12-july-2006ietf 66, montreal1 implementation experience with a new wireless eap method david mitton...
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12-July-2006 IETF 66, Montreal 1
Implementation Experience with a New Wireless EAP Method
David Mitton
RSA Security, Inc.
12-July-2006 IETF 66, Montreal 2
New EAP Method 32, SecurID Token Authentication
• Uses Protected-OTP EAP Frameworkdraft-nystrom-eap-potp-04.txt
• EAP Method 32 - profile of POTP for RSA SecurID
• Applications:– Dial PPP– VPN (PPTP)– Wired 802.1x– 802.11i Wireless 802.1x
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Problems with Wireless Deployment
• Development and testing on single vendor access point worked flawlessly
• When deployed to the field, began getting problem reports
• Three different vendors; three different types of problems
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Typical Components Diagram
802.1xAuthentication
802.11
SDEAP.DLL
Token AuthToken Auth
SDEAP.DLL
802.1x Authentication
RADIUS Server
AS Client
Secured Access Protocol
AAA ServerRemote Access
Client
RADIUS Client
EAP Authenticator
802.11
802.1x Authentication
Wireless Access Point
Username, Passcode
AS API
POTP Resolver
OTP Auth Server
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Typical Message Flow
802.11 STA Access Point AAA Server EAP Server
EAPOL Identity Request
EAPOL Start
EAPOL Identity Response RADIUS Access-Request EAP Identity Response
EAP Method RequestRADIUS Access-ChallengeEAP Method Request
EAP Method Response RADIUS Access-Request EAP Method Response
EAP Success w/KeysRADIUS Access-SuccessEAPOL Success
EAPOL Handshake
EAPOL Handshake
EAP Client
EAP Identity Request
EAP Identity Response
EAP Method Request
EAP Method Response
EAP Success
Key Return
EAP Interface EAPOL Protocol RADIUS Protocol EAP Interface
Repeat as needed...
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Case 1: Response Not Accepted
• EAP 32 Request message is forwarded from AP to STA, but AP returns EAP Failure upon receiving response.
• AP decides to block EAP based on method value.
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Case 2: Fumbled Forwarding
• EAP32 Request passes from RADIUS to EAPOL but not the Response
• Method dependencies in the code that packs and unpacks EAP messages from RADIUS messages
• Causes the AP to retransmit Request every 30 seconds. STA responds each time, but Response is lost
• Session-Timeout value (120) ignored by AP
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Case 3: Session Interference
• Re-sync condition causes a long authentication, AP decides to send new Identity Request to STA in midst of exchange. (2.5 seconds after previous exchange)
• AP has bad policy on length of authentication process. Not tied to message exchange.
• Did not honor Session-Timeout attribute in Access-Challenge.
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Bad Assumptions
• Method type #s should all be passed, or be management configurable
• Avoid method dependent processing for EAP forwarding – why?
• Session timeout should: – use Session-Timeout attribute, – sensitive to message ID change, and
message to message timing, not overall elapsed time
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Suggested Testing Requirements
• Allow all method values
• Retransmission of individual messages should be manageable (Session-Timeout)
• Timeout of authentication session should be tied to session inactivity not arbitrary or inaccessible numbers
• Anything that returns keys should work (e.g. meets RFC 3748)
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How do we get Open and Interoperable EAP products?
• Products that only support a short list of protocols are preventing new security!
• Who is responsible?– Vendors?– Wi-Fi Alliance?– IEEE 802.11?
• What can we do here?