RSA is a public-key cryptosystem named after Ron Rivest, Adi Shamir and Leonard Adleman who invented it at MIT. In using RSA, a user publishes a "public key" that is the product of two large primes. A secret "private key" is held by all parties to the message. RSA is used in a wide variety of internet applications and is currently in the public domain. There are a variety of attacks on RSA-encrypted systems, however they are all hindered by the mathematical difficulty of factoring large primes. Most methods of determining prime factorization of large numbers are essentially brute force.