Chapter 17
Key Servers

At last we turn to key management. This is, without a doubt, the most difficult issue in cryptographic systems, which is why we left it to near the end. We've discussed how to encrypt and authenticate data, and how to negotiate a shared secret key between two participants. Now we need to find a way for Alice and Bob to recognize each other over the Internet. As you will see, this gets very complex very quickly. Key management is especially difficult because it involves people instead of mathematics, and people are much harder to understand and predict. Key management is in many ways a capstone to all we have discussed so far. Much of the benefit of cryptography is defeated if key management is done poorly.

Before we start, let us make one thing clear. We talk only about the cryptographic aspects of key management, not the organizational aspects. The organizational aspects include things like a policy covering whom to issue keys to, which keys get access to...