"Rivest, a professor at MIT who worked with Shamir and Len Adleman to design the original RSA algorithm, also said that he still gets email and calls from people wanting to use the MD5 hash function, which he designed in 1991. MD5 was widely used, but has been shown to have several weaknesses in recent years. "I always say to them, 'Don't you understand that MD5 is an extinct hash function? It's dead,'" Rivest said." - Tracy