Pushing the Security Boundaries of Ubiquitous Computing

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					         Pushing the Security Boundaries of
         Ubiquitous Computing

                   ACSF 2006
                          ——————


                       13th July 2006
                          ——————


David Llewellyn-Jones, Madjid Merabti, Qi Shi, Bob Askwith
                          ——————


       School of Computing and Mathematical Statistics
              Liverpool John Moores University
                   James Parsons Building
            Byrom Street, Liverpool, L3 3AF, UK

 {D.Llewellyn-Jones, M.Merabti, Q.Shi, R.Askwith}@ljmu.ac.uk
              http://www.cms.livjm.ac.uk/PUCsec/
                   Overview


• Perimeter Security
   – Ubiquitous Computing
   – Dynamic Boundaries
• Component Composition Analysis
   – Implementation Framework
   – Dynamic Boundary Analysis
• Encrypting External Links
   – Resolving Failures
• Complexity and Timing
• Conclusions and further work
                   Perimeter Security


• Computer security currently relies heavily on perimeter
  defences
   – Firewalls
       – Block certain types of incoming and outgoing traffic
   – Intrusion Detection Systems
       – Analyse data entering or leaving a network
       – Detects Denial of Service attacks
   – 97% of organisations responding to the 2005 CSI Computer Crime and
     Security Survey used a firewall


• Policies enforced within network boundaries
                   Ubiquitous Computing Perimeters


• In Ubiquitous Computing environments, the perimeter
  becomes blurred
   – Wireless ad hoc networks
   – Dynamic devices and services moving in and out of networks


• No centralised control, possibly no ownership of devices

• How can the perimeter model of policy enforcement be
  adapted to cope?
                    Alternatives to Perimeter Security


• Security on every device
   – May not be appropriate on low power
     devices
   – Often not necessary
• Distributed security
   – A good solution
   – Can be difficult to design and deploy
     such solutions
• Dynamic boundaries
   – Need a process for establishing where the boundaries lie
   – Must dynamically update security
               Dynamic Boundaries


• As devices join and leave, we need a way to dynamically re-
  establish the boundary through remote analysis
                    Component Composition

• In systems without clear boundaries, component
  composition may be a way to ensure security
   – Analyse interaction between devices
   – Ensure that interactions do not affect security
• For example
   – Buffer overrun checking based on interaction between pairs of nodes
   – Access control by following data flow through components
   – Composable Assurance
      – Certain properties can be assured in a complete system if they can be
         shown to hold at the boundaries
      – Shi and Zhang ―An Effective Model for Composition of Secure Systems,‖
         Journal of Systems and Software, 43(3) 1998
                    Application of Component
                    Composition
• Composition properties combine
   – Properties of individual components
   – The interaction between components (the component topology)
• We can therefore use component composition results in two
  ways
   – Boundary analysis is a composition property
   – Dynamic boundary analysis can allow further properties to be applied to
     systems
• Boundary analysis as a simple composition property
   – Nodes identified with the property of being internal
   – Analyse the topology to establish the boundary based
      – internal – internal links
      – internal – external links
• Having analysed the boundary, can consider other
  security properties
                   Analysis Implementation


• Use the MATTS composition tool
   – Allows composition of systems based on
      – Simulated components
      – Interacting agents
      – Networked Appliance service architecture
• Analyse composition structure using a script
• Presently uses a combination of
   – Certification
   – Formal analysis
   – Topology analysis
                   Framework


• Undertaken in two phases
   – Instrumentation
       – Establish the dependencies between
         components
       – Relates to the movement of data
   – Composition analysis
       – Establish properties of the composed
         system based on the dependencies
       – May require properties of individual
         components to be established to
         complete the composition analysis
                    Composition Analysis


• Analyse a system based on its dependencies
   – Undertaken whenever the dependencies change
   – Result determines whether the security property is satisfied or not
   – Combined with specific security property, establishes whether a particular
     composed system is safe


• How is this undertaken? Analysis is directed by a script
   – Simple XML language script
   – Each script designed for a particular property
                   Composition Script

• What does the script actually do?
   – Script describes a set of satisfying topologies
   – Applied to the composition structure to determine whether the topology
     satisfies it or not
• For example
   – Binary trees
   – Structures without cycles/loops
   – Can depend on the properties of individual components
• Script engine maintains two positions
   – Current position in script
   – Current position in dependency digraph
• We require the dependency digraph to do this
Boundary Analysis Script


                        Set up script




                     Negotiate structure



                      External link and
                       not encrypted?
                    Encrypting External Links

• The script traverses the component structure
• For links from internal to internal nodes
   – No checks are performed
   – The traversal continues along the next link from the internal node
• For links from internal to external nodes
   – The properties of the link are tested
   – If the link is not encrypted, the script fails
   – The traversal continues along the next link from the internal node
• Links from internal nodes are followed, but not those from
  external nodes
• All links that are not internal must be encrypted
• The analysis must be performed each time the
  topology changes
                     Resolving Failures

• The script is used to identify failures of the security policy
• It can also be used to resolve the failures
   – At failure, the problematic link can be identified




   – Generate new encryption service via software factory
   – Place within network between the offending components
                Complexity

• Node traversal


• Encryption checking




• Combined

• The algorithm is dominated by the depth first
  traversal of the nodes
Simulation Timings
                  Conclusions and Future Work


• Perimeter model is currently very successful
• Future changes may make it less applicable
• Dynamic boundary analysis may provide an interim
  measure
   – Achieved through component composition analysis
   – Used to enforce component composition results


• Aim to apply the technique to a Networked Appliance
  scenario
• Create specific security enforcement cases