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Security Fundamentals & Crypto · Foundational

Remote Authentication Dial-In User Service (RADIUS)

AAA protocol commonly used for network access, using UDP 1812 (authentication) and 1813 (accounting).

Definition

RADIUS combines authentication and authorization and encrypts only the password attribute in transit, using a shared secret with MD5. It is the standard back end for 802.1X, VPNs, and Wi-Fi enterprise authentication. After the 2024 Blast-RADIUS vulnerability, the Message-Authenticator attribute and RADIUS over TLS (RadSec) are recommended.

Example

A wireless controller forwards EAP messages to a Cisco ISE RADIUS server for user authentication.

Exam tip

RADIUS = UDP, encrypts password only, combines authN/authZ; TACACS+ = TCP 49, encrypts everything, separates AAA.

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