The RSA Encryption Algorithm

The RSA Encryption algorithm uses a public key and a private key to encrypt and decrypt information without having to agree on a key before hand.

The strength of this algorithm is built around the fact that factoring large numbers is mathematically difficult. i.e. it is easy to tell that 13 * 31 = 403, but it is more difficult to figure what the prime factors of 493 are

For more, and probably better, information, I recommend

By the way, the prime factors of 493 are 17 & 29