforts) that rallied worldwide volunteer computing in the late 1990s and early 2000s.

• RC5 is a parameterized block cipher (variable block size, key size and number of rounds) designed by Ron Rivest.
• The distributed.net projects demonstrated the practical limits of brute force over time and hardware generations.
• Completion of RC5-64 (2002) and ongoing attempts at RC5-72 highlighted exponential growth in required compute.

• distributed.net