Explanation
IPsec is a collection of protocols and algorithms used to protect IP packets at Layer 3 (hence the name of IP
Security [IPsec]). IPsec provides the core benefits of confidentiality through encryption, data integrity through
hashing and HMAC, and authentication using digital signatures or using a pre-shared key (PSK) that is just for
the authentication, similar to a password.
Source: Cisco Official Certification Guide, IPsec and SSL, p.97