Authentication Protocols & Types

Authentication protocols are sets of rules and processes that allow systems, devices, or applications to verify the identity of a user or another system before granting access to resources. They’re like the “secret handshake” of the digital world—if you don’t do it right, you don’t get in.

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Why We Need Authentication Protocols

Without authentication, there’s no guarantee that the person/system accessing a resource is who they claim to be. Protocols provide:

• Security – Prevent unauthorized access.
• Confidentiality – Protect sensitive data.
• Integrity – Ensure data hasn’t been tampered with.
• Accountability – Keep track of who did what.

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Common Authentication Protocols

1. Password-Based Authentication

• How it works: The user enters a username and password, which is compared to stored credentials (often hashed).
• Pros: Simple and widely used.
• Cons: Vulnerable to brute-force, phishing, and password reuse attacks.
• Example: Basic login forms.

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2. Multi-Factor Authentication (MFA)

• How it works: Combines two or more factors:
  • Something you know (password)
  • Something you have (OTP, smart card)
  • Something you are (fingerprint, face ID)
• Pros: Significantly increases security.
• Cons: Slightly less convenient for users.
• Example: Google 2-Step Verification.

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3. Kerberos

• Type: Ticket-based authentication.
• How it works:
  1. User logs in and gets a ticket-granting ticket (TGT) from the Key Distribution Center (KDC).
  2. TGT is used to request service tickets for specific resources.
• Pros: Passwords aren’t sent over the network; efficient for internal networks.
• Cons: Complex setup.
• Example: Used in Windows Active Directory.

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4. NTLM (NT LAN Manager)

• How it works: Challenge–response mechanism where the server sends a challenge, and the client responds with an encrypted value.
• Pros: Better than sending passwords in plain text.
• Cons: Outdated, vulnerable to pass-the-hash attacks.
• Example: Legacy Windows environments.

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5. OAuth 2.0

• Type: Authorization protocol with authentication capabilities.
• How it works:
  • Lets a user grant third-party applications limited access to their resources without sharing passwords.
  • Uses access tokens.
• Pros: Widely used for API and web app integrations.
• Cons: Complex to implement securely.
• Example: “Sign in with Google” or “Login with Facebook”.

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6. OpenID Connect (OIDC)

• How it works: An identity layer built on OAuth 2.0 that provides user authentication.
• Pros: Combines authentication and authorization; widely supported.
• Cons: Relies on OAuth 2.0 security.
• Example: Single sign-on for web apps.

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7. SAML (Security Assertion Markup Language)

• Type: XML-based SSO protocol.
• How it works: Uses assertions to share authentication info between an Identity Provider (IdP) and Service Provider (SP).
• Pros: Good for enterprise single sign-on.
• Cons: Verbose XML structure; setup complexity.
• Example: Logging into multiple corporate apps after one login.

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8. RADIUS (Remote Authentication Dial-In User Service)

• How it works: Centralized server authenticates remote users connecting to a network.
• Pros: Centralized, supports MFA.
• Cons: Not encrypted end-to-end (only password is encrypted).
• Example: Enterprise Wi-Fi authentication.

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9. TACACS+

• How it works: Similar to RADIUS but encrypts the entire payload and separates authentication, authorization, and accounting (AAA).
• Pros: More secure than RADIUS.
• Cons: Cisco-proprietary.
• Example: Network device authentication in enterprises.

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10. FIDO2 / WebAuthn

• How it works: Passwordless authentication using cryptographic keys stored on devices.
• Pros: Very secure, phishing-resistant.
• Cons: Requires hardware or platform support.
• Example: Using a security key (YubiKey) to log in.

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Choosing the Right Protocol

It depends on:

• Use case (web app, internal network, API)
• Security level required
• Ease of integration
• Compliance requirements

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