Skip to Main Content
RADIUS
book

RADIUS

by Jonathan Hassell
October 2002
Intermediate to advanced content levelIntermediate to advanced
206 pages
8h 30m
English
O'Reilly Media, Inc.
Content preview from RADIUS

Authenticator

The authenticator region, often 16 octets long, is the field in which the integrity of the message’s payload is inspected and verified. In this field, the most important octet is transmitted before any other—the value used to authenticate replies from the RADIUS server. This value is also used in the mechanism to conceal passwords.

There are two specific types of authenticator values: the request and response values. Request authenticators are used with Access-Request and Accounting-Request packets. In the request value, the field is 16 octets long and is generated on a completely random basis so as to thwart any attacks. While RADIUS doesn’t make a provision for protecting communication against wiretapping and packet capture, random values coupled with a strong password make attacking and snooping difficult.

The response authenticator is used in Access-Accept, Access-Reject, and Access-Challenge packets. The value is calculated using a one-way MD5 hash generated from the values of the code, identifier, length, and request-authenticator regions of the packet header, followed by the packet payload and the shared secret. (I’ll cover shared secrets in detail later in this chapter.) Example 2-1 shows an equation to represent how this hash is computed.

Example 2-1. From RFC 2865, the MD5 hash for the response authenticator header field
ResponseAuth = MD5(Code+ID+Length+RequestAuth+Attributes+Secret)
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

TCP/IP Illustrated, Volume 1: The Protocols, 2nd Edition

TCP/IP Illustrated, Volume 1: The Protocols, 2nd Edition

Kevin R. Fall, W. Richard Stevens
TCP/IP Guide

TCP/IP Guide

Charles M. Kozierok

Publisher Resources

ISBN: 0596003226Errata Page