In 1975, Whitfield Diffie and Martin Hellman proposed a different sort of relationship between encryption and decryption keys. What if encryption and decryption were performed using two different, but related, keys? The consequences turned out to be quite radical. What we get is what is known as "public-key" or "asymmetric" algorithms.

The previous section of this tutorial discussed the general concept of public-key encryption. Here, we will hop right into a look at some actual public-key algorithms.

The most popular public-key algorithm by far is called RSA (after its creators, Ronald L. Rivest, Adi Shamir, and Leonard M. Adleman). For years, the only real hindrance to RSA's even more widespread use was its patent status; however, that patent recently expired, and the algorithm is now in the public-domain. The El Gamal scheme runs a somewhat distant second and is based on the difficulty of calculating discrete logarithms in a finite field. RSA is based on the difficulty of factoring, and will be the only public-key algorithm discussed in greater detail in this tutorial.