Redemption Steps

We strongly recommend off-the-shelf protocols such as SSL/TLS or Kerberos when theyre done right! Make sure that you are doing all the required actions to perform proper authentication (for example, see Sin 10). Also, make sure that the resulting key exchange is used to provide ongoing authentication services. This will generally happen automatically when youre using SSL/TLS. (The quality of the authentication tends to be more likely to be suspect.) However, with other systems, the end result may be a key, where youre the one responsible for using the key properly.

Dont design your own protocol. Too many subtle things can go wrong. If you think you need a custom protocol, have a cryptographer do it. While we could give you a checklist of properties to ensure, it would only lead you to a false sense of security. In the world of cipher design, its a common adage that everyone can build a cipher he or she cannot break, but its a rare bird who can build something that wont be broken by the cryptographic community. The same goes true for authentication and key exchange protocols.

If you have a preexisting protocol that is custom-built, consider migrating to an off-the-shelf solution, where the set of things that could go wrong are small and well understood , such as SSL/TLS. Otherwise, we suggest you have a cryptographer analyze the protocol, preferably by providing a proof of security, or at least demonstrating resistance to known attacks in the cryptographic literature, and having that peer reviewed.