Password authentication protocol

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Password Authentication Protocol, sometimes abbreviated PAP, is a simple authentication protocol used to authenticate a user to a network access server used for example by internet service providers. PAP is used by Point to Point Protocol. Authentication is a process of validating a user before accessing the resources. Almost all network operating system remote servers support PAP.

PAP transmits unencrypted ASCII passwords over the network and is therefore considered insecure. It is used as a last resort when the remote server does not support a stronger authentication protocol, like CHAP or EAP (while the last is actually a framework).

[edit] Working cycle

Client sends username and password
Server sends authentication-ack (if credentials are OK) or authentication-nak (otherwise)

[edit] PAP Packets

Description	1 byte	1 byte	2 bytes	1 byte	Variable	1 byte	Variable
Authentication-request	Code = 1	ID	Length	Username length	Username	Password length	Password
Authentication-ack	Code = 2	ID	Length	Message length	Username
Authentication-nak	Code = 3	ID	Length	Message length	Username