Certificates to identify which peers to trust and also to earn the trust of those peers in kind.
Client and server exchange these certificates during the handshake phase of a TLS connection.
Server Authentication
This is the most common form of TLS authentication: clients verify that servers are trusted
and that they own the hostnames that they represent. Server authentication is required.
To perform server authentication:
- The server's handshake certificates must have a held
certificate (a certificate and its private key). The certificate's subject alternative
names must match the server's hostname. The server must also have is a (possibly-empty)
chain of intermediate certificates to establish trust from a root certificate to the
server's certificate. The root certificate is not included in this chain.
- The client's handshake certificates must include a set of trusted root certificates. They
will be used to authenticate the server's certificate chain. Typically this is a set of
well-known root certificates that is distributed with the HTTP client or its platform. It
may be augmented by certificates private to an organization or service.
Client Authentication
This is authentication of the client by the server during the TLS handshake. Client
authentication is optional.
To perform client authentication:
- The client's handshake certificates must have a held
certificate (a certificate and its private key). The client must also have a
(possibly-empty) chain of intermediate certificates to establish trust from a root
certificate to the client's certificate. The root certificate is not included in this
chain.
- The server's handshake certificates must include a set of trusted root certificates. They
will be used to authenticate the client's certificate chain. Typically this is not the same
set of root certificates used in server authentication. Instead it will be a small set of
roots private to an organization or service.