Authentication Basics

What is Authentication?

Authentication is the process of verifying the identity of a user, system, or application. It ensures that the entity attempting to access a resource is who or what it claims to be. Authentication is a critical component of security and serves as the first line of defense against unauthorized access.

Authentication should not be confused with authorization, which determines what an authenticated entity is allowed to do. Authentication verifies identity, while authorization grants access rights.

One-way Authentication

One-way authentication is a process where only one party in a communication verifies the identity of the other. The most common example is a client authenticating to a server, but the server does not authenticate back to the client.

Example: When you log into a website with a username and password, you are authenticating yourself to the server, but you typically don't verify the server's identity (although HTTPS provides some implicit verification).

Security Considerations: One-way authentication is vulnerable to man-in-the-middle attacks where an attacker can impersonate the non-authenticating party.

Password-based Authentication

Password-based authentication is the most common form of authentication, where users provide a secret password to verify their identity. The system compares the provided password with a stored reference (usually a hash) to authenticate the user.

Key Components:

• Password storage: Passwords should never be stored in plaintext but should be hashed using strong algorithms like bcrypt, Argon2, or PBKDF2.
• Password policies: Requirements for length, complexity, and rotation.
• Account lockout: Temporarily disabling accounts after multiple failed attempts.

Weaknesses: Password-based authentication is vulnerable to various attacks, including brute force, dictionary attacks, phishing, and password reuse across multiple services.

Certificate-based Authentication

Certificate-based authentication uses digital certificates to verify the identity of users or systems. These certificates are issued by trusted Certificate Authorities (CAs) and contain the public key of the entity along with identity information.

How it works:

1. The client presents its digital certificate to the server.
2. The server verifies the certificate's digital signature using the CA's public key.
3. The server checks if the certificate is valid, not expired, and not revoked.
4. If verification succeeds, the client is authenticated.

Applications: SSL/TLS client certificates, smart cards, and Public Key Infrastructure (PKI) systems.

Advantages: Stronger than passwords, resistant to phishing, and can be combined with hardware tokens for enhanced security.

Mutual Authentication

Mutual authentication (two-way authentication) is a process where both parties in a communication verify each other's identity. This provides stronger security than one-way authentication by ensuring that both the client and server are legitimate.

Implementation Methods:

• TLS with client certificates: Both server and client present certificates.
• Challenge-response protocols: Each party issues a challenge that the other must respond to correctly.
• Kerberos: Uses trusted third-party authentication servers to verify both parties.

Benefits: Protects against man-in-the-middle attacks and server impersonation, providing a higher level of trust in the communication channel.