10.1 What is a digital certificate?
Remember from Chapter 7, Public-Key Cryptography, that public keys, more precisely their numerical representation and their relation to a certain entity, must be authentic. Otherwise, an attacker, Eve, might exchange her own public key with Alice’s and could read Alice’s messages. Digital signatures, on the other hand, create the same need for authentic public keys: If Eve manages to exchange PKAlice with her own public key, she can sign with her own private key but claim that the signature was created by Alice, with potentially catastrophic consequences for Alice.
Yet, so far, we have not discussed how we can achieve authenticity for public keys in the best possible way. Luckily, digital signatures, as discussed in the last chapter, provide us with a way to ensure authenticity. What we need is a digitally signed statement that binds together a public key with a corresponding entity. These statements are so important that they have...