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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

CHAP

CHAP is based on the premise that the password should never be sent in any packet across a network. CHAP dynamically encrypts the requesting user’s ID and password. The user’s machine then goes through its logon procedure, having obtained a key from the RADIUS client equipment of at least 16 octets in length. The client then hashes that key and sends back a CHAP ID, a CHAP response, and the username to the RADIUS client. The RADIUS client, having received all of the above, places the CHAP ID field into the appropriate places in the CHAP-Password attribute and then sends a response. The challenge value originally obtained is placed in either the CHAP-Challenge attribute or in the authenticator field in the header—this is so the server can easily access the value in order to authenticate the user.

To authenticate the user, the RADIUS server uses the CHAP-Challenge value, the CHAP ID, and the password on record for that particular user and submits it to another MD5 hashing algorithm. The result of this algorithm should be identical to the value found in the CHAP-Password attribute. If it’s not, the server must deny the request; otherwise, the request is granted.

The fact that the password in a CHAP transaction is never passed across the network is just one reason why CHAP is an appealing authentication protocol. How does this work? The user data against which the hashing routine is run returns a one-way value that does not contain the password. So the server must have the current ...

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Publisher Resources

ISBN: 0596003226Errata Page