What are the most common VPN authentication methods?

1 Password Authentication Protocol (PAP)

PAP is one of the simplest and oldest VPN authentication methods. It uses a username and password combination to identify the VPN client to the VPN server. The client sends the username and password in plain text over the VPN tunnel, and the server checks them against a database or a directory service. PAP is easy to implement and compatible with many VPN protocols and devices. However, it is also very insecure, as anyone who intercepts the VPN traffic can see the credentials and use them to access the network. PAP is not recommended for modern VPNs, unless it is combined with other security measures.

2 Challenge Handshake Authentication Protocol (CHAP)

CHAP is an improvement over PAP that adds a challenge-response mechanism to the password authentication process. Instead of sending the password in plain text, the client sends a hashed value of the password and a random challenge string generated by the server. The server then compares the hashed value with its own calculation based on the password and the challenge string. If they match, the authentication is successful. CHAP prevents replay attacks and password sniffing, as the challenge string changes every time and the password is never transmitted in clear text. However, CHAP still relies on a shared secret (the password) that can be compromised or guessed by brute force.

3 Extensible Authentication Protocol (EAP)

EAP is a flexible and extensible VPN authentication method that supports multiple types of credentials and mechanisms. EAP can use passwords, certificates, tokens, smart cards, biometrics, or other factors to authenticate the VPN client to the server. EAP also allows for dynamic negotiation of the authentication method and parameters between the client and the server, depending on their capabilities and preferences. EAP can work with different VPN protocols and transport layers, such as IPsec, SSL/TLS, or PPP. EAP can provide strong security and convenience for VPN users, but it also requires more configuration and management than simpler methods.

4 Certificate-Based Authentication

Certificate-based authentication is a VPN authentication method that uses digital certificates to verify the identity and trustworthiness of the VPN endpoints. Digital certificates are electronic documents that contain information about the entity (user or device) and a public key that corresponds to a private key. The certificates are issued and signed by a trusted authority (CA) that vouches for their validity. The VPN client and server exchange their certificates and verify their signatures and expiration dates. They also use their public and private keys to encrypt and decrypt the data and establish a secure session key. Certificate-based authentication is one of the most secure and reliable VPN authentication methods, as it eliminates the need for passwords or other shared secrets that can be stolen or compromised. However, it also requires more infrastructure and maintenance than other methods.

5 Multi-Factor Authentication (MFA)

MFA is a VPN authentication method that combines two or more factors to increase the security and assurance of the VPN endpoints. The factors can be something the user knows (such as a password or a PIN), something the user has (such as a token or a smart card), or something the user is (such as a fingerprint or a face scan). The VPN client and server require the user to provide all the factors before granting access to the network. MFA can prevent unauthorized access even if one factor is compromised or lost, as the attacker would need to obtain all the factors to impersonate the user. MFA can also improve the user experience and convenience, as some factors can be automated or integrated with other devices. However, MFA can also introduce more complexity and cost to the VPN setup and management, as it requires more hardware, software, and policies than other methods.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?