1. EAP Method Requirements for Emergency Services
May 2007
doc.: IEEE /0508r0
May 2007
EAP Method Requirements for Emergency Services
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Matthew Gast, Trapeze Networks
Matthew Gast, Trapeze Networks

2. May 2007
doc.: IEEE /0508r0
May 2007
Abstract
This presentation discusses requirements for the EAP method for use with emergency calls over networks, and is intended to serve as a basis for asking the IETF to recommend an EAP method for such a deployment scenario.
Matthew Gast, Trapeze Networks
Matthew Gast, Trapeze Networks

3. Types of Emergency Calls in 802.11u
May 2007
doc.: IEEE /0508r0
May 2007
Types of Emergency Calls in u
Unencrypted calls on networks using the Emergency Services Only (ESO) bit for signaling
APs advertising the ESO bit will accept any non-AP STA without L2 security
Network responsible for enforcing access control to only VoIP services with VLANs, ACLs, etc.
Encrypted calls using public credentials
Network is shared with other uses
Default Emergency Services NAI gives non-AP STAs a user name to send in 802.1X/EAPOL to get access to emergency services
Key exchange for L2 data security requires a PMK, which must be exchanged by either PSK or EAP method
Regulatory requirements may require use of link encryption, which forces use of the public credential case
Matthew Gast, Trapeze Networks
Matthew Gast, Trapeze Networks

4. Why not just use a PSK? The PSK must be widely known
May 2007
doc.: IEEE /0508r0
May 2007
Why not just use a PSK?
The PSK must be widely known
It should be the same for every network in the world, so that a phone can be used in any network for emergency services
The only practical way to get this to happen is to put the PSK into the standard, where everybody can read it
PSKs can have poor DoS resistance
Matthew Gast, Trapeze Networks
Matthew Gast, Trapeze Networks

5. EAP Issues with Emergency Calls
May 2007
doc.: IEEE /0508r0
May 2007
EAP Issues with Emergency Calls
Negotiating compatible method may take time
This is a problem for TGu to solve
Existing EAP methods were designed for closed networks
OK to have pre-configured trust relationships, and important to get cryptography right
May depend on reachability of AS
Should be an optional implementation choice for AP vendor to do something simple
Matthew Gast, Trapeze Networks
Matthew Gast, Trapeze Networks

6. Requirement #1: No Pre-configured Trust Relationship
May 2007
doc.: IEEE /0508r0
May 2007
Requirement #1: No Pre-configured Trust Relationship
Every network that uses public credentials for emergency services needs to identify itself
Credentials (PSK or certificate) should not be published
PSK has scaling problems and potential security issues
Implementations should not require multiple certificate chains to validate trust because many devices will have small storage (e.g. phones); single certificate may be challenging
Anonymous cryptography is acceptable, since the network will need to manage access rights as part of allowing session establishment
Matthew Gast, Trapeze Networks
Matthew Gast, Trapeze Networks

7. Requirement #2: “Small” Number of Messages
May 2007
doc.: IEEE /0508r0
May 2007
Requirement #2: “Small” Number of Messages
Emergency calls are a lower security bar
Users are anonymous at L2 in this scenario – user accounts not required
Acceptable to eliminate some crypto features (e.g. perfect forward secrecy) to reduce message count and handshake time
Implementation of L2 security within AP should be possible; some networks may look up access rights via AS
Each round-trip message adds latency
Wireless latency is small, AP-to-AS latency can be larger depending on deployment
Matthew Gast, Trapeze Networks
Matthew Gast, Trapeze Networks