1. Routing Security in Ad Hoc Networks
Justin Lomheim
Shirshanka Das

2. Outline Ad Hoc Networks DSR Review AODV Review
Specific Attacks on DSR and AODV
ARAN Protocol (e.g. secure AODV)
Questions
References

3. Ad Hoc Networks infrastructureless
dynamic topologies (in mobile ad hoc nets)
variable capacity, limited bandwidth links
energy constrained operation
unicast, multicast, broadcast traffic
physical security considerations
currently AODV & DSR routing under consideration for IETF MANET specification

4. Ad Hoc On Demand Distance Vector (AODV) Review
distance vector algorithm using sequence numbers for updates (based on DSDV)
generates routes on-demand, reducing total number of broadcasts required
classified as a pure on-demand scheme, since nodes not involved in routing do not maintain routing info or participate in table exchanges

5. Dynamic Source Routing (DSR) Review
on-demand protocol based upon source routing
designed for scenarios where only a few source nodes flow to a few destination nodes
source and destination nodes gather routing info into caches, through exchange of flooded query and reply packets with full routing information
once discovered, routes are as needed until they fail due to lost message transmissions

6. AODV and DSR Route Discovery
No Route
To D !!
RREQ
RREQ
RREQ
RREP D
RREP
RREP S
RREP
RREQ
RREP I
RREQ
Cache Hit !!

7. AODV Link Failure Mgmt infinite metric assigned to broken links
if a node along a route moves, its upstream neighbor detects it and forwards a notification message (RREQ w/ infinite metric)
link breakage triggers notification back to users of formerly active links until source is reached, which may then re-initiate route discovery.

8. AODV versus DSR
Both use a similar mechanism of RREP , RREQ and route caching
AODV : maintains DV type next hop forwarding tables
DSR : relies on source routing

9. Specific Attacks on AODV & DSR
modification
sequence numbers
hop counts
source routes
tunneling
impersonation
fabrication
error messages
source routes (cache poisoning)
DoS
trivial DoS*

10. Modification of Sequence Numbers
In AODV
a malicious node may divert traffic through itself by advertising a route (via a RREP) with a much higher sequence number than actual RREP

11. Modification of Hop Counts
In AODV
since routing decisions can involve hop count metric, a malicious node can request the hop count to zero so make itself more likely to be chosen along the path to the destination
A selfish node could use a high hop count to ensure no one routes through it in case it wants to save power

12. Modification of Source Routes
In DSR
as packets are delivered, a malicious node can simply remove necessary source route entries in the packet header
malicious node can drop any error messages coming back along the path

13. Tunneling
Falsely
tunneled path M2 M1
Decap
Encap S D

14. Impersonation to create loopsD M B C E X

15. Impersonation to create loopsD M B C E X

16. Impersonation to create loopsD M B C E X

17. Impersonation to create loopsD B C E X M

18. Fabrication Attacks False route error messages in AODV and DSR
Route Cache poisoning

19. Challenges No centrally administered secure routers
No strict security policies
Highly dynamic nature of mobile ad hoc networks
Current ad hoc routing protocols trust all participating nodes

20. Problem Secure ad hoc routing protocols are difficult to design:
- Existing protocols are optimized to spread routing information quickly as the network changes
- Security mechanisms consume resources and can delay or even prevent successful exchanges of routing information

21. Specific attacks
Location disclosure: reveals information regarding the location of nodes, or the structure of the network
Black hole: an attacker advertises a zero metric for all destinations causing all nodes around it to route packets towards it
Replay attack: an attacker sends old advertisements to a node causing it to update its routing table with stale routes
Wormhole: an attacker records packets at one location in the network, and tunnels them to another location, routing can be disrupted when only routing control messages are tunneled

22. Requirements for a secure ad hoc routing protocol
Prevents the exploits discussed
Route signaling cannot be spoofed
Fabricated routing messages cannot be injected
Routing messages cannot be altered in transit except in accordance with the functionality of the routing protocol
Routing loops cannot be formed through malicious action
Routes cannot be redirected from the shortest path
Unauthorized nodes should be excluded from route computation and discovery
Network topology should not be exposed neither to adversaries not to authorized nodes

23. Authenticated Routing for Ad Hoc Networks (ARAN) Protocol
Effectively basic AODV, except route discovery/setup/maintenance are authenticated
Utilizes public-key cryptography to verify hop-by-hop all route request “RDP” & route reply “REP” packets
Eliminates most routing security problems except for tunneling & trivial DoS attacks

24. ARAN – Initial Setup Public Key A IP Address A Create Time Expiry Time
Signature by T
Certificate A
Certificate B
Certificate C
Certificate D
Initially each node has its own certificate produced by trusted certificate server T.
Each node also has a copy of T’s public key, so they can verify other certificates.
In our example, node A wants to get a route to node D. A B C D
Trusted certificate server T

25. ARAN – Route Discovery Initial RDP packet IP Address D Certificate A
Nonce A
Create Time
Signature by A
Initial RDP packet
RDP: A -> D
Node A generates a RDP request packet for node D. Node A includes its own certificate, and then signs the RDP packet with its private key. Node A then broadcasts this packet to its neighbors. Clearly each neighbor can verify the packet truly came from node A. A B C D

26. ARAN – Route Discovery Intermediate RDP Packet verified RDP: A -> D
Certificate B
Signature by B
RDP: A -> D
verified
Upon receipt of the RDP packet, node B first verifies the packet. If passes the test, then node B takes the packet, signs it, appends its certificate, and forwards it on to each of its neighbors. A B C D

27. ARAN – Route Discovery verified verified RDP: A -> D Signature by C
Certificate C
RDP: A -> D
verified
verified
Again, at each step along the RDP request path, we validate the previous node’s signature, remove the previous node’s certificate and signature, record the previous nodes IP addy (e.g. AODV reverse path), sign the original message contents, append our own certificate, and forward broadcast the message. A B C D

28. ARAN – Route Setup Initial REP packet *Replies to first RDP packet*
IP Address A
Certificate D
Nonce A
Create Time
Signature by D
Initial REP packet
REP: A->D
verified
verified
verified
Destination replies to first RDP packet received. Although this may not be shortest hop packet, it means RDPs don’t get modified en-route, allowing both signature process and avoiding hop count = 0 attacks by malicious nodes. Reply packet is effectively similar to initial RDP packet. A B C D
*Replies to first RDP packet*

29. ARAN – Route Setup Intermediate REP Packet verified verified verified
REP: A -> D
Signature by C
CertificateC
REP: A->D
verified
verified
verified
verified A B C D

30. ARAN – Route Setup verified verified verified verified verified
REP: A -> D
CertificateB
Signature by B
REP: A->D
verified
verified
verified
verified
verified A B C D

31. ARAN – Route Complete verified verified verified verified verifiedB C D

32. ARAN – Route Maintenance
IP Address A
IP Address D
Nonce C
Create Time
Certificate C
Signature by C
ERR: A->D
Potential problem: fabrication of ERR messages – at least malicious node cannot create ERR messages for other nodes. “A node that transmits a large number of ERR messages, whether the ERR messages are valid or fabricated, should be avoided.” A B C D
Link broken!

33. Questions
Conflict between small weight nodes, cryptography – is there any reason to implement ARAN?
Any way to avoid centralized trust certificate server T?
Key revocation issues…
Sensor network security?