Lec 1: Intro Flashcards
What is computer security?
It is about how the embodiment of functionality behaves in the presence of an adversary
What makes computer security different from most other fields of CS?
Most of CS is about providing functionality, computer security is not
What is the binary model?
it’s a security philosophy that is:
- traditional crypto and trustworthy systems
- assume adversary limitations X and define security policy Y
- if Y cannot be violated without needing X then system is secure, else insecure
What is the risk management model?
it’s a security philosophy that is:
- most commercial software development (and much real-world security…e.g., terrorism)
- try to minimize biggest risks and threats
- improve security where most cost effective (expected value)
What model does the perfect substitution cipher follow?
the binary model
What is the perfect substitution cipher?
- invented by Vernam & Mauborgne in 1919
- choose a string of random bits the same length as the plaintext, XOR them to obtain the ciphertext
- perfect secrecy (proved by claude shannon)
What is perfect secrecy?
- probability that a given message is encoded in the ciphertext is unaltered by knowledge of the ciphertext
Generally explain the proof of perfect secrecy in the perfect substitution cipher?
Give me any plaintext message and any ciphertext and I can construct a key that will produce the ciphertext from the plain text. Zero information in ciphertext
What model does the concrete barricade security solution follow? What is the problem that it solves?
- risk management model
- prevents incursion by car bombers by preventing cars from getting too close to the building
What are some of the problems with the binary model of security?
- Many assumptions are brittle in real systems
- real artifacts fragile, imperfect, have bugs/limitations
- implicit dependencies with exposed layers
– ex: reading secret bits off current draw on a chip
- Hard to know what security policy should be
- hugely expensive
What are some problems with risk management model of security?
- creates arms races
- forced co-evolution
- (adversary invents new attack -> defender creates new defense -> repeat) - security is a spectrum, but how to evaluate risk or reward?
- best you can hope for is stalemate
- and we’re losing stalemate in a number of situations (e.g. SPAM, Malware)
What are the key meta issues in security?
- policy
- risks
- threats
- value
- protection
- identity & reputation
What questions do you have to ask when coming up with policy? What makes it difficult?
- what is a bad thing?
- remarkably tricky to define for known threats
- the software on your computer likely has 100s of security options…how should you set them?
- what might be a good security policy for who gets to access faculty salary data? - Even harder for unknown threats
- SPAM - Can be non-intuitive
- should a highly privileged user have more rights on a system or less?
What questions do you have to ask when dealing with risks& threats?
Risk
- what bad things are possible?
- How bad are they and how likely are they?
Threats
- who is targeting the risk?
- what are their capabilities?
- what are their motivations?
How formalized are risks and threats?
tend to be well formalized in some communities (e.g. finance sector) and less in others (e.g. energy sector)
Draw/describe the Threat Landscape
