Security in Pervasive Wireless Security in Pervasive Wireless Systems Systems Wade Trappe
Breaking Down the Issues (summary) Breaking Down the Issues (summary) Wireless is easy to sniff. We still need encryption services and key management. Key Confidentiality freshness is an issue. Wireless hardware/equipment need to be safe from modification. Data/control info should not Integrity be modified before or during transit. Wireless networks will be the platform of choice for attacks. Should the network keep track of Forensics forensic evidence? Perpetual connectivity can mean constant surveillance! With snooping one can monitor Privacy mobility and handoffs between networks. Location is a new form of information provided by wireless systems that will facilitate new Location services. Location information needs to be trusted. The pervasiveness of the wireless networks should not mean that just anyone can participate! Intrusion Example: Rogue APs The value of a wireless network is its promise of ubiquitous connectivity. Unfortunately, Availability wireless networks are easy to “break” (e.g. jam, denial of service) RF energy radiates, and wireless entities within the radio coverage pattern may serve as Non-repudiation witnesses for the actions of the transmitter. WINLAB
Security Via Lower Layer Enforcements: Wireless Security Security Via Lower Layer Enforcements: Wireless Security at the Physical Layer at the Physical Layer � Wireless channels are “open” and hence more susceptible to eavesdropping, intrusion and spoofing… � Interestingly, wireless channel properties (“RF signatures”) can be exploited for authentication and to identify attackers � Project on protocols and algorithms for security functions; also experimental validation WINLAB
Secret key extraction from a wireless channel Secret key extraction from a wireless channel � Use channel reciprocity to build highly correlated data sets – Probe the channel in each direction – Estimate channel using recd. probe � Eve receives only uncorrelated information as she is more than λ /2 away � Level crossings are used to generate bits � Alice and Bob must exchange msgs over public channel to create identical bits � What if channel is not already authenticated? – Requires additional sophistry to prevent man-in-the-middle attack. – It is possible using the correlated data collected from received P R O B E probes. B E O P R P R O B E Get channel Positive excursion estimates L o c a t i o n s o f e x c u r s i o n s n t m e e g r e a i n n s o a t i o c L Negative excursion WINLAB Key Key
System Validation using 802.11 System Validation using 802.11 Alice � Eve Bob � Eve � Experimental setup: – Alice = AP – Bob = Client – Eve = Client on same channel Alice � Bob: PING REQUEST Bob � � Alice: PING REPLY � 20 packets per second Alice � Bob � Eve overhears packets from both legitimate users Bob � Alice (RSSI, timestamp) from recd. packet � headers are pulled out by each user � Mesg. exchange protocol uses the locations of excursions to distil identical bits � ~1 bit/sec in typical indoor environments Alice � Bob with no errors. WINLAB Bob � Alice
Defenses for Attacks of Radio Interference in Wireless Networks Defenses for Attacks of Radio Interference in Wireless Networks � Goal: to maintain wireless network connectivity in the presence of wireless interference (i.e. jamming) � Strategies: – Channel Surfing: Adapt network channel allocations in an on-demand manner – Spatial Retreats: Use mobility to evade interference sources and re-establish network connectivity – Anti-jamming Timing Channels: Failed packet reception events may be modulated to establish a low-rate jamming resistant communication channel – Radio Teaming: A team of transmitters exploits multipath environments to perturb angular receiver patterns, in spite of SINR levels of -10dB or worse. (Effect of a jammer on a network of Chipcon 1100 Radios) (Channel Surfing adjusts channels to re-establishes the network) WINLAB
Jamming- -Resistant Timing Channel Overlay Networks Resistant Timing Channel Overlay Networks Jamming � Objective: � Objective: – Create a – Create a low bit low bit- -rate overlay rate overlay that exists on that exists on Overlay Authent. Overlay Authent. Overlay Authent. Overlay Authent. Network Network Network Network the conventional physical/link- -layers layers in spite in spite the conventional physical/link Error Correct Error Correct Error Correct Error Correct 4Oz Overlay 4Oz Overlay 4Oz Overlay 4Oz Overlay of a broadband interferer. a broadband interferer. Overlay Framing Overlay Framing Overlay Framing Overlay Framing of Datalink Datalink Virtual Bitpipe Virtual Bitpipe Virtual Bitpipe Virtual Bitpipe Datalink Datalink Physical Physical Timing channel Timing channel Timing channel Timing channel Physical Physical � � Approach: Modulate the interarrival Approach: Modulate the interarrival time time between packet transmissions to convey between packet transmissions to convey information information Sender Sender Receiver Receiver The Timing Channel Overlay – Jammed packets are detectable Jammed packets are detectable – τ 1 τ 2 τ 3 τ 4 τ i …… t1 t2 t3 t4 t5 t i t i+ 1 tim e WINLAB
Cognitive Radio (CR) Cognitive Radio (CR) Expose the lower-layers of the protocol stack to researchers, developers and the “ public ” � – scan the available spectrum, select from a wide range of operating frequencies – adjust modulation waveforms, perform adaptive resource allocation � An ideal platform for abuse since the lowest layers of the wireless protocol stack are accessible to programmers . Poor programming: 1. 1. CR protocols will be complex, it will be easy to write buggy implementations 2. Runaway software processes… Greedy exploitation: 2. � Decrease back-off window in an 802.11 (or comparable) implementation � Ignore fairness in spectrum etiquette (many co-existence protocols assume honest participants, or honest data) Simply Ignoring Etiquette 3. � Primary user returns… so-what??? Economic/Game-theoretic Models 4. � Standard economic models for spectrum sharing seek to support cooperation– but cooperation does not ensure trusted operation! � Security is an anti-social topic! WINLAB
TRIESTE: T Trusted rusted R Radio adio I Infrastructures for nfrastructures for E Enforcing nforcing TRIESTE: Spec pecT Trum rum E Etiquettes tiquettes S � Goal: to regulate the future radio environment, ensure trustworthy cognitive radio operation How — two complementary mechanisms � – On-board enforcement – restrict any violation attempt from accessing the radio: � Each CR runs its ow n suite of spectrum etiquette protocols � Onboard policy checking verifies actions occur according to “ spectrum law s ” – An external monitoring infrastructure: � Distributed Spectrum Authority (DSA) — police agent observes the radio environm ent � DSA w ill punish CRs if violations are detected via authenticated kill com m ands. WINLAB
Security in MANETs MANETs: Attacks on AODV Routing : Attacks on AODV Routing Security in 3 → 1 M E C S D A B � Attacks on AODV – Forge RREQs/RREPs/RERRs on behalf of other nodes – Reduce the hop count in RREQs/RREPs – Increase the originator sequence number in RREQs – Increase the destination sequence number in RREPs – Selectively forward/reply RREQs, RREPs, and RERRs – Wormhole Attacks WINLAB
SEAR: Secure Efficient Ad hoc Routing Protocol SEAR: Secure Efficient Ad hoc Routing Protocol m+1 m+1 Seq#2 Seq#3 Seq#0 Seq#1 , …, h n-m-2 , h n-m-1 h 0 ,h 1 …,h n-2m-1 , h n-m ,h n-m+1 … ,h n-1 , h n Generation For RERRs Hop0 Hop1 � Characteristics – Authenticate RREQs/RREPs/RERRs – Based on symmetric key cryptography – Public key cryptography is only used in initial bootstrap phase – Sequence #’s and hop counts are protected through the use of a one-way function – Route errors are protected through a variation of TESLA � Each node maintains 2 hash chains for itself to use – Authenticator hash chain – TESLA key chain � Authenticator Hash Chain: What will basically happen is… – Each individual hop for each even sequence number should have a corresponding hash value – Odd sequence number only needs one hash value – Nodes who have an even sequence number have the corresponding next higher odd sequence number – Intermediate nodes cannot increase the sequence number or decrease the hop count WINLAB
SEAR Route Discovery SEAR Route Discovery � Route Request – RREQ: {S, D, ID, SrcNum, DstNum, Hop} – ID is redundant � Notation – Let v s,j,c denote authenticator for node S with sequence number j and hop count c – Assume the next even sequence number of S is 2i – The most recent destination sequence number known by S is j with hop count c � Details – Route freshness{S, SrcNum} – Originator broadcasts new RREQ: � {S, D, ID, 2i, v s,2i,0 , j, v d,j,c , 0, HERR} – Each neighbor checks the authenticators and applies a one-way function. Then broadcasts � If has a larger destination sequence num ber j’ w ith hop count c’ {S, D, ID, 2i, v s,2i,1 , j ’ , v d,j ’ ,c ’ , 1, HERR ’ } � � Otherw ise, {S, D, ID, 2i, v s,2i,1 , j, v d,j,c , 1, HERR ’ } � WINLAB
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