程序代写 CSE 127: Introduction to Computer Security

CSE 127: Introduction to Computer Security
Spring 2022 Lecture 1 (Continued)

Continued from Threat Modeling

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Thinking like a Defender
• Security policy
• Whatarewetryingtoprotect?
• Whatpropertiesarewetryingtoenforce?
• Threat model
• Who are the attackers? Capabilities? Motivation? • Whatkindofattackarewetryingtoprevent?
• Risk assessment
• Whataretheweaknessesofthesystem?
• Whatwillsuccessfulattackscostus? • Howlikely?
• Countermeasures
• Costs vs. benefits?
• Technical vs. nontechnical?

Security Policies
What assets are we trying to protect?
• Password (hashes): Secret code for authentication.
• Emails: System for sending and receiving messages electronically.
• Browsing history: Pages visited, useful for web marketing and forensics.

Security Policies
What properties are we trying to enforce? (CIA triad)
• Confidentiality: Protect sensitive and private information from unauthorized use.
• Integrity: Protect data from deletion or modification from any unauthorized party.
• Availability: Refers to the actual availability of information.
• Privacy: Protect sensitive information, such as personally identifiable information, etc.
• Authenticity: Proven fact that something is legitimate or real.

Scenario 1
Rob opens his fitness tracking app to start logging a workout. The app crashes, and Rob was unable to log his workout.
a. Confidentiality b. Authenticity
c. Availability
d. None of the above
Go to www.menti.com and use the code: 35 28 617

Scenario 2
Kim selected an Easter egg on an XYZ e-commerce platform for $10. At checkout, Kim was asked to pay $1000.
a. Confidentiality b. Integrity
c. Availability
d. None of the above
Go to www.menti.com and use the code: 5219 7835

Scenario 3
Bob works for a finance company called ABC123. Six months into the position, Bob stole and sold 250,000 customer credit card information on the darkweb.
a. Confidentiality b. Integrity
c. Availability
d. None of the above
Go to www.menti.com and use the code: 8130 7884

Threat Models
Identifies the types of threat agents that cause harm to computer systems.
• Who are our adversaries?
• Motives?
• Capabilities?
• What kinds of attacks do we need to prevent? (Think like the attacker!)
• Limits: What kinds of attacks should we ignore?

Example of Threat Modeling
“This World of Ours”

Example of Threat Modeling

Assessing Risk
Remember: Controlled paranoia
• What would security breaches cost us?
• Directcosts:Money,property,safety,…
• Indirectcosts:Reputation,futurebusiness,wellbeing,
• How likely are these costs?
• Probabilityofattacks? • Probabilityofsuccess?

Countermeasures
• Technical countermeasures
* Firewalls, Anti-virus programs, IDS programs, etc.
• Nontechnical countermeasures
* Law, policy (government, institutional), procedures, training, auditing, incentives, etc.

How do we protect classified satellites?

Secure Design
• Common mistake:
Convince yourself that the system is secure
• Better approach:
Identify weaknesses of design, focus on correcting them Formally prove that design is secure (soon)
• Secure design is a process
Must be practiced continuously Retrofitting security is super hard

Where to focus defenses
• Trusted components
Parts that must function correctly for the system to be secure.
• Attack surface
Parts of the system exposed to the attacker
Security Principles
• Simplicity, open design, and maintainability • Privilege separation and least privilege
• Defense-in-depth and diversity
• Complete mediation and fail-safe

Preventing cheating on an online exam?

Preventing you from stealing my password?

Security Costs
• No security mechanism is free
• Directcosts:
Design, implementation, enforcement, false positives
• Indirectcosts:
Lost productivity, added complexity
• Challenge is to rationally weigh costs vs. risk
• Humanpsychologymakesreasoningabouthigh cost/low probability events hard

Group Discussion

Should you lock your door?
• Adversaries?
• Risk assessment?
• Countermeasures? • Costs/benefits?

Should you use automatic software updates?
• Adversaries?
• Risk assessment?
• Countermeasures? • Costs/benefits?

Next lecture: Buffer overflows!

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