Password Authentication Protocol (PAP) Security Explained

The Password Authentication Protocol (PAP) is one of the oldest methods for verifying users in computer networks. While it was widely used in the past, it is now considered outdated and insecure. Businesses that rely on secure authentication should understand the risks of PAP and consider safer alternatives.

This guide will break down what Password Authentication Protocol (PAP) is, how it works, why it is vulnerable, and what businesses can do to secure their systems.

What is Password Authentication Protocol (PAP)?

Password Authentication Protocol (PAP) is a simple method used to authenticate users by sending a username and password in plaintext. It was originally designed for use in Point-to-Point Protocol (PPP) connections, which allowed computers to communicate over dial-up networks.

Because PAP sends credentials without encryption, it is vulnerable to attacks like eavesdropping and replay attacks. More secure alternatives like CHAP authentication and EAP are now preferred.

Key Features of PAP:

• Uses plaintext authentication (no encryption).
• Sends the username and password at the start of the session.
• The server either accepts or rejects the credentials.
• It does not provide mutual authentication (the client does not verify the server).

Despite its simplicity, PAP is no longer recommended due to security risks.

PAP Authentication Example (Step-by-Step)

Here’s how the Password Authentication Protocol (PAP) works in a basic authentication process:

1. User Requests Access: The user enters their username and password on a client device.
2. Credentials are Sent: The client sends the username and password in plaintext to the server.
3. Server Checks Credentials: The server verifies the information against its stored records.
4. Authentication Result: The server either grants access (if credentials match) or denies access (if they don’t match).

Since the password is sent without encryption, attackers can intercept and steal login credentials.

Why is PAP Authentication Considered Insecure?

PAP was developed in an era when encryption was not a priority. Today, cybersecurity threats are much more advanced, making PAP a high-risk authentication method.

Security Risks of PAP:

• Passwords are sent in plaintext, making them easy to intercept.
• No encryption or hashing, exposing user credentials to hackers.
• Vulnerable to replay attacks, where an attacker captures login data and reuses it to gain access.
• No protection against man-in-the-middle attacks, where a hacker intercepts data between the client and server.

Because of these weaknesses, PAP is rarely used in modern networks. Instead, businesses rely on more secure alternatives like CHAP authentication or multi-factor authentication (MFA).

What is the Difference Between PAP and CHAP Authentication?

Many businesses have replaced PAP with Challenge Handshake Authentication Protocol (CHAP), which offers better security. Here’s how they compare:

Feature	PAP (Password Authentication Protocol)	CHAP (Challenge Handshake Authentication Protocol)
Encryption	No encryption (sends plaintext passwords)	Uses challenge-response mechanism with hashing
Authentication Type	One-time authentication	Continuous authentication throughout session
Protection Against Replay Attacks	No protection	Prevents replay attacks with unique challenge each time
Mutual Authentication	No	Yes
Vulnerability to Attacks	High	Lower

CHAP authentication is a far better option for businesses that need secure authentication.

PAP Authentication in Python (Code Example)

Here’s a simple PAP authentication example using Python:

# Basic PAP Authentication Example
def authenticate(username, password):
    stored_username = "admin"
    stored_password = "securepass"

    if username == stored_username and password == stored_password:
        return "Authentication successful"
    else:
        return "Authentication failed"

# Example Usage
user_input = input("Enter username: ")
pass_input = input("Enter password: ")
print(authenticate(user_input, pass_input))

This script checks if a username and password match a stored value. Since PAP sends passwords in plaintext, this is not secure for real applications. Instead, use hashed authentication methods.

PAP Protocol Port Number & Technical Specifications

• Protocol Type: Password-based authentication
• Port Number: Uses TCP port 1723 (for PPTP VPNs using PAP authentication)
• Encryption: None (plaintext transmission)
• Mutual Authentication: No
• Industry Recommendation: Avoid using PAP in modern networks

Why is PureVPN’s White-Label VPN the Secure Choice for Businesses?

If you run a business, using an outdated authentication method like PAP puts your data at risk. Instead, PureVPN’s White-Label VPN offers a secure, modern authentication system to keep your users safe. 

Here’s how PureVPN protects businesses:

• Uses secure authentication methods like CHAP and EAP instead of PAP.
• Encrypts login credentials to prevent interception.
• Supports multi-factor authentication (MFA) for stronger security.
• Provides a customizable VPN solution for businesses looking to offer secure browsing to clients.

With PureVPN’s White-Label VPN, businesses can provide a branded, secure VPN service without dealing with authentication vulnerabilities.

Is PAP Authentication Still Relevant?

The Password Authentication Protocol (PAP) is outdated and insecure. It lacks encryption, making it easy for hackers to steal credentials. Businesses should avoid using PAP and switch to CHAP, EAP, or MFA for better protection.

If you’re looking for a secure authentication system, consider using PureVPN’s White-Label VPN to protect your users and offer advanced security features.