In Chapter 1, we described a scenario known as a man-in-the-middle attack, in which an attacker could intercept and even manipulate communications secured with public key cryptography. The attack is possible because public key cryptography provides no means of establishing trust when used on its own. Public Key Infrastructure (PKI) provides the means to establish trust by binding public keys and identities, thus giving reasonable assurance that we're communicating securely with who we think we are.
Using public key cryptography, we can be sure that only the encrypted data can be decrypted with the corresponding private key. If we combine this with the use of a message digest algorithm to compute a signature, we can be sure that the encrypted data has not been tampered with. What's missing is some means of ensuring that the party we're communicating with is actually who they say they are. In other words, trust has not been established. This is where PKI fits in.
In the real world, we often have no way of knowing firsthand who a public key belongs to, and that's a big problem. Unfortunately, there is no sure-fire way to know that we're communicating with who we think we are. The best we can do is extend our trust to a third party to certify that a public key belongs to the party that is claiming ownership of it.
Our intention in this chapter is to give you a basis for understanding how PKI fits into the big picture. PKI is important to ...