Final answer:
IPsec uses digital certificates and Kerberos to authenticate the identities of communicating devices. Pre-shared keys are also used, although not specifically termed 'Multi-shared key'. PAM is not an authentication method used by IPsec.
Step-by-step explanation:
IPsec, which stands for Internet Protocol Security, uses various methods to authenticate the identity of communicating devices. Among these methods, digital certificates and Kerberos are used for authentication. While there is no method specifically labeled "Multi-shared key," IPsec does support the use of a pre-shared key for authentication purposes. This concept is similar to 'Multi-shared key,' as it involves a key value that both parties share in advance and keep secret from others. Pre-shared keys work on the basis of something both parties know.
The option labeled 'PAM' or Pluggable Authentication Modules is not directly associated with IPsec, but is instead a suite of libraries for dynamic authentication support for different applications and services in a system. However, PAM itself isn't a method used by IPsec for authentication.
- Digital certificates: These rely on a trusted Certificate Authority (CA) to issue a certificate that verifies the identity of the holder. Digital certificates are part of the Public Key Infrastructure (PKI) and are used extensively for secure communications on the internet.
- Kerberos: This is a network authentication protocol that works on the basis of tickets to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. Kerberos is often used in conjunction with IPsec for authentication.