Kerberos

A widely used authentication protocol developed at the Massachusetts Institute of Technology (MIT). In “classic” Kerberos, users share a secret password with a Key Distribution Center (KDC). The user, Alice, who wishes to communicate with another user, Bob, authenticates to the KDC and is furnished a “ticket” by the KDC to use to authenticate with Bob. When Kerberos authentication is based on passwords, the protocol is known to be vulnerable to off-line dictionary attacks by eavesdroppers who capture the initial user-toKDC exchange. Longer password length and complexity provide some mitigation to this vulnerability, although sufficiently long passwords tend to be cumbersome for users.
SOURCE: SP 800-63

A means of verifying the identities of principals on an open network. It accomplishes this without relying on the authentication, trustworthiness, or physical security of hosts while assuming all packets can be read, modified and inserted at will. It uses a trust broker model and symmetric cryptography to provide authentication and authorization of users and systems on the network.
SOURCE: SP 800-95