The Modelling and Analysis of Security Protocols: the CSP Approach

0.4. Public-key certificates and infrastructures

In our discussion above we have glossed over a difficulty of how the agents acquire the public keys of other users and be sure that they are valid, i.e. associated with the correct user. This is quite tricky, but a standard solution is to set up a trusted authority, known as the Certification Authority (CA), that issues certificates that authenticate public keys and binds them to the names of the users. A public-key certificate is basically a digital document that contains the name of the user along with their authorized public key and perhaps information about the lifetime of the key etc., all signed by the CA using its public key. We discuss digital signatures later. As long as the CA does not ...