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Detecting Cognitive Causes of Confidentiality Leaks

Detecting Cognitive Causes of Confidentiality Leaks. Rimvydas Rukšėnas , Paul Curzon (Queen Mary, University of London) Ann Blandford (University College London). The topic.

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Detecting Cognitive Causes of Confidentiality Leaks

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  1. Detecting Cognitive Causes of Confidentiality Leaks Rimvydas Rukšėnas, Paul Curzon (Queen Mary, University of London) Ann Blandford (University College London) FMIS 2006, Macau

  2. The topic • Ensuring (by formal modelling and verification) secure information flow from the user to a secure device / application. FMIS 2006, Macau

  3. The context • Security of software systems (technical aspects): • the implementation of a system does not leak confidential information. • User-centred security (social dimensions): • work practices; • the relationships between system users; • security threats exploiting social engineering techniques. FMIS 2006, Macau

  4. Our focus • Potential leaks of information caused by the combination of human cognition and interface designs. FMIS 2006, Macau

  5. Outline • Formal user model. • An example. • Conclusion. FMIS 2006, Macau

  6. Formal user modelling • Even behaving rationally, humans systematically make errors when performing tasks with interactive systems. • The erroneous actions are unintentional. They emerge from a combination of specific design decisions and human cognition. • A formal model of cognitively plausible behaviour is helpful in detecting such design flaws. FMIS 2006, Macau

  7. Abstract cognitive principles • Non-determinism: any cognitively plausible action might be taken. • Distinction between mental and physical actions. • User goals: preconceived knowledge of the task and task dependent sub-goals. • Reactive behaviour: people respond to interface prompts, if these seem relevant to their task. • Goal based task completion: users tend to finish interactions once their goal has been achieved. • No-option based termination. FMIS 2006, Macau

  8. UserModel {goals,acts,…} = … TRANSITION ([]i: Goal_Commit: … ) [] ([]i: React_Commit: … ) [] ([]i: Goal_Transition: … ) [] ([]i: React_Transition: … ) [] Exit: … [] Abort: … [] Idle: … Goal_Transition: gcommit[i] = committed  Transition(i,goals); gcommit’[i] = done; gcommitted’ = FALSE Generic user model in SAL FMIS 2006, Macau

  9. An example: authentication interface FMIS 2006, Macau

  10. Authentication procedure as a FSM FMIS 2006, Macau

  11. The structure of specifications FMIS 2006, Macau

  12. Enter user name. Enter password. seen[InputName]  value' [InputName] = in.name User goals (knowledge) FMIS 2006, Macau

  13. Enter user name. Enter password. Press Enterbutton. Acknowledge a message. seen[InputName] mem.failed  mem.entered[InputName]  value'[InputName] = in.name Reactive behaviour FMIS 2006, Macau

  14. User perception & interpretation • By label: (i,j): label[i] = NameLabel  label[j] = PassLabel  InputName = i InputPass = j • By habit: (i,j): precedes(i,j) InputName = i InputPass = j • Random: (label[i] = label[j] ((i,j): precedes(i,j)))  InputName  InputPass FMIS 2006, Macau

  15. Correctness properties • Usability:System F(LoginMsg) • Security: System [] Tester G(SecurityBreach) • Testermodule: [](j:Inbox): level[j] = Low  value[j] = env.password  SecurityBreach' = TRUE FMIS 2006, Macau

  16. Confidentiality leakage • precedes(InputName,InputPass) FMIS 2006, Macau

  17. Secure design • precedes(InputName,InputPass) FMIS 2006, Macau

  18. Conclusions • We investigated the formal modelling of cognitive aspects of confidentiality leaks. • We extended our approach, based on usability verification, to address some aspects of information-flow security. • We presented a simple example where the layout of input fields can result in security breaches: www.dcs.qmul.ac.uk/~rimvydas/usermodel/fmis06.zip FMIS 2006, Macau

  19. Future work • Other (more complex) security properties. • Generic user interpretation model. • Scaling-up. FMIS 2006, Macau

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