“An Anonymous On-Demand Routing Protocol – ANODR”Students: Peggy LeeSurapong SomkaewTutors: Jiejun KongXiaoyan HongCourse: Computer Science 218 Fall 20031. IntroductionWhen deploying an ad-hoc, multi-hop, wireless network in a hostile environment,security measures must be employed to prevent intrusions and attacks from adversaries. Inhostile environment, enemies use every possible mechanism to gather as much information abouttheir opponents; they analyze network traffic, intercept packets, eavesdrop, etc. A covert missiondeploying ad-hoc, multi-hop wireless network may be compromised if nodes’ identities,locations, or movement patterns are discovered by the enemies. Hence, a routing protocol used inthis environment must achieve route anonymity and location privacy. Route anonymity preventsenemies from tracing packets back to the sources or destinations. Location privacy preventsadversaries from discovering nodes’ identities and locations. This paper presents an AnonymousOn-Demand Routing Protocol (ANODR), which is designed specifically for use in hostile/covertenvironment. 2. Current On-Demand Routing SchemesCurrently, there exist many on-demand routing schemes, such as Ad Hoc On-DemandDistance Vector (AODV) and Distance Source Routing (DSR). In term of security, reactiverouting schemes are more “covert” than proactive routing schemes. In proactive routing, everynode maintains a routing table; if a node is captured, enemies can learn the identities of all nodesinvolved in the mission. However, in reactive routing, routing information is set up on demand.Nevertheless, the current on-demand routing schemes do not provide sufficient securitymeasure. Adversaries can extract and learn about the covert mission by observing packet flowsor intercepting data packet. For example, by intercepting a data packet in DSR, adversaries canprecisely determine the identities of the source and destination by retrieving routing informationstored in the header of a data packet. Thus, DSR is very unsuitable for covert mission. AODV is a better routing scheme when compared to DSR because it does not storerouting information in the header of a data packet. Nevertheless, it is still not suitable for covertmission because identities, movement patterns, and locations of source and destination may beextracted by analyzing packet flows. For instance, collaborative eavesdroppers can combine theireavesdropped data, and analyze the forwarding chain to discover the identities of the source anddestination.Hence, a new routing protocol is needed for networks deployed in hostile environment.One such protocol is Anonymous On-Demand Routing protocol (ANODR). 2.1 Basic ConceptsANODR is an on-demand routing scheme that achieves anonymity and untraceability.ANODR set up routes on-demand between a source and destination based on the concept of“broadcast with trapdoor information”. This means that senders and receivers do not need toreveal their identities during wireless transmission; both can remain anonymous. Besidesensuring anonymity, ANODR adds route untraceability by using route pseudonym andneighborhood traffic mixing. Every node maintains route pseudonyms (as in virtual circuits);only local nodes involved in data transmission know the route pseudonyms. The mixing strategyuses dummy packets to achieve extra security measure; dummy packets are broadcasted toprevent packets from being traced.2.2 Routing ProcessLike most ad-hoc, on-demand routing scheme, ANODR performs anonymous routediscovery by using RREQ and RREP control packets. After anonymous route discovery, datapackets are forwarded anonymously from the source to the destination. The following sectionspresent ANODR in more detail.2.2.1 Anonymous Route discoveryWhen a source in ANODR wishes to establish an anonymous route to a destination, itinitiates anonymous route discovery by creating an RREQ packet, and broadcasts it locally to itsneighbors. The RREQ packet is assembled with the following format:<RREQ, seqnum, KT(dest, Kcom), Kcom(dest), pkone, TBO> seqnum is a globally unique sequence number KT is a shared TESLA secret key between the source and the destination. dest is a 128-bit special tag denoting the destination Kcom is a 128-bit random nonce used as commitment key between the source anddestination pkone is a one time public key for the current forwarder TBO (Trapdoor Boomerang Onion) is a cryptographic onion that is critical for routepseudonym establishmentThe source will occupy the RREQ field with an 8-bit value, which denotes this packet asa RREQ packet. Then, a globally unique sequence number is specified. Afterward, the sourcesets a global trapdoor through KT(dest, Kcom); this global trapdoor can only be opened by thedestination since only the destination knows the TESLA secret key used for decryption.Kcom(dest) is stored at every RREQ forwarding node, and will be used to check that the globaltrapdoor has been opened by the destination. Afterward, the source occupies pkone with its publickey. The field pkone adds untraceability to ANODR since it establishes local route pseudonyms ateach hop; this pseudonym is known only to the two nodes in that hop. Finally, it sets up its localtrapdoor by encrypting a random value that it will remember with its symmetric key. Thisencrypted value is stored in the TBO field of the RREQ packet. The following figure illustrates the route discovery process, and the local trapdoormechanism implemented by TBO:TBOA = KA(src)TBOA = KB(NB, KA(src))TBOA = Kc(Nc, KB(NB, KA(src)))TBOA = Kc(Nc, Kc(Nc, KB(NB, KA(src))))Figure 1: ANODR-TBO: Anonymous route discovery using Trapdoor Boomerang OnionWhen intermediate forwarding node X sees RREQ packet, it first checks to see if it hasalready broadcast another RREQ packet with the same sequence number. If it has, it will discardthe received RREQ packet. Otherwise, it will construct a new RREQ packet, and rebroadcast itlocally. The TBO of the old RREQ packet will be embedded with a random nonce Nx, andencrypted by a random symmetric key Kx. The forwarding node will remember both Nx and Kxso route verification (local trapdoor) can be performed when an RREP packet is
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