A security policy framework for eEnabled fleets and airports

A security policy framework for eEnabled fleets and airports
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    1 A Security Policy Framework for eEnabled Fleets andAirports Mirko Montanari, Roy H. CampbellUniversity of Illinois at Urbana-Champaign{mmontan2, rhc}@illinois.eduKrishna Sampigethaya, Mingyan LiBoeing Research & Development{radhakrishna.g.sampigethaya,}  Abstract—  The future airport is predicted to be a highly net-centric system-of-systems with advanced networking andwireless technology to accommodate the “eEnabledaircraft,” enhanced surface area operations, as well asgrowing business and societal demands. In this paper, we present a classification of security policies that need to beenforced in such modern airport systems. We propose adistributed architecture for policy-compliance monitoringthat enables runtime verification of compliance in the multi-organization environments typical of large-scaleinfrastructure systems. Compared to current solutions, our monitoring architecture allows each organization to acquireindependently information about the state of theinfrastructure while respecting integrity, confidentiality, andseparation-of-duty constraints that arise because of theinteraction between parts of the infrastructure managed bydifferent organizations 12 . T ABLE OF C ONTENTS  1.   I NTRODUCTION ................................................................. 1  2.   R  ELATED W ORK  ............................................................... 2  3. E -E NABLED F LEETS AND A IRPORTS ................................ 2  4.   F ORMALIZATION OF P OLICIES ........................................ 4  5.   M ULTI - ORGANIZATION POLICY COMPLIANCE ................ 6  6.   E VALUATION ..................................................................... 8  7.   C ONCLUSIONS ................................................................... 9  R  EFERENCES ......................................................................... 9  A PPENDIX A:   E XAMPLES OF S ECURITY P OLICIES ............ 10  B IOGRAPHY ........................................................................ 11  A CKNOWLEDGEMENTS ...................................................... 11    1.   I NTRODUCTION   A recent vision in commercial aviation is the “e-Enabledaircraft” that operates as an intelligent, mobile node in theInternet [1]. Safety, security, environmental, efficiency andeconomic benefits are provided to airlines, crew, ground personnel, passengers and business stakeholders. The performance of future eEnabled fleets, however, depends onthe correct operation of network services provided byairport infrastructure [2]. As the complexity of airportinfrastructure increases and changes become more frequent,manual control and operation become ineffective.Unintended or malicious changes in the configuration of a 1 978-1-4244-7351-9/11/$26.00 ©2011 IEEE 2 IEEEAC paper#1377, Version 5, Updated 2011:01:11 single system could introduce errors in the overallinfrastructure configuration that might remain invisible anddegrade or disrupt operations (e.g., [3]). Hence, for  preserving performance gains of e-Enabling, such errorsmust be timely detected to prevent systems from operatingin insecure or inefficient states.In this paper, we focus on the problem of monitoring airportinfrastructure operations to detect policy violations. Policies provide an efficient way to manage the operation of theairport infrastructure: each policy describes a portion of thecorrect operation state. When the system is operatingoutside the states specified by the policy, the system is potentially exposed to security problems and inefficienciesthat should be corrected quickly. For example, a policy maymandate that aircraft must land (i.e., weight-on-wheels) andthen access a remote airline system on the Internet for software update. If the aircraft accesses airline system before landing, then unwarranted aircraft safety concernsemerge about potentially malicious software updates or  potential exposure of flight-critical systems to unauthorizedexternal access. On the other hand, if the aircraft does notaccess the airline system even after landing, the error condition may create an undesirable delay in gate turn-around time for software refresh. Another policy mayspecify that maintenance devices must be disconnected fromInternet when accessing airplane systems to avoid acting asunintentional stepping-stones for threats. While a dedicatedmonitoring infrastructure could be developed for each policy, such an approach may prove expensive and notscalable given size and frequency of policy modifications.The proposed online policy monitoring system for airportinfrastructure addresses the scalability problem by providinga general framework for acquiring information aboutinfrastructure state at runtime and checking if the currentsituation is in violation of policies that governinfrastructure. However, since systems in airportinfrastructure are typically owned and controlled bymultiple organizations, such a monitoring system is facedwith several challenges in the design of the architecture andin the selection of the devices to use for acquiringinformation. First, each organization must enforce policiesindependently. Second, the validation of a policy mightrequire acquiring information about parts of theinfrastructure managed by a different organization. Thiscreates integrity and confidentiality problems, as businessconflicts between competing organizations might create    2reticence in sharing information or in relying on externalinformation for analysis. Third, to protect against sabotage,malicious employees, and device errors, critical informationfor the analysis should be acquired redundantly and in waysthat do not allow a single entity to corrupt all informationsources (i.e., separation-of-duty constraints).The contribution of this paper is two-fold. First, we presenta classification of security policies for monitoringinteractions between e-Enabled fleets, maintenance personnel and airport infrastructure. To our best knowledge,it is the first paper to establish the security policyframework for future eEnabled fleets and airports. Second,we present a system architecture that allows eachorganization to monitor the infrastructure independently.Our architecture is based on an algorithm that enables eachorganization to collect efficiently state information whilerespecting integrity, confidentiality, and separation-of-dutyconstraints that need to be enforced for the deployment of such monitoring in a multi-organization scenario.The rest of the paper is organized as follows. Section 2 provides an overview of related work in the area of policyverification. Section 3 describes the infrastructure of modern airports considered and the type of policies thatneed to be defined in such environments. Section 4 providesa framework for formalizing such policies. Section 5addresses the problem of multi-organization validation of  policies. Section 6 describes our experimental results, andSection 7 concludes our work. 2.   R  ELATED W ORK    Airport environment policy definitions have encompassedrules that regulate the use of runways by different types of aircraft [4]. In this work we provide a more generalframework for the definition of policies that integrate thenetwork infrastructure of the airport.The problem of acquiring information about network infrastructure has been previously addressed by systemssuch as NetQuery [5] and standards such as WBEM [6].However, none of the previous approaches is able toautomatically deal with complex multi-organizationconstraints such as replication and separation of duty.Other work addressed the problem of detecting potentialsecurity problems present in a system configuration. Nessus[7], TVA [8], and Mulval [9] are systems proposed for detecting the security consequences of erroneousconfiguration of infrastructure. The focus of this paper is onhow the information about the state of the infrastructure can be acquired so that it can be analyzed with the use of suchtechniques. 3. E -E NABLED F LEETS AND A IRPORTS   The network infrastructure of airports supports severalapplications, from interconnecting devices at check-in desksand gates to supporting the communication between aircraftand airline systems. In this work, we focus on theinteractions between e-Enabled fleets, maintenance personnel, and airport infrastructure services. Figure 1 provides an abstract view of the system architecture that weconsider representative of the e-Enabled airline system Figure 1: Architecture of the infrastructure of a future airport system.    3architecture at airports [10]. To support the maintenance of the e-Enabled fleet, four classes of devices interact in theairport infrastructure:(1)    Aircraft Hardware Maintenance: Portable deviceslocated on the tarmac that access aircraft systems to perform net-enabled operations (e.g., hardwareinspection/repair, sensor readings). These typically belong to organizations that are leased or owned byairlines.   (2)   Connectivity: Fixed wireless/wired network access points (e.g., WiFi, WiMAX, cellular, and power line)that interconnect e-Enabled aircraft with off-boardsystems on the Internet. These typically are owned bythird party service providers.(3)    Airline Maintenance Applications: Portable devicesthat are used in the cabin and gate to communicatedirectly with aircraft systems for airline maintenanceapplications (e.g., software update, cabin access).These are typically owned/leased by the airlines.   (4)   Tarmac Security Monitoring: Physical securityservices provided by CCTV camera, automatic door locks, and emergency devices. These are typicallyowned by the airport authority.For supporting maintenance, we consider crew devices that(i) maintain the aircraft RFID-tagged hardware; (ii) managesoftware, and multimedia; and (iii) manage gates andcontrol access to the aircraft cabins. Additionally, our system model considers other IT infrastructure that interactswith these devices. We include the interfaces with airline back-office servers that reside remotely and provideinformation, software and multimedia for the airline fleet.Security monitoring includes all physical security devicessuch as cameras or devices that enforce crew access controlin restricted areas of / around the aircraft. Such devicescommunicate using the network infrastructure provided bythe airport.The online validation of compliance requires a device toshare information about its state with the rest of theinfrastructure. We assume that each device allows access toa portion of the system’s state that it can “observe”, i.e., thatit can acquire because of its function. In this paper we focuson which information should be shared and not on how theinformation is shared by each device, as there are existingtechnologies through which devices can share informationabout the state. Network management systems, such asWBEM [6], allow information about the current state of thedevice to be queried from the network. Alternatively, secureintrospection techniques [11, 12] can be used to monitor thestate of a device in a way that is resilient to   compromises.Moreover, it is possible for developers to integrate thesecapabilities in their software and allow authorized third party to obtain information about the system’s state throughapplication-dependent protocols.We consider an adversary whose objective is lowering the performance gains of the e-Enabled aircrafts and airportsystems by exploiting vulnerabilities in the policymonitoring system. The adversary attempts to provide falsestate information to the policy monitoring system so that policy violations are not detected (i.e., false negative), or false policy violation notifications are generated (i.e., false positive). The adversary can compromise a limited number of devices in the infrastructure, i.e., using a set of validcredentials (e.g., malicious insider), or by exploitingvulnerabilities in the devices. We assume that the adversaryis not able to compromise a majority of devices that are partof the same redundant set used for policy validation (i.e., thesame vulnerability is not present on the majority of devicesthat provide a critical piece of information about the state).For non-critical policies, however, we assume devices reporttheir state information correctly, thereby considering threatsonly from unintentional misconfigurations and failures. 3.1.   S ECURITY P OLICIES FOR E -E NABLING The interactions between airport infrastructure, maintenancedevices, and e-Enabled aircraft fleets create a complexsystem composed of hundreds of elements. Thisinfrastructure needs to operate correctly to provide theservices that maintain the airport and keep the aircraft   operational. To enable a synergetic interaction between thedifferent parts and to establish security requirements,organizations use security policies that define the correctconfiguration of each component and define the actions thatare permitted by each user or device. While compliance to policies cannot guarantee perfect security, security policies provide a basic level of assurance against attacks that would be avoidable had proper security measures been taken.For example, a security policy for e-Enabled aircraft mightmandate that they must communicate with the groundsystems to check for new updates, but only upon landing. Not performing this check before landing could be potentially a sign of other malfunctioning. It could potentially introduce malicious updates or delay theapplication of important updates. Similarly, a security policy might specify that maintenance devices be authorizedto access the aircraft systems only if physically located onthe runway near the plane.   In the definition of security policies for airports, we canclassify policies in several classes based on the objective asfollows:(1)   Safety Related: These are used to ensure safe andregulated operation of aircraft.(2)    Access Control Related: These are used to preventunauthorized crew and device access to aircraftsystems.(3)    Business Related: These are used to securely minimizeoperational costs of aircraft and ensure quality of network connections.    4(4)    Airport Operation Related: These are used to securelyenable efficient allocation and ensure 24/7 availabilityof resources at the airport.Policies can be defined on each type of service provided byaircraft or ground systems.The definition of proper policies for the operation of theinfrastructure is critically important. Even if policies arecurrently defined by several organizations for different partsof the airport infrastructure, policies are yet to be fullydefined for regulating secure interactions between airportground systems and e-Enabled aircraft.Appendix A provides several examples the type of policiesthat need to be defined in each policy class. Note thatseveral of these requirements are theoretical and formulatedfor use only in our research. For the rest of the paper wefocus on three examples as representative policies for thedifferent policy classes:   (2) Aircraft accessing a “ground-only” airline applicationmust be in weight-on-wheels condition.(5) Maintenance device must be disconnected from the Internet when accessing aircraft systems.(11) Aircraft must automatically choose the most cost-effective wireless data link available that satisfies theminimum bandwidth requirement. Infrastructure systems have mechanisms for enforcing theconditions specified in the policies. However, for multiplereasons the enforcement of policies might fail: softwareerrors, hardware failures, or incorrect configurations mightallow the system to reach a state that violates the policy. Inthis case, it is important to have a system that is able todetect such violations and notify the situation for rectification. Additionally, reliable logging of violations isessential to provide evidence of compliance to policies. Toaddress these issues, we develop automatic methods for identifying when the infrastructure operates outside theconditions specified by the policy, while the process of acquiring information about the infrastructure state respectsthe confidentiality and integrity requirements posed by eachorganization. 4.   F ORMALIZATION OF P OLICIES   Automatic detection of policy violations is impossiblewithout knowing exactly which situations are considered policy compliant and which are not. To specify policieswithout ambiguities, it is necessary to express them in aformal language. Given its flexibility and expressiveness,we use the Datalog language [13]. This language has beenused in previous work for the specification of access control policies [14] and security of network infrastructure [9]. In particular, we represent the state of the system using theRDF language [15] and we represent policies usinginference rules [16].Using RDF, each entity in the system is identified by aunique string called URI. For example, we identify the firstrunway of the SEATAC airport using . Note that the URI isinterpreted as a string and it is not required to identify anactual webpage. For simplifying notation in the rest of the paper we represent resources with strings starting with alower case letter. The runway of the example is identifiedwith seatac_run 1 . Resources have a type that is organized ina class hierarchy. The state of the system is represented as aset of statements. Each statement represents a “fact” that itis true in the state of the system and it is expressed as a 3-tuple. For example, we can represent the fact that an aircraftlanded on runway 1 using the notation (aircraft  1  , landed, seatac_run 1  ). In this statement, the first element ( aircraft  1 )is a resource and represents the  subject  of the statement (inthis case the tail number that identifies an aircraft); the lastelement (  seatac_run 1 ) is a resource and it is called object  of the statement. The second element ( landed  ) is called  predicate and represents the type of relation between thesubject and the object (in this case that the aircraft aircraft  1  touched ground on runway  seatac_run 1 ). Unique URIstrings also identify predicates. A timestamp is associated toeach statement to identify the time at which the statement isgenerated.Policies are expressed as rules. A policy can be interpretedas  IF <condition> THEN <consequence> . The condition iscalled rule body , and the consequence is called rule head   and it is written as <body> à <head>. The body and thehead of the rule are composed of   statement patterns . Astatement pattern is a 3-tuple similar to a statement, but itcan have variables in the subject and object position.Variables are identified with an uppercase letter. For example, (A, landed, seatac_run 1  ) is   a statement pattern. Astatement pattern can match a statement if there is asubstitution of variables that make the two statement equals.In our example, the substitution  A/aircraft  1   makes thestatement pattern equals to the statement (aircraft  1  , landed, seatac_run 1  ) .The body is composed of a conjunction of statements, whilethe head is a single statement. For example, policy (17),example 2 can be encoded as (A, landed, seatac_run 2  ), (A,useNetwork, WiMAX) à  (A, violates, policy 17   ). 4.1.   E XAMPLES OF F ORMAL P OLICIES In order to be able to formalize policies we need to define avocabulary of resource classes and predicates for expressingthe state of the system. This vocabulary is called an ontology . We define the resource types airport  , runway,application, network, and maintenance_device. We alsodefine the special resource internet  to represent the publicInternet network, and the resource  ground-only to indicatethat application should be accessed only when in weight-on-wheel status.    5We define a set of predicates that describe the relation between resources. The predicate type (defined by the RDFstandard) specifies that a particular resource belongs to aclass. The predicate violation specifies that a resource isviolating a policy. The predicate  part_of  describes that aresource is part of a larger resource. For example, weidentify that an application  p 1   is managed by the airline al  1  using the statement (p 1  , part_of, al  1  ). We define predicates that are specific to the case of airports.In policy (2), the predicate landed  specifies that the aircrafthave weight-on-wheels on a runway. In policy (11), wedefine a set of predicates that provide information about thestate of the network interconnections. We define the predicate airplane_min_bw , which indicates the minimum bandwidth requirement of the plane (collected frominformation about the current applications running on theaircraft). Similarly, we define the predicate net_available_bw that define the bandwidth available in awireless network. The predicate cost identifies the cost of using a particular wireless network. The encoding of therules in Datalog is shown in the first two columns of Table 1. 4.2.   R  UNTIME V ALIDATION OF P OLICIES   The verification of policies requires aggregating informationabout the state of the system. Once information is collected,we check if the overall state triggers policy violations.In our architecture, the monitoring software running on thedevice can be configured to send messages that containupdates about the device state every time that there is a statechange. For example, when the aircraft aircraft  1 lands, adevice  s installed on the aircraft can send a message tonotify that the state of the airplane changed. This messagecontains the statement ( aircraft  1  , landed, seatac_run 1  ). Thelast column of Table 1 shows the devices providing thedifferent parts of the information about the policy. Asmultiple organizations can verify independently the policies,each device might need to send its state update informationto different entities. Section 5 describes an algorithm ondevice selection by each organization, in order to determinethe state of the infrastructure relevant to policies.Policies can also be used to define complex concepts frominformation about the system. For example, we use tworules in policy (5) to define the concept of “connected toInternet”. We say that if a device D 1 that can receivemessages from another device D 2 , then D 1 is “connected” to Policy RDF Rule Example of Sources (2) Aircraft accessing a“ground-only” airlineapplication must be inweight-on-wheelscondition. (A, type, aircraft), (P, type, application),(AL, type, airline), (R, type, runway),(A, logged_on, P), (P, part_of AL), (P, apptype, ground-only), ¬  (A, landed, R) à  (A, violation, policy 2  ) aircraft aircraft  1 : ( aircraft  1 ,landed, *)airline airline D : (*, partof,airline D ), (*, logged_on, P),(P, type(5) Maintenance devicemust be disconnectedfrom Internet whenaccessing airplanesystem (D, type, maintainance_device), (A,   type, aircraft), (N,type, network), (D 1  , type, device), (D 2  , type, device)(D, connected_to, internet), (D, connected_to, N), (N, partof, A) à  (D, violation, policy 5  )(D 1  , rec_from, D 2  ) à  (D 1  , connected_to, D 2  )(D 1  , connected_to, D 2  ), (D 2  , connected_to, internet) à  (D 1  , connected_to, internet) maintainance_device dev1:(dev1, connected_to, *)aircraft aircraft  1 : (*, partof, aircraft  1 )(11) Airplane mustautomatically choosethe cheapest availablewireless data link thatsatisfies the minimum bandwidth requirement (A, type, aircraft), (N, type, network), (M, type, network),(AIR, type, airport), (SW, type, application),(A, connected_to, N), (N, partof, AIR),(A, airplane_min_bw, MINBW), (N, cost, NC), (A, inrange, M), (M, partof, AIR), (M, net_available_bw, AVMBW), (M,cost, MC), (M != N), (MC < NC) à  (A, violation, policy 11  ) aircraft aircraft  1 : ( aircraft  1 ,connected_to, *), ( aircraft  1 ,airplane_min_bw, *),( aircraft  1 , inrange, *)airport seatac: (N, partof,seatac), (N, cost, *), (N,net_available_vw, *) Table 1: Formal representation of three airport policies. The column sources contains statement patterns thatsummarize the set of statements generated by each device.
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