Kerberos
A ticket-based authentication protocol from the 1980s that still runs under every Active Directory login — you prove yourself once and use encrypted tickets to reach services after.
Kerberos avoids sending passwords over the network at all: a client authenticates once to a trusted third party and receives a ticket, which it presents to services instead of credentials. It’s the authentication engine underneath Active Directory — which is why “Kerberos ticket” attacks like Golden and Silver Ticket are among the most serious domain-compromise techniques in enterprise environments.