A nice and layman introduction to encryption as used for digital signing, based on private/public keys and Certification Authorities (CA), and how that relates to the upcoming Gatekeeper security feature of Mac OSX Mountain Lion (10.8).
In this series, you’ll learn how RSA and DSA authentication work, and see how to set up passwordless authentication the right way. In the first article of the series, Daniel Robbins focuses on introducing the RSA and DSA authentication protocols and showing you how to get them working over the network.
Part 2 here.
Part 3 here.