Password Authentication Protocol (PAP)

The Password Authentication Protocol (PAP) provides simple password authentication on initial link establishment. It is not a strong authentication method, since passwords are transmitted in clear over the link and there is no protection from repeated attacks during the life of the link.

When PAP authentication is requested by one end of the link during the link establishment phase, the other end must respond with a valid and recognized identifier and password pair. If it fails to respond, or if either the identifier or password are rejected, authentication fails and the link is closed.

PAP authentication may be requested by one end of the link only, or by both ends of the link simultaneously. If both ends request PAP authentication, they exchange identifiers and passwords. Authentication must be successful at both ends, or the link is closed.