Password Authentication Protocol (PAP)

The Password Authentication Protocol (PAP) is a basic but important method used to check who is accessing network services, especially in systems that use the Point-to-Point Protocol (PPP). PAP is easy to use because it simply verifies user credentials to allow network access. This simplicity comes with security risks since it sends passwords in a form that can be easily seen and stolen.

This article explains how PAP works, its features, and why it’s still used today. We will also look at its security risks and discuss safer alternatives to protect sensitive information. 

Understanding Password Authentication Protocol (PAP)

The Password Authentication Protocol (PAP) operates primarily in network environments where a simple authentication mechanism is sufficient. Typically used in conjunction with the Point-to-Point Protocol (PPP), PAP starts the authentication process when a client attempts to establish a connection with a server. During this initiation phase, the client sends a request to the server indicating its desire to authenticate its identity. This straightforward handshake sets the stage for the transmission of authentication details.

Once the initial request is made, PAP proceeds to the authentication phase where the client transmits its username and password directly to the server. These credentials are sent as plaintext, meaning they are not encrypted or hidden in any manner. This exposes them to potential interception by unauthorized parties who may be monitoring the network traffic. The server then receives these credentials and begins the process of verifying them against its stored records to determine if the access should be granted.

If the credentials provided by the client match those on the server then the access is granted, and the client is notified of the successful authentication. Conversely, the server rejects the authentication request if there is a mismatch. In some implementations the server might allow the client multiple attempts to enter the correct credentials, which could potentially open up vulnerabilities such as brute force attacks. This lack of robust security measures underscores the simplicity but also highlights the significant risks associated with using PAP in environments where security is a concern.

Configuration Steps for PAP

There is a small topology in which there are 2 routers namely R1 and R2. R1 has IP address 10.1.1.1/30 on s0/0 and R2 has IP address 10.1.1.2/30 on s0/0. 

First, we will create a local database on R1 by providing a username and password: 

R1(config)#username Router1 password GeeksforGeeks

Configuring local database on R2: 

R2(config)#username Router2 password GeeksforGeeks

Remember, by default HDLC is configured on Cisco routers therefore first we have to change the encapsulation to PPP and enable PAP. 

R1(config)# int s0/0
R1(config-if)#encapsulation ppp
R1(config-if)#ppp authentication pap
R1(config-if)#ppp pap sent-username Router2 password GeeksforGeeks

Enabling PAP on R2: 

R2(config)# int s0/0
R2(config-if)#encapsulation ppp
R2(config-if)#ppp authentication pap
R2(config-if)#ppp pap sent-username Router1 password GeeksforGeeks

Here, notice that username and password are case-sensitive. Also, on router R1 we have to give a username and password. 

Note: This command can also be used on the router which wants to authenticate (calling router) in case of one-way authentication i.e only the calling router will authenticate. If two-way authentication, i.e both client and remote device are going to authenticate to each other, is operating then we have to make a local database and use this command on both devices. 

In addition, if we want to use CHAP first and PAP as a backup when CHAP fails, we can configure it by the command. 

R1(config)#int s0/0
R2(config-if)#ppp authentication chap pap

Also if we want CHAP as a backup then use the command. 

R1(config)#int s0/0
R2(config-if)#ppp authentication pap chap

Where PAP is Used?

Password Authentication Protocol (PAP) is used in several contexts where simple, password-based authentication is sufficient, particularly in environments where high security is not the primary concern. Here’s where PAP is commonly used: 

• Dial-Up Networks: PAP is often used in dial-up networking where a user connects to the internet through a modem. In these scenarios, PAP facilitates the authentication of the user’s credentials (username and password) against the Internet Service Provider’s (ISP) systems. This usage has declined with the decrease in dial-up connections in favor of broadband and fiber connections.

• VPN Connections: Virtual Private Networks (VPNs) sometimes use PAP, especially in legacy systems where other more secure options are not available or compatible. PAP allows remote users to authenticate their credentials when accessing a network through a VPN tunnel.

• Point-to-Point Protocol (PPP) Links: In network configurations that use PPP, such as connections between two routers over serial links, PAP can be employed for authentication. PPP supports multiple authentication methods, and PAP is the simplest, used particularly where both endpoints are controlled, reducing the risk of credential interception.

• Network Access Servers (NAS): Network Access Servers, which provide access services to a larger network or the internet, might use PAP for authenticating connecting clients. This is common in smaller or less security-sensitive environments.

• Legacy Systems and Backward Compatibility: In older systems or networks where newer protocols are not supported due to hardware or software limitations, PAP remains a viable authentication option. It provides a basic level of security without the need for updates or changes to existing infrastructure.

Difference Between PAP and CHAP

Advantages of PAP over CHAP

• Ease of Implementation: PAP is simpler to implement and configure compared to CHAP, making it beneficial for environments where advanced security is not a priority.

• Compatibility: Due to its basic nature, PAP offers broad compatibility with older systems and devices that may not support the cryptographic functions required by CHAP.

• Lower Resource Usage: PAP does not involve cryptographic calculations, which reduces its processing requirements, making it suitable for older hardware or embedded systems with limited resources.

• Administrative Simplicity: PAP allows for easier troubleshooting and monitoring due to its straightforward mechanism, providing direct and immediate feedback on authentication failures.

Conclusion

Password Authentication Protocol (PAP) remains a simple yet effective authentication mechanism for certain scenarios, particularly where advanced security is not the primary concern. Its ease of implementation and compatibility with legacy systems make it a practical choice in environments that prioritize simplicity and resource efficiency over rigorous security measures. PAP’s straightforward approach allows for quick troubleshooting and minimal processing requirements, which can be advantageous in older or resource-constrained networks. For most applications, especially those requiring robust security, alternative protocols like CHAP are recommended due to their enhanced security features and ability to protect user credentials more effectively.

saurabhsharma56

Follow

Improve

Article Tags :

• Computer Networks