PPP, PAP and CHAP

PPP
PPP is common encapsulation type, which supports TCP/IP, AppleTalk and IPX.
It works at the data link layer of the OSI model to encapsulate data over a point-to-point connection.
PPP breaks down into three primary pieces:
NCP (Network Control Protocol)
THE NCP identifies which network layer protocol the data pertains to.
LCP (Link Control Protocol)
Used for establishing, authenticating and maintaining a connection
HDLC Used to encapsulate information


At the Physical layer, the PPP configure a range of interfaces, including:

• Asynchronous serial
• Synchronous serial
• HSSI
• ISDN

PPP operates across any DTE/DCE interface (RS-232-C, RS-422, RS-423, or V.35)

PAP and CHAP are authentication methods of PPP.

PAP
Provides a simple method for a remote node to establish its by using a two way handshake.
When the authentication is used to login the information is send as one LCP package. After the authentication is received the server either allows or denies it entry. PAP’s authentication method is vulnerable to eavesdroppers, since they can obtain the password by listening in on the serial line, and by using repeated trial and error attacks.

CHAP
In CHAP authentication , the server sends a randomly generated “challenge” string to the client, along with its hostname. The client uses the hostname to look up the appropriate secret, combines it with the challenge, and encrypts the string using a one-way hashing function. The result is returned to the server along with the client's hostname. The server now performs the same computation, and acknowledges the client if it arrives at the same result.