15.5 X.509 Certificates
Suppose you want to buy something on the Internet. You go to the website Gigafirm.com, select your items, and then proceed to the checkout page. You are asked to enter your credit card number and other information. The website assures you that it is using secure public key encryption, using Gigafirm’s public key, to set up the communications. But how do you know that Eve hasn’t substituted her public key? In other words, when you are using public keys, how can you be sure that they are correct? This is the purpose of Digital Certificates.
One of the most popular types of certificate is the X.509. In this system, every user has a certificate. The validity of the certificates depends on a chain of trust. At the top is a ...
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