Secure and Efficient Network Access

1. Secure and EfficientNetwork Access DIMACS Workshop, November 3rd, 2004, Piscataway, NJ, USA Jari Arkko Ericsson Research NomadicLab Pasi Eronen Nokia Research Center Pekka Nikander Vesa Torvinen Ericsson Research NomadicLab This presentation has been produced partially in the context of the Ambient Networks Project. The Ambient Networks Project is part of the European Community's Sixth Framework Program for research and is as such funded by the European Commission. All information in this document is provided ``as is'' and no guarantee or warranty is given that the information is fit for any particular purpose. The user thereof uses the information at its sole risk and liability. For the avoidance of all doubts, the European Commission has no liability in respect of this document, which is merely representing the authors view

2. Presentation Outline • The Problem • Ongoing work • Some new ideas • An example protocol run • Conclusions

3. The Problem

4. Some Problems in Current Network Access Approaches (1/3) - Efficiency • Attachment involves a large number of messages • Scanning & 802.11 attachment • 802.1X and EAP messaging • 802.11i four-way handshake • DNA & IP router and neighbor discovery • Address autoconfiguration, DAD • Mobile IP home registration • Mobile IPv6 correspondent node registration • Over 50% of this is due to security • Request/Response style, even across the Internet • Amount of data is growing with certificates, configuration, and discovery • Multiple mandatory waiting periods • Even a second, such as for DAD • Iteration over available accesses

5. Some Problems in Current Network Access Approaches (2/3) - Security • “I’m one of the trusted network nodes” approach • Sufficient for large cell size, well protected base stations • Not very good for devices on the coffee shop wall • Focus on authentication, not authorization • Does everyone know/agree with the service parameters ? • Denial-of-Service problems • Use of cryptographic keys very late in the process • Attacks that create/leave state to network side elements • Insecure lower-layer “detach” messages • 802.11 countermeasures functionality • Privacy protection is non-existent or incomplete

6. Some Problems in Current Network Access Approaches (3/3) - Functionality • Security models do not fit all types of deployment • Credit card payments • Home deployments (e.g. leap of faith or physical connection instead of a certificate exercise) • Configuration, discovery, and movement support • What are the IP parameters that I can get from this access point? • Is my home operator available via this access point? • How much would accessing this network cost? • Could the network tell me when to move, and to what channel and parameters to use?

7. Ongoing Work

8. Ongoing Work to Address the Problems... • IP mobility • Better implementations that employ parallism allowed by the RFCs • Faster route optimization schemes, such as moving tasks out of the critical path • Address autoconfiguration • Turning DAD off • Optimistic DAD • DHCP and SEND security

9. Ongoing Work, Continued • DNA, Router and Neighbor Discovery • Faster algorithms for detecting whether or not movement has occurred • More frequent and precise router advertisements • Elimination “first message” delays from RFC 2461 • SEND security • EAP authentication • Methods work (new credentials, deployment, …) • Channel binding and parameter authentication

10. Ongoing Work, Continued • Link layer • Pre-authentication and proactive key distribution • Better protection of payload packets (AES etc) • Better information channels from the network to the clients (e.g., 802.21) • Discovery (WIEN SG) • Faster scanning techniques, parameter tuning • Bigger subnets (less IP layer work after attachment) • ...

11. Observations • People care about this! • A lot of results! • Most work focused on a particular “slice” of the problem • No good understanding of what the impact of individual improvement is for effiency • E.g., “I can’t afford 1 RTT in Mobile IP” • Not enough system-level understanding of the security issues

12. Some New Ideas

13. Approach • Focus on the problem as a whole! • There are multiple parties involved -- not just two • Who needs to communicate with who? • How are the parties identified? • What is the optimal order of messages? • What system security properties are needed? • Are there bulk information transfer needs? How can they best be addressed? • Can we learn something from solutions in other contexts?

14. Caveat • This may not be compatible with current protocols • Layer-purists might object to our views • We do not have all the details, just pointers to ideas

15. Potential Solution Ingredients (1/5) Addressing: • All nodes (not just the client) need an address • Addresses are hashes of public keys • Benefits: • All parties -- such as the “access network” can be addressed in communications • Avoid address stealing and functionality to bind addresses to credentials • Nodes can generate their addresses and keys on their own, without infrastructure • Privacy can be achieved via ephemeral keys • Identifier vs. routing semantics

16. Potential Solution Ingredients (2/5) Message order: • Find out what information the whole problem involves, and how many messages need to carry it • And re-think message order • Example: If the client’s IP address was known earlier, the authentication process with the home network could handle mobility-related registrations as well • Benefits: • Number of messages can be reduced • “Ping-pong” delays can be avoided

17. Potential Solution Ingredients (3/5) Information transfer: • Do not fetch everything from the original source • Cache information about, say, roaming consortium in the AP • Learn from TCP… no req-resp across the Internet • Either run TCP-like protocols directly between the client and the, say, home network • Or have the access point do this over the Internet, and use a request-response over the final radio hop • Information transfer capabilities should not be restricted to the initial authentication exchange • Benefits • More and faster information transfer, at any time

18. Potential Solution Ingredients (4/5) Miscallenous • Delegation • Does the client have to be involved in tasks? • Can some tasks be delegated to the access point/router? • For instance, router based address assignment and DAD • Even a mobility related registration could be delegated • Denial-of-Service protection • No separation to “attachment” and “secure attachment” • Stateless design on the network side

19. Potential Solution Ingredients (5/5) Miscallenous, continued • Privacy protection • Build the protocols for non-static identifiers and addresses • Protect communications from the start, not at the end

20. An Example Protocol Run

21. The Example Flows: • Current message flow • Suggested basic message flow • Variant with better mobility support • Handoff Assumptions: • Authentication needed; roaming case • IPv6 • Mobility with RO & one peer • Client - home authentication in 2 RTT (identifier / challenge / response / success)

22. Example: Current Flow

23. other node access network client home Beacon 802.11 Attachment 802.11 Authentication IPv6 Router Discovery 802.1X and EAP 802.11i 4-Way HS IPv6 DAD MIPv6 Home Reg MIPv6 RO Reg

24. Example: Improved Basic Flow

25. other node access network client home Beacon Beacon includes: - Access node identifier - Access network identifier - Possible other “advertised” information, such as capabilities, roaming partner identifiers, and so on

26. other node access network client home Secure Attachment Beacon The functions of the secure attachment protocol: - Authenticate the claimed identities (opportunistically) - Turn ciphering on, as in 802.11i 4-way handshake It also piggybacks the following: - Deliver IPv6 router advertisements - Authentication and authorization to the home (partially) - May perform address allocation on behalf of the client - May perform mobility registration on behalf of the client

27. other node access network client home Secure Attachment Beacon I1: trigger exchange --------------------------> select pre-computed R1 R1: puzzle, D-H, key, sig <------------------------- check sig remain stateless solve puzzle I2: solution, D-H, {key}, sig --------------------------> compute D-H check cookie check puzzle check sig R2: sig <-------------------------- check sig compute D-H

28. other node access network client home Beacon Secure Attachment Home auth & authz - The home authentication process follows the identity/challenge/response/success model (for instance) - A mobility protocol home registration is carried in the same messages -- executed after the final response message is sent

29. other node access network client home Beacon Secure Attachment Home auth & authz RO registration 1. Client delivers its public key, other parameters, and a statement that delegates the access network to allocate an address for it. 2. Access network has a statement from an authority about the prefixes it “owns”. It constructs an address and sends the address, the statement, and the client’s information to the home network. 3. Home network sends the information along to the correspondent node. Correspondent node believes the validity of the care-of address since it trusts the same authority. in a HIP-like mobility solution there is no need to verify the home address; client’s signed statement is sufficient.

30. Example: Variation with Better Mobility Support

31. other node access network client home Beacon Secure Attachment Home auth & authz RO registration Care-of Address Test Variation: A common authority can be avoided by a care-of address test.

32. Example: Handoffs

33. access network access node 1 client access node 2 Beacon Secure Attachment - Access node 1 has a signed statement from the access network that it is a part of the network. This is given to the client. - After authentication and authorization at the home network, a set of explicit authorization criteria are known. A signed statement is given to the client, saying that the client is allowed to move to another access node within the same network, as long as the criteria are fulfilled.

34. access network access node 1 client access node 2 Beacon Secure Attachment Secure Attachment - Access node 2 has a similar statement from the access network as well. - Client presents its statements and the usual home authentication/authorization process can be skipped. Client gets access. - However, access node 2 needs to verify authorization criteria. In many case this implies contacting a central node in the access network (e.g. concurrent usage limit).

35. Conclusions

36. Conclusions • Need to look at the whole problem • Measurements • System-level security story • Solutions • Some early solution ideas presented • Clearly more work is needed for the details, security analysis & actual benefits • Feedback appreciated!