CIT 380: Securing Computer Systems

Security SolutionsPart 2

CIT 380: Securing Computer Systems Slide #2

Assumptions

• Security rests on assumptions specific to type of security required and environment.

Assumptions

• Example: – TCP/IP designed for pre-commercial Internet.• Assumed only legitimate administrators had root

access.• Trusted IP addresses, since only root can set IP address.• What happens to network when Windows 95 systems

added to network, where desktop user has all privileges?

CIT 380: Securing Computer Systems Slide #3

CIT 380: Securing Computer Systems Slide #4

Assurance

How much can you trust a system?Example:– Purchasing aspirin from a drugstore.– Bases for trust:• Certification of drug by FDA.• Reputation of manufacturer.• Safety seal on bottle.

CIT 380: Securing Computer Systems Slide #5

How much do you trust? Ken Thompson’s compiler hack from

“Reflections on Trusting Trust.”– Modified C compiler does two things:• If compiling a compiler, inserts the self-replicating

code into the executable of the new compiler.• If compiling login, inserts code to allow a backdoor

password.

How much do you trust?

– After recompiling and installing old C compiler:• Source code for Trojan horse does not appear

anywhere in login or C compiler.• Only method of finding Trojan is analyzing binary.

CIT 380: Securing Computer Systems Slide #6

CIT 380: Securing Computer Systems Slide #7

Key Points• Components of security– Confidentiality– Integrity– Availability

• States of information– Storage, Processing, Transmission

• Evaluating risk and security solutions.– Security is a matter of trade-offs.

• Security is a human problem.

Discussion: Gas Drive Away Without Paying

• What measures can be imposed?• What are the costs for the merchant and the

customer?• Do the benefits outweigh the costs?

CIT 380: Securing Computer Systems Slide #9

References1. Ross Anderson, Security Engineering, Wiley,

2001.2. Matt Bishop, Introduction to Computer Security,

Addison-Wesley, 2005.3. Peter Neumann, (moderator), Risks Digest,

http://catless.ncl.ac.uk/Risks/4. Bruce Schneier, Beyond Fear, Copernicus Books,

2003.5. Ken Thompson, “Reflections on Trusting Trust”,

Communication of the ACM, Vol. 27, No. 8, August 1984, pp. 761-763 (http://www.acm.org/classics/sep95/)