Password Authentication Protocol

Password Authentication Protocol (PAP) is a password-based authentication protocol used by Point to Point Protocol (PPP) to validate users. Almost all network operating system remote servers support PAP. PAP is specified in RFC 1334.

PAP is considered a weak authentication scheme (weak schemes are simple and have lighter computational overhead but are much more vulnerable to attack; while weak schemes may have limited application in some constrained environments, they are avoided in general). Among PAP's deficiencies is the fact that it transmits unencrypted passwords (i.e. in plain-text) over the network. PAP is therefore used only as a last resort when the remote server does not support a stronger scheme such as CHAP or EAP.

Working cycle

PAP authentication is only done at the time of the initial link establishment, and verifies the identity of the client using a two-way handshake.

  1. Client sends username and password. This is sent repeatedly until a response is received from the server.
  2. Server sends authentication-ack (if credentials are OK) or authentication-nak (otherwise)[1]

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 Message
Authentication-nak Code = 3 ID Length Message length Message

PAP packet embedded in a PPP frame. The protocol field has a value of C023 (hex).

Flag Address Control Protocol (C023 (hex)) Payload (table above) FCS Flag
gollark: Apparently the plan is to try and keep the number of cases manageable but not keep people too isolated by changing the "restrictions" (recommendations right now) for a year or so.
gollark: The UK appears to mostly be going for just *asking* people not to go out much right now, and obviously shutting schools.
gollark: That doesn't make it a good idea.
gollark: And after the panic-buying began there was, well, not much food available, so it made (makes?) *some* sense to buy some when it is.
gollark: There was a possibility (probably still is, and I imagine it's happened some places) of supply chains failing to get food to sale fast enough.

See also

Notes
  1. Forouzan (2007). Data Commn & Networking 4E Sie. McGraw-Hill Education (India) Pvt Limited. pp. 352–. ISBN 978-0-07-063414-5. Retrieved 24 November 2012.

References
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