1 dagstuhl dtn workshop 2005 delay tolerant networks - some thoughts about security hannes...
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1Dagstuhl DTN Workshop 2005
Delay Tolerant Networks-
Some Thoughts about Security
Hannes TschofenigThis presentation has been produced 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 presentation 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 presentation, which is merely representing the authors view.
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Acknowledgment
• Some slides are based on input and discussions with Jari Arkko and Pasi Eronen.
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Design Space Overview (1/2)
Wirelessnetwork
End-to-end Connectivity Available
M FInternet
Wirelessnetwork
Internet FIf
Intermediary peers to isolate the wireless link
Mobilenetwork
M Im
Wirelessnetwork
Internet FIf
End Host interacts with a proxy
M
Wirelessnetwork
End-to-end Store-and-Forward
M FInternet
I4
I3
I2
I1
Wirelessnetwork
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Calls for efficient mechanisms (roundtrip, bandwidth)
Design Space Overview (2/2)
• Solution affecting parts:– What are the devices that need to be signaled?– How many of them? (end hosts only vs. many nodes along the
path) – Where are they? What is the relationship between the end host
and these boxes?
• DTN Properties1. Possibly no e2e connectivity2. Long or variable delay3. Asymmetric data rates4. High error rates
See above-issues
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Security “Goals”
• Hop-by-Hop / End-to-middle– Prevent access by unauthorized applications– Prevent applications from asserting control over the DTN
infrastructure• End-to-End
– Typically very application dependent– Hard to accomplish and have different properties than
security offered to the middle of the network
• There are many other issues: – Network hiding, user identity confidentiality, privacy, DoS,
etc.
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Network Access Authentication and Authorization
a) Why existing network access auth/authz might not be appropriate for DTNsb) Can the result of network access authentication be helpful for the DTN architecture?c) Are the existing concepts useful for DTN?
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Some Current Problems 1
• DTN: Hosts might be partitioned in a number of connected clouds (possibly 1)
• Reasonable to consider the entire protocol stack rather than a single protocol (particular if performance is important)
• Attachments involve a large number of messages • Over 50% of this is due to security • Request/Response style, even across the Internet• Multiple mandatory waiting periods• Iteration over available accesses
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clientaccess
network homeothernode
Beacon
802.11 Attachment
802.11 Authentication
802.1X and EAP
802.11i 4-Way HS
IPv6 Router Discovery
IPv6 DAD
Nemo/MIPv6 Reg
MIPv6 RO Reg
Current Procedure(IPv6 + WLAN)
9Dagstuhl DTN Workshop 2005
Some Current Problems 2
• Limited information transfer & control–Network selection–Handoff guidance and control–Capabilities of a network not available to end host
• Limited business model support–No ad hoc, no credit card, –Real-time AAA interaction
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Fixing some selected aspects…
• Some EAP methods are quite inefficient
• Proposed alternatives:– EAP-PSK (lightweight symmetric mechanism)– EAP-IKEv2 (flexibility & efficiency)
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Today - Subscription-based Network Access
• Network Access based on trust relationship between MN<->AAAH, AAAH <-> AAAL• De facto keying architecture based on RADIUS/Diameter in relationship with EAP;
Authentication in real-time between MN<->AAAH;• Establishment of session keys is an important consideration for the architecture• NOT well suited for a certain DTN architectures
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Authorization
• Why do so many architectures require interaction with the “home network”/third party?– Authorization provided by the home network
(based on a dynamic set of attributes)• Credits, Number of concurrent sessions, Location• Attributes sent to the enforcement point (tunnel attributes, session
lifetime, keying material, etc.)
– Real-time interaction required to deal with pre-paid cards, accounting, credit checks, re-authorization
– Bootstrapping of keying material
• When is AAA alike interaction needed for applications? – Authorization decision different to network access authentication– When cleaner protocol separation is desired.
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Re-Thinking Authorization
• What would we like to accomplish?
– Fewer roundtrips and more efficiency (with existing architectures)
– Revised network access architecture – Avoid real-time interaction with home network
User NASNetworkAccessServer
AAAProxy
AAAServer
PPPIEEE
802.1X/.11i
IKEv2PANA
DIAMETER(RADIUS)
DIAMETER
Primary & SecondaryHome Servers
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Credential based Authorization
• Real-time interaction with the home network is not necessary if authorization decision can be computed locally.
• Example: – Authorization based on non-frequently
changing attributes (such as roles or traits)– Ability to regularly push revocation lists or
access control information to the enforcement points
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Example: Digital Coins
• Interaction between the Vendor and the TTP is still necessary to finally receive money.
• Smaller monetary amounts might justify batch transactions.
Challenge: Double Spending
(Tradeoff between taken risk and amount of required AAA interaction)
• Efficiency gain by using hash chains
• Pay-as-you-go scheme offers cost control and non-repudiation
User as Customer
Network as Vendor
Trusted Third Party
Trust based on prior agreement or contract
Dynamically established trust relationship
Long-lived or pre-established agreement
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Network Access Authentication and Relationship to other protocols
• Network Access Authentication authenticates and authorizes user at the home network.
• Protocol interaction is quite heavy-weight.
• Session keys are sent to the visited network
• A number of other protocols are used between the end host and the visited network (or related networks).
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Applicability of Bootstrapping
• How do you bind the initial authentication and authorization to a subsequent protocol interaction?
or• If you use other protocols do you again want to re-
run an EAP exchange back to the home network?
or• Would you like to use the initial authorization for
subsequent protocol interactions?
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EndHost
“Region” A
DTNGateway
DTNGateway
DTNGateway
“Region” BDTN
Gateway
DTNGateway
“Region” C EndHost
“Middlebox” Traversal
Which gateway should I use?
?DTN Gateway can be a DTN router, SIP proxy, performance enhancing proxy, HIP rendezvous server, NSIS node, etc..
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Again some things to think about…
• Discover middleboxes along the path dynamically?– Destination address based– Information within the request indicate the direction (impact on
forwarding) • Register with middlebox to accomplish global reachability? • Support mobility within one “region”?
– DTN gateway acts as a mobility anchor point.– Possibly in a nested fashion?
• Reuse existing [channel] security mechanisms (including DoS protection)?– DoS protection not possible with one-shot signaling messages
• Keep state at middleboxes to speed-up subsequent protocol interactions– Following the soft-state principle
• Use delegation to off-load tasks
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StrawmanEvaluate security of a “SIP-based” DTN
• Network Attachment– Security issues previously discussed
• Discovery of SIP-based DTN gateway:– Do you talk to a true gateway or just to the adversary? On path or not?
• Authentication and Authorization to SIP proxy– Traditional approach difficult (AAA infrastructure)– Trait-based authorization based on SAML could work
• Routing of SIP messages– DNS and/or DHT based => security
• End-to-end security guarantees– S/MIME ~ suffers from classical deployment problems
• Identifier (SIP URI) aspect requires further thoughts– Routing, anonymity, authorization, … (=> see next slides)
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The Identity of a Network
• DTN (region, entity)“Placing a DTN node in a particular region is an administrative decision, and may be influenced by differences in protocol families, connection dynamics, or administrative policies.” [draft-irtf-dtnrg-arch]
• Example: – {internet.icann.int, http://www.ietf.org}– Late binding approach / intentional naming
• Region seems to be used for routing only.– Aggregation capability assumes that there a structure in the identifier
• Related questions:– What do you actually authenticate/authorize?– Do you need to show that you belong to a certain network? – How do you join?– What happens if the prerequisites for adding a node to a ‘region’
change?
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Network IdentityFurther Examples• NEWARCH:
trust boundaries
• IPNL:Global/local address partitions
• NSIS NATFW NSLP:– Receiver behind a NAT wants to indicate that the signaling messages terminate at the outermost NAT (private
to public address space). – Same feature for a Firewall: Really difficult to say what the boundaries are.
• Ambient Networks project: – Idea: Explicit naming; cryptographic identifiers, if possible.
• SSID:– Most administrators of WLANs do not change the default SSID (see for example [Pri04] for a study about
WLAN usage in London where approximately 40% of the access points are running their default SSID.)– The SSID is non-unique network name that provides only minimal information relating to the network that the
STA may connect to.
• Adrangi-Network-Selection:– Identity selection hints to allow mediating network selection– A syntax by which mediating network information can be represented.
[Pri04] Priest, J.: "The State of Wireless London”, available at http://www.spacestudios.org.uk/content/articles/461.pdf, (July 2004), March 2004.
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Conclusion
• Delay Tolerant Networking means (like sensor networking) different things to different people.
• Different solution vary a lot depending on the chosen requirements
• Working on a security solution requires a good understanding of architecture and the assumptions
• Since many aspects seem to be highly application dependent it seems reasonable to investigate existing approach first.
• Good thing: – Pick an arbitrary security mechanism– Apply it to the DTN in your lab– It will just work fine