Game-Theoretic Approaches to Critical Infrastructure Protection
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Game-Theoretic Approaches to Critical Infrastructure Protection Reducing the Risks and Consequences of Terrorism CREATE Conference November 18, 2004 Vicki Bier University of Wisconsin-Madison. Research Objectives. Objective:

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Game-Theoretic Approaches to Critical Infrastructure ProtectionReducing the Risks and Consequences of TerrorismCREATE ConferenceNovember 18, 2004Vicki Bier University of Wisconsin-Madison

Research objectives
Research Objectives Protection

  • Objective:

    • Study optimal allocation of resources for protection of systems against intentional attacks

  • Part of the risk modeling area:

    • With close tie to economics

    • (Game theory is a branch of economics)

  • Potentially applicable to all case studies:

    • Aviation

    • Ports

    • Electricity

Background Protection

  • Because attackers can modify their strategies in response to our defensive investment:

    • Defense will generally be more costly when the adversary can observe the system defenses

  • “Investment in defensive measures, unlike investment in safety measures, saves a lower number of lives…than the apparent direct contribution of those measures”

    • Ravid (2002)

  • Security improvements may be less cost-effective than they would initially appear

Game theory
Game Theory Protection

  • Determine the optimal defense against an optimal attack

  • Game theory is a useful model for security and critical infrastructure protection:

    • Appropriate when protecting against intelligent and adaptable adversaries

    • Recognizes that defensive strategies must account for attacker behavior

Game between attackers and defenders
Game between Attackers and Defenders Protection

  • Need to make assumptions about:

    • Attacker goals and constraints

    • Defender goals and constraints

    • System design features

  • Protective investment assumed to reduce success probability of attacks

Game between attackers and defenders1
Game between Attackers and Defenders Protection

  • Consider security of a simple series system:

    • Defending series systems against informed and determined attackers is a difficult challenge

  • If the attacker knows about the system’s defenses, the defender’s options are limited:

    • The defender is largely deprived of the ability to allocate defensive investments by their cost-effectiveness

    • Instead, defensive investments must equalize the “attractiveness” of all defended components

Importance of redundancy
Importance of Redundancy Protection

  • Parallel systems:

    • Any component can perform the function

    • Attacker must disable all to succeed

  • Series systems:

    • Attacker has a wide choice of targets

    • Defender must protect all components!

  • Physically in series (pipelines, electric lines)

  • Multiple failure modes (e.g., multiple points of entry)

Weakest link models
Weakest Link Models Protection

  • Defender must equalize the attractiveness of all defended components

  • This is generally consistent with the Brookings Institution recommendation to defend only the most valuable assets

  • However, terrorists also consider the probabilityof success in choice of targets:

    • So models should take the success probabilities of attacks against various targets into account

Attacker knowledge
Attacker Knowledge Protection

  • The assumption that attackers know our defenses may not be unrealistic:

    • Due to the openness of our society

  • Public demands knowledge of our defense:

    • Even when this weakens its effectiveness!

  • This increases difficulty of defense:

    • E.g., anthrax protection

  • Defensive measures may not be effective if they can be easily observed

System design features
System Design Features Protection

  • Redundancy reduces attacker flexibility:

    • And increases defender flexibility

  • Traditional reliability design considerations:

    • Spatial separation

    • Functional diversity

      are also important to defensive strategy

  • Examples:

    • Defenses that do not require electricity

    • Use of both land lines and satellite communications

  • Secrecy and deception can also be valuable

Extensions with hedging
Extensions with Hedging Protection

  • Real-world decision makers will want to hedge:

    • In case they guess wrong about which targets are most attractive to attackers

  • Recent work assumes that attackers target the most attractive component:

    • But defenders are uncertain about their attractiveness

  • Attackers will in general have different values for targets than defenders:

    • For example, Al-Qaeda prefers targets that are “recognizable in the Middle East” (Woo)

Extensions with Hedging Protection

  • Defending one target can deflect attacks to targets that are:

    • Less attractive to attackers (a priori)

    • But more damaging to defenders!

  • Optimal defense frequently still involves allocating zero resources to targets with a non-zero probability of successful attack, especially if:

    • Targets value widely in their values

    • Defender is highly resource-constrained

Sample application
Sample Application Protection

  • Our results shed light on appropriate allocation of resources among targets:

    • Focus on the most attractive (and most vulnerable) targets

    • Spend less money on targets that are unlikely to be attacked

  • Some states may have relatively few targets worth much investment 

Security versus safety
Security versus Safety Protection

  • In safety applications:

    • Natural hazards

    • Accident prevention

      the 80/20 rule works well:

    • Address the top 80% of the risks, at 20% of the cost

  • By contrast, in security applications:

    • It may not be worthwhile spending anything at all

    • Unless you address all serious vulnerabilities

  • Example:

    • Don’t bother searching purses and backpacks

    • If you don’t also search baby carriages!

Extensions in progress
Extensions in Progress Protection

  • More complicated system structures:

    • E.g., adapting past work on least-cost diagnosis to identify “least-cost” attack strategies

    • As a building block for optimal (or near-optimal) defenses

  • Non-convex functions for attack success probability as a function of investment:

    • If minimal levels of investment are required

    • If investment beyond a threshold deters attackers

  • Secrecy and deception:

    • When are these useful?

    • How can we quantify their benefits?

Game between defenders
Game between Defenders Protection

  • Consider effects of defensive actions on the risks faced by other defenders:

    • And therefore the strategies they adopt

  • Some defenses (e.g., car alarms) increase risk to other defenders:

    • Payoff of investing to any one individual is greater than the net payoff to society

    • Typically leads to overinvestment in security

  • Other defenses (e.g., vaccination) decrease risk to other defenders:

    • “Free riders”

    • Typically lead to underinvestment in security

Game between Defenders Protection

  • Extended an earlier “static” model by Kunreuther and Heal to account for attacks over time:

    • Example--computerized supply chain partners

  • Differences in discount rates can lead some agents not to invest in security when it is otherwise in their interests:

    • If other agents choose not to invest

  • Differences in discount rates can arise due to:

    • Industries with different rates of return

    • Risk of impending bankruptcy

    • Myopia

  • This game can have multiple equilibrium solutions:

    • Creating a need for coordinating mechanisms

Sample application1
Sample Application Protection

  • Computer security in electronic supply chains:

    • Companies may be vulnerable to weaknesses in computer security on the part of their partners

    • This can reduce their incentives to invest in their own computer security

  • Coordinating mechanisms can help to address this problem:

    • Contract terms

    • Development of international standards

    • Loans to enable partners who are not as financially stable to improve their computer security

Conclusions Protection

  • Protecting against intentional attacks must account for attacker responses:

    • Most applications of risk analysis fail to take this into account

    • Most applications of game theory to security deal with individual components in isolation

  • Combining these approaches makes it possible to invest more cost-effectively:

    • Avoids wasting resources on defenses that can easily be disabled or circumvented by attackers