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Anton Kozlov Mobile IP: Security Issues

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Anton Kozlov Mobile IP: Security Issues

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  1. Anton KozlovMobile IP: Security Issues Survey of security chapters from the book by James D. Solomon, Mobile IP: The Internet Unplugged, Prentice Hall, 1998 Applied Crypto and e-Security Lab http://www.cs.bu.edu/groups/aces/ Boston University 2000

  2. Current State of Mobile Computing • Mobile computers are one of the fastest growing segments of the PC market • Short-range wireless networks (Bluetooth) available from IBM, Toshiba, Dell, HP… • High-speed (11 Mbps) wireless LAN products are now easily and cheaply available (IEEE 802.11a, IEEE 802.11b) • Low speed (currently 128 Kbps) Metropolitan Area Wireless Network services are available in some cities and spreading (Metricom’s Ricochet) Applied Crypto and e-Security Lab Boston University 2000

  3. Mobile Computers’ Characteristics • May change point of network connection frequently • May be in use as point of network connection changes • Usually have less powerful CPU, less memory and disk space • Less secure physically • Limited battery power Applied Crypto and e-Security Lab Boston University 2000

  4. Wireless Networks’ Characteristics • Generally lower bandwidth • Higher latency and variability • Higher error rate • More susceptible to interference and eavesdropping Applied Crypto and e-Security Lab Boston University 2000

  5. Outline of the Tutorial • Part 1: The Need for Mobile IP • Part 2: Mobile IP Overview (for IPv4) • Part 3: Security Issues • A Simple Mobile IP Application (Private Network without Internet connection) • A More Complicated Application: Internet-Wide Mobility Applied Crypto and e-Security Lab Boston University 2000

  6. Part 1: The Need for Mobile IP • Problems • Terminology • What Happens When a Node Changes Link? • Can’t We Solve This Problem with Host- Specific Routes? • Why Not Just Change the Node’s IP Address? • Can’t We Just Solve the Problem at the Link Layer? • What If We Only Need Nomadicity? Applied Crypto and e-Security Lab Boston University 2000

  7. Mobile IP solves the following problems: • If node moves from one link to another without changing its IP address, it will be unable to receive packets at the new link • If a node changes its IP address when it moves, it will have to terminate and restart any ongoing communications each time it moves • Mobil IP solves these problems in secure, robust, and medium-independent manner whose scaling properties make it applicable throughout the entire Internet Applied Crypto and e-Security Lab Boston University 2000

  8. The Need for Mobile IP • Terminology • A home link is the link on which a specific node should be located; that is the link, which has been assigned the same network-prefix as the node’s IP address • A foreign linkis any link other than a node’s home link – that is, any link whose network-prefix differs from that of the node’s IP address • Host-specific route is a routing-table with Prefix-Length of 32 bits, it will provide a match for exactly one IP Destination Address; namely, the address specified in the Target field • Mobility is the ability of a node to change its point of attachment from one link to another while maintaining all existing communications and using the same IP address at its new link Applied Crypto and e-Security Lab Boston University 2000

  9. What Happens When a Node Changes Link? Applied Crypto and e-Security Lab Boston University 2000

  10. Can’t We Solve the Mobility Problem with Host-Specific Routes? • How Might Host-Specific Routes Solve the Problem? • If it Solves the Problem, Is This Solution a Good One? Applied Crypto and e-Security Lab Boston University 2000

  11. Is This Solution a Good One? • How Many Mobile Nodes We Can Expect? • How Many Routes Are Required for Each Mobile Node? • How Fast Will a Node Change Links? • Is This Solution Robust? • Is It Secure? Applied Crypto and e-Security Lab Boston University 2000

  12. Conclusion:Host Specific Routes is an Unworkable Solution to Node Mobility in the Internet • Minimally, host-specific routes must be propagated to all nodes along the path between a mobile node’s home link and its foreign link • Some (in the worst case all) of these routes must be updated every time the node moves from one link to another • We expect millions of nodes to be operating Applied Crypto and e-Security Lab Boston University 2000

  13. Host-Specific routing has severe scaling, robustness, and security problems • Unless host-specific routes are propagated to a much larger set of routers than minimal set described in the first item above, then the Internet mobility to route around isolated node and link failures is negated by host-specific routing • Serious security implications would require authentication, and complicated key management protocol to address Applied Crypto and e-Security Lab Boston University 2000

  14. Why Not Just Change the Node’s IP Address? • Can Connections Survive a Changing IP Address? • No, because all open TCP connections will be terminated • How Do We Find a Node Whose IP Address Keeps Changing? • Only if a mobile node itself initiates communication, a huge overhead to keep entries in DNS updated, address returned by a name server is subject to change at any moment • Can’t we just solve the problem at the Link Layer? (Cellular Digital Packet Data - CDPD (11Kbps), IEEE 802.11…) • Provides node mobility only in the context of a single type of medium and within a limited geographic area Applied Crypto and e-Security Lab Boston University 2000

  15. What If We Only Need Nomadicity? • A nomadic node is one which must terminate all existing communications before changing its point-of-attachment, but then can initiate new connections with a new IP address once it reaches its new location. • If all communications are initiated by the user of a mobile node, and the user does not mind shutting down his applications and restarting then at a new location, then nomadicity is indeed sufficient Applied Crypto and e-Security Lab Boston University 2000

  16. Why Mobility Is Preferable to Nomadicity? • Many applications have configuration data bases which depend on IP addresses, as opposed to host names • In the future Servers and not just Clients might need to become mobile (Clients know their Servers only by their IP addresses) • Some license application vendors provide network-licensing systems which restrict access to only those nodes possessing specific ranges of IP addresses • Some security mechanisms provide access privileges to nodes based upon their IP addresses. Mobile nodes employing Mobile IP allow such mechanisms to work in the presence of node mobility • Limited availability of IPv4 addresses, need for specific address assignment mechanisms Applied Crypto and e-Security Lab Boston University 2000

  17. Summary • A node that changes from one link to another is incapable of communicating at the new location unless it changes its IP address • Host-specific routing is not workable solution in the context of the global Internet • Changing a node’s IP address is undesirable • The difference between mobile and nomadic computing (impossible for other node to know at what address a nomadic computer can be reached at any given moment) Applied Crypto and e-Security Lab Boston University 2000

  18. Summary (cont.) • All link-layer solutions share limitations in their geographic applicability and the media over which they can run. • Even in those instances where a node requires only nomadicity, the more subtle advantages offered by Mobile IP mobility can make network administration much easier. Applied Crypto and e-Security Lab Boston University 2000

  19. Part 2: Mobile IP Overview (for IPv4) • Is Mobile IP an Official Standard? • What Is the Scope of the Mobile IP Solution? • What Are the Requirements for Mobile IP? • What Assumption Does Mobile IP Make? • Where Does Mobile IP Reside? • Generally How Does Mobile IP Works? • Summary Applied Crypto and e-Security Lab Boston University 2000

  20. Is Mobile IP an Official Standard? • Mobile IP was approved by the Internet Engineering Steering Group (IESG) in June 1996 and published as a Proposed Standard in November 1996. • Main reference document : Request for Comments (RFC) 2002 • There are other RFCs defining specific aspects of Mobile IP, such as tunneling, applicability, Management Information Base… Applied Crypto and e-Security Lab Boston University 2000

  21. What Is the Scope of the Mobile IP Solution? • Mobile IP is a network-layer solution to node mobility in the Internet • It accomplishes its task by setting up the routing tables in appropriate nodes, such that IP packets can be sent to mobile nodes not connected to their home link • Can be considered to be a routing protocol, which has a very specialized purpose of allowing IP packets to be routed to mobile nodes which could potentially change their location very rapidly. • Mobile IP is unique in its ability to accommodate heterogeneous mobility in addition to homogeneous mobility. • Solves the primary problem of routing IP packets to mobile nodes, which is a first step in providing mobility on the Internet. A complete mobility solution would involve enhancements to other layers of the protocol stack. Applied Crypto and e-Security Lab Boston University 2000

  22. What Are the Requirements for Mobile IP? • A mobile node must be able to communicate with other nodes after changing its link-layer point-of-attachment to the Internet • Must be able to communicate using its home (permanent) IP address, regardless of its current link-layer point-of-attachment to the Internet • Must be able to communicate with other computers that do not implement the Mobile IP mobility functions • The Mobile IP implementation should be limited only to the mobile nodes themselves and the few nodes which provide special routing functions on their behalf • Must not be exposed to any new security threats over and above those to which any fixed node on the Internet is exposed Applied Crypto and e-Security Lab Boston University 2000

  23. What Assumption Does Mobile IP Make? • Mobile IP’s fundamental assumption is that unicast packets – those destined to a single recipient – are routed without regard to their IP Source Address. • We will see how that assumption, though theoretically valid, might not be operationally valid under certain circumstances (Denial-of Service) Applied Crypto and e-Security Lab Boston University 2000

  24. Where Does Mobile IP Reside? • There are 3 functional entities where it is implemented: • Mobile Node – a node which can change its point-of-attachment to the Internet from one link to another while maintaining any ongoing communications and using its (permanent) IP home address • Home Agent – router with an interface on the mobile node’s home link, which: • Is informed by the mobile node about its current location, represented by its care-of-address • In some cases, advertises reachability to the network-prefix of the mobile node’s home address, thereby attracting IP packets that are destined to the mobile node’s home address • Intercepts packets destined to the mobile nodes home address and tunnels them to the mobile node’s current location, i.e. to the care-of-address Applied Crypto and e-Security Lab Boston University 2000

  25. Where Does Mobile IP Reside? • Foreign Agent – a router on a mobile node’s foreign link which: • Assists the mobile node in informing its home agent of its current care-of address • In some cases, provides a care-of address and de-tunnels packets for the mobile node that have been tunneled by its home agent • Serves as default router for packets generated by the mobile node while connected to this foreign link Applied Crypto and e-Security Lab Boston University 2000

  26. Mobile IP Entities and Relationships Applied Crypto and e-Security Lab Boston University 2000

  27. IP Tunneling • A tunnelis a path followed by a fist packet while it is encapsulated within the payload portion of a second packet: Applied Crypto and e-Security Lab Boston University 2000

  28. Properties of Care-of Address • A care-of address is an IP address associated with mobile node that is visiting a foreign link: • A care-of address is specific to the foreign link currently being visited by a mobile node • Generally changes every time the mobile node moves from one foreign link to another • No Mobile IP-specific procedures are needed in order to deliver packets to a care-of address • Is used as the exit-point of a tunnel from the home agent toward the mobile node • Is never returned by DNS when another node looks up the mobile node’s hostname Applied Crypto and e-Security Lab Boston University 2000

  29. Two Conceptual Types of Care-of Addresses • A foreign agent care-of address is an IP address of a foreign agent which has an interface on the foreign link being visited by a mobile node. Can be shared by many mobile nodes simultaneously • A collocated care-of address is an IP address temporarily assigned to an interface of the mobile node itself. The network-prefix of a collocated care-of address must equal the network-prefix that has been assigned to the foreign link being visited by a mobile node. This type of c/o address might be used by mobile node in situations where no foreign agents are available on a foreign link. A collocated c/o address can be used by only one mobile node at a time Applied Crypto and e-Security Lab Boston University 2000

  30. Applied Crypto and e-Security Lab Boston University 2000

  31. Generally How Does Mobile IP Works? • Home Agents and Foreign Agents advertise their presence on any attached links by periodically multicasting or broadcasting special Mobile IP messages called Agent Advertisements • Mobile Nodes listen to these Agent Advertisements and examine their contents to determine whether they are connected to their home link or a foreign link • A Mobile Node connected to a foreign link acquires a care-of address. A foreign agent care-of address can be read from one of the fields within the foreign agent’s Agent Advertisement. A collocated care-of address must be acquired by some assignment procedure, such as Dynamic Host Configuration Protocol (DHCP), the Point-to-Point Protocol’s IP Control Protocol (IPCP), or manual configuration Applied Crypto and e-Security Lab Boston University 2000

  32. How Does Mobile IP Works (cont.)? • The mobile IP Registers the care-of address acquired previously with its home agent, using a message-exchange defined by Mobile IP. It asks for service from a Foreign Agent, if one is present on the link. In order to prevent Denial-of-Service attacks, the registration messages are required to be authenticated • The Home Agent or some other router on the home link advertises reachability to the network-prefix of the Mobile Node’s home address, thus attracting packets that are destined to the Mobile Node’s home address. The Home Agent intercepts these packets, and tunnels them to the care-of address that the mobile node registered previously • At the care-of address – at either the Foreign Agent or one of the interfaces of the mobile node itself – the original packet is extracted from the tunnel and then delivered to the Mobile Node • In the reverse direction, packets sent by the Mobile Node are routed directly to their destination, without any need for tunneling. The Foreign Agent serves as a default router for all packets generated by visiting node Applied Crypto and e-Security Lab Boston University 2000

  33. Mobile IP Summary • Allows node mobility across media of similar or dissimilar types • Uses the Mobile Node’s permanenthome address when it changes its point of attachment to the Internet • Not requires any hardware and software upgrades to the existing, installed base of IPv4 hosts and routers – other than those nodes specifically involved in the provision of mobility services • Mobile Node must provide strong authentication when it informs its Home Agent of its current location • Uses tunneling to deliver packets that are destined to the Mobile Node’s home address • 3 main entities: Mobile Nodes, Foreign Agents and Home Agents • 3 basic functions: Agent Discovery, Registration, Packet Routing Applied Crypto and e-Security Lab Boston University 2000

  34. Part 3a. Security Issues: Simple Mobile IP Application (Intranet without connection to the Internet) • How is Mobile IP deployed? • Insider Attack • Mobile Node Denial-of-Service • Replay Attacks • Theft of Information: Passive Eavesdropping • Theft of Information: Session-Stealing (Takeover) Attack • Other Active Attacks Applied Crypto and e-Security Lab Boston University 2000

  35. How is Mobile IP Deployed? • All hosts are wholly owned by the enterprise • Each router performs both home agent and foreign agent functionality: Applied Crypto and e-Security Lab Boston University 2000

  36. Insider Attacks • Usually involve a disgruntled employee gaining access to sensitive data and then forwarding it to a competitor • Enforce strict control who can access what data • Use strong authentication of users and computers • Encrypt all data transfer on an end-to-end basis between the ultimate source and ultimate destination machines to prevent eavesdropping Applied Crypto and e-Security Lab Boston University 2000

  37. Mobile Node Denial-of-Service • A Bad guy sends a tremendous number of packets to a host (e.g., a Web server) that brings the host’ CPU to its knees. In the meantime, no useful information can be exchanged with the host while it is processing all of nuisance packets • A Bad Guy somehow interferes with the packets that are flowing between two nodes on the network. Generally speaking, the Bad Guy must be on the path between the two nodes on order to wreak any such havoc Applied Crypto and e-Security Lab Boston University 2000

  38. Denial-of-Service Attack • A Bad Guy generates a bogus Registration Request specifying his own IP address as the care-of address for a mobile node. All packets sent by correspondent nodes would be tunneled by the node’s home agent to the Bad Guy: Applied Crypto and e-Security Lab Boston University 2000

  39. How Does Mobile IP Prevents this Denial-of-Service Attack? • Note: In case of mobility a Bad Guy could attack from anywhere in the network, it does not have to be “on the way”. • Solution: to require cryptographically strong authentication in all registration messages exchanged by a mobile node and its home agent. • Mobile IP by default supports MD5 Message-Digest Algorithm (RFC 1321) that provides secret-key authentication and integrity checking Applied Crypto and e-Security Lab Boston University 2000

  40. Authentication of Registration Messages via Keyed MD5 • A mobile node generates a Registration Request, consisting of the fixed length portion and the Mobile-Home Authentication Extension, it fills in all the fields of the request and extension except for the Authenticator field. Then it computes 16-byte MD5 message digest over: the shared secret key, the fixed length portion, all extensions without Authenticator field, and the shared secret key again. The Mobile IP authentication extensions provide both authentication and integrity checking Applied Crypto and e-Security Lab Boston University 2000

  41. Replay Attacks • A Bad Guy could obtain a copy of a valid Registration Request, store it, and then “replay” it at a later time, thereby registering a bogus care-of address for the mobile node • To prevent that the Identification field is generated is a such a way as to allow the home agent to determine what the next value should be • In this way, the Bad Guy is thwarted because the Identification field in his stored Registration Request will be recognized as being out of date by the home agent (timestamps or nonces are used for Identification field) Applied Crypto and e-Security Lab Boston University 2000

  42. Summary • Mobile IP registration has has built-in prevention of denial-of-service attacks. Specifically, it is impossible for a Bad Guy to lie to a mobile node’s home agent about that mobile node’s current care-of address, because all registration messages provide authentication of the message’s source, integrity checking and replay protection Applied Crypto and e-Security Lab Boston University 2000

  43. Theft of Information: Passive Eavesdropping • Assumption: unauthorized persons will inevitably gain wired or wireless access to the network infrastructure • Use of Link-Layer Encryption • We also assume that key management for the encryption is performed without disclosing the keys to any unauthorized parties • Use of End-to-End Encryption (SSH, SSL…) Applied Crypto and e-Security Lab Boston University 2000

  44. End-to-End Encryption vs. Link Encryption • The Encapsulating Security Payload (RFC 1827) can provide end-to-end encryption to other application programs not supporting it themselves Applied Crypto and e-Security Lab Boston University 2000

  45. Theft of Information: Session-Stealing (Takeover) Attack • A Bad Guy waits for a legitimate node to authenticate itself and start an application session • Then it takes over the session by impersonating the identity of the legitimate node • Usually he must send a tremendous number of nuisance packets to the legitimate node in order to prevent it from realizing that its session was hijacked Applied Crypto and e-Security Lab Boston University 2000

  46. Session-Stealing on the Foreign Link • The Bad Guy waits for a mobile node to register with its home agent • The Bad Guy eavesdrops to see if the mobile node has any interesting conversation taking place (remote login session to another host, connection to the electronic mailbox) • The Bad Guy floods the mobile node with nuisance packets • The Bad Guy steals the session by sending the packets that appear to have come from the mobile node and by intercepting packets destined to the mobile node Applied Crypto and e-Security Lab Boston University 2000

  47. Session-Stealing Prevention • Same method as in the case of Passive Eavesdropping: • minimally link-layer encryption between the mobile node and the foreign agent (session-stealing on the foreign link) • With the preference of end-to-end encryption between the mobile node and its corresponding node (elsewhere) • Note: a good encryption scheme provides a method by which a decrypting node can determine whether the recovered plaintext is gibberish or whether it is legitimate (integrity checking) Applied Crypto and e-Security Lab Boston University 2000

  48. Other Active Attacks • The Bad Guy connects to the network jack, figures out he IP address to use, and tries to break to the other hosts on the network • He figures out the network-prefix that has been assigned to the link on which the network jacks connected • The Bad Guy guesses a host number to use, which combined with the network-prefix gives him an IP address to use on the current link • The Bad Guy proceeds to try to break into the hosts on the network guessing user-name/password pairs Applied Crypto and e-Security Lab Boston University 2000

  49. Protection against such attacks • All publicly accessible network jacks must connect to foreign agent that demands any nodes on the link to be registered (authenticated). • Remove all non-mobile nodes from the link and require all legitimate mobile nodes to use (minimally) link-layer encryption Applied Crypto and e-Security Lab Boston University 2000

  50. Summary: Intranet Model Security • We described a simple deployment of Mobile IP on individual corporate campus (intranet) • All of the routers were upgraded to be both home agents and foreign agents, all reasonably portable host were upgraded to mobile hosts • Home addresses were assigned according to the user’s department • Mobile IP authentication Keys were configured between the mobile nodes and their respective home agents • Assumed the existence of physical security flaws • Used link encryption over the foreign link to minimally protect the internal data, but generally preferred end-to-end encryption • Considered Denial-of Service attack in which a Bad Guy lie to a mobile node’s home agent about mobile node’s current care-of address • Showed how a combination of the Mobile-Home Authentication Extension and Identification field are designed to provide Authentication, Integrity Checking, and Replay Protection for all Registration Requests and Replies Applied Crypto and e-Security Lab Boston University 2000