Secure Communication A View From The Transport Layer MANET and WSN

1. Secure CommunicationA View From The Transport LayerMANET and WSN

2. Overview • Transport Layer and Security Issues • Anonymity • E-mail • WSN and MANET • Traffic Analysis • DOS Attacks • flooding • de-synchronization • Summary • References

3. Transport Layer and Security Issues

4. Transport Layer Basics

5. Transport Layer - Security • Securing end-to-end communication • Keys distribution and use for secure communication • Anonymous communication • Preventing traffic analysis • Preventing DOS attacks

6. Mobile Sensor Networks - Basics • Security Constraints • Low Power • Limited processing power • Limited memory • Limited bandwidth

7. Keys • Base Station assigns keys • Symmetric Key Algorithms • Saves computation resources • Establishes trust with sensor nodes • Saves computation and power • Computing and exchanging keys • Base station transmits the keys directly to the node • Saves power

8. Anonymity E-mail

9. E-mail Anonymity • Untraceable E-mail • Untraceable Return Addresses • Digital Pseudonyms

10. E-Mail Anonymity - Untraceable • Using Public Key encryption • Uses • Elections • Part of an organization, but want identity kept secret (CIA)

11. E-Mail Anonymity - Untraceable • Additional computer called the “Mix” • Bob wants to send Alice an untraceable message. • Bob sends the message encrypted with Alice’s public key, encrypted again with the Mix’s public key: • Km(R1, Ka(R0, M), A)  Ka(R0,M),A • Mix decrypts, eliminates R1, and forwards the message to Alice.

12. E-Mail Anonymity - Untraceable • Mix hides the correspondences between items in its input and output. • Outputs in uniformly sized items in lexicographically ordered batches. • Ensures no duplicate output (would show a pattern to an eavesdropper) • make R a timestamp • change Mix’s keys

13. E-Mail Anonymity - Untraceable • Multiple Mix’s • Cascade encryptions • First Mix’s (M2) input: Km2(R2,Km1(R1,Ka(R0, M),A),Am1)  • First Mix’s output: Km1(R1,Ka(R0, M),A))  • Final Result: Ka(R0, M),A)

14. E-Mail Anonymity – Return Address • What if Alice wants to respond to Bob? He is anonymous! • Bob can sends his address, encrypted so that only the Mix can read, and deliver it. • Km(R1,Ab), Kb(R0,M)  Ab, R1(Kb(R0, M))

15. E-Mail Anonymity – Return Address • Mix can verify recipient received the message • Certified Mail Service • Last Mix sends back to Bob: • Alice’s address • Message itself • Each Mix may sign the receipt

16. E-Mail Anonymity • Preventing Traffic Analysis • Send same number of messages per each batch • Pro - Hides number of messages sent from Bob • Con - Uses resources (power, bandwidth) • Send same number of messages to subsets of participants • Pro - Hides number of messages Bob sends to Alice, and minimizes dummy messages • Con - Still uses resources for dummy messages

17. E-Mail Anonymity - Pseudonyms • Digital Pseudonym: • A public key used to verify signatures made by the anonymous holder of the corresponding private key. • Roster: • List of pseudonyms kept by a trusted authority • Uses: • Elections – Roster of eligible voters

18. E-mail Anonymity – Pros & Cons • Pros: • Ability to be anonymous • Verified message delivery • Cons: • Additional hardware (mix) • What if you want to know the addressee (threat) • Trusted Authority • who and what determines this • Lots of additional encryption (time and resources)

19. Anonymity –MANET and WNS

20. Anonymity – Why • If an attacker can ID a node, and eavesdrop on traffic, they may be able to identify actual network traffic patterns. • Track a moving node • Identify what network a node belongs in

21. Anonymity – Cont. Wired connections with dedicated links Wireless connections with shared media • Wireless communication broadcast property makes it hard to see where where a node is, but makes it easier to eavesdrop. [picture - 11]

22. Anonymity – How • We will analyze how to achieve anonymity in both: • MANET • Mix-net • WNS • Anonymity done through preventing traffic analysis attacks

23. Anonymity - MANET • Similar to e-mail, uses Mix’s • A Mix-Net example in MANET [2]

24. Anonymity - MANET • Encryption and decryption of messages is the same as used with Mix’s in e-mail: • Multiple Mix’s • Cascade encryptions • First Mix’s (M2) input: Km2(R2,Km1(R1,Ka(R0, M),A),Am1)  • First Mix’s output: Km1(R1,Ka(R0, M),A))  • Final Result: Ka(R0, M),A)

25. Anonymity - MANET • Mix Advertisement • Sends message “I’m here” • Non-Mix node hears this and determine a dominant Mix-node • If it doesn’t hear an advertisement message from it’s Mix in some interval of time, it finds another Mix. • Mix Route Discovery and Update • Sender node (S) sends RREQ message to destination node (D)

26. Anonymity - MANET • Mix Route Discovery and Update • RREQ Phase: Sender node (S) sends RREQ message to destination node (D) • DREG Phase: D knows it is part of end-to-end communication, registers with it’s closest Dominator Mix • RUPD Phase: Mix broadcasts RUPD messages to nodes with a list of nodes registered to the Mix

27. Anonymity - MANET • Broadcasted RUPD Messages [2]

28. Anonymity - MANET • Potential security problem: • An attacker could hear S send a RREQ message, then hear D send a DREG message shortly after. • Solution: • S can send dummy RREQ messages to itself, to hide the real RREQ message to D

29. Anonymity - MANET • Pros: • Compromised node in the middle of the route does not reveal source or destination nodes • Dominant Mix could hide identity of S • Mix can also aide in preventing traffic analysis • Cons: • Additional hardware: Mix’s • Additional encryption

30. Anonymity – MANET - PPCS • PPCS – Privacy Preserving Communication • Three mechanisms: • Dynamic Flow Identification • Random Node Identification • Resilient Packet Forwarding

31. Anonymity – MANET - PPCS • Dynamic Flow Identification • Two flow pseudonyms, Pdi, Psi are defined for the forward and backward flows • Replaces the source and destination addresses • Source broadcasts RREQ packet containing these pseudonyms <RREQ, Psi, Pdi, Ksd(m)> • Intermediate nodes receive and try to decrypt Psd • “Trap door check”

32. Anonymity – MANET - PPCS • Random Node Identification • Dissociates a real node identifier from location information • RNI – random node identifiers

33. Anonymity – MANET - PPCS • Resilient Packet Forwarding • Multi-path random forwarding (MPRF) • Provides protection against traffic analysis • Helps avoid traffic congestion • Intermediate nodes randomly selects the next hop by it’s local list of possible next hop nodes.

34. Anonymity – MANET - PPCS • Potential problems: • Message could be followed from end-to-end • Solution: Encrypt again between intermediate nodes • Pros: • Node anonymity established • Cons: • More difficult to implement • Each intermediate node must look at the Psd of a RREQ message

35. Anonymity - WSN • Base Station ID hidden • Could take out entire network • How: • Hide which node is the base station by limiting traffic analysis

36. Anonymity - Summary • Some situations may require node anonymity • Ex: Election, CIA • E-mail anonymity • Mix • MANET and WSN anonymity • Mix and routing • Traffic Analysis

37. Preventing Traffic Analysis

38. Preventing Traffic Analysis – Why • High traffic and/or traffic patterns could indicate a base node/station • Base Node/Station • Entire network depends on it • Ex: Military • Determine critical nodes , chain of command • Forthcoming action • State change or network alertness

39. Traffic Analysis – Example Data traffic patterns using shortest path routing [7]

40. Traffic Analysis – Two Classes • Two classes of traffic analysis 1.) Rate Monitoring Attack– monitor packet sending rate 2.) Time Correlation Attack – deduce path by listening to nodes forward packets

41. Preventing Traffic Analysis – How • Multiple parent routing • Rate monitoring attacks • Controlled random walk • Rate monitoring attacks • Random fake paths • Time correlation attacks • Multiple, random areas of high communication activity • Rate Monitoring Attacks

42. Multi-Parent Routing • Reduces effectiveness of rate-monitoring attacks • Each node has multiple parents • Randomly select one parent each time it forwards a packet • Any level higher is a parent or • Record beacons as parents • Problems: • Does not eliminate rate-monitoring attacks • Still subject to time-correlation attacks

43. Multi-Parent Routing Multi-parent routing for node “u”

44. Random Walk • Reduces rate monitoring attack effectiveness • Forwarding packets: • To parent with probability of p • To neighbor with probability of (1-p) • Problems: • Still vulnerable to time correlation attack • Longer route consumes more energy (more hops to base station)

45. Random Fake Paths • AKA Fractal Propagation • Makes time-correlation attacks less effective • Fake packets are created and propagated through the network • Fake packets have a TTL parameter, K

46. Random Fake Paths Cont. • When a node receives a fake packet, it • decrements TTL (if zero, it drops the packet) • forwards the packet to a neighbor node • If a node hears it’s neighbor transmitting a fake packet with a TTL of k : • generates and forwards another fake packet • TTL = k-1 • probability

47. Random Fake Paths Cont. • Problems: • Already limited power is used on fake transmissions • Does not completely eliminate time correlation attacks • Generates a large amount of traffic by base station • If transmitting real packets more frequently, reduce the probability of sending a fake packet

48. Multiple, random areas of high communication activity • AKA Hot Spots • Makes rate monitoring more difficult • Node keeps track of which neighbors it sends fake messages to. • All neighbors start with the same probability of receiving a fake message from me • If I send a fake message to neighbor A, I increase the probability I send another fake message to it

49. Multiple, random areas of high communication activity – Cont. • Ability to create and destroy hotspots • Problems: • Does not eliminate rate monitoring, but does make an attacker waist time with a hotspot

50. Traffic Analysis - Summary