**Due Date**: April 19, 2001

**Points**: 100

- (
*20 points*; text, exercise 1.3) The aphorism "security through obscurity" says that hiding information provides some level of security. Please give an example of a situation in which hiding information does not add appreciably to the security of a system. Give an example when it does. - (
*20 points*; text, exercise 2.5) Let*c*be a copy flag and let a computer system have the set of rights {*r*,*w*,*x*,*a*,*l*,*m*,*o*}.- Using the syntax in class (and in section 2.3 of the text),
write a command
*copy_all_rights*(*p*,*q*,*s*) that copies all rights that*p*has over*s*to*q*. - Modify your command so only those rights with an associated copy flag are copied. The new copy should not have the copy flag.

- Using the syntax in class (and in section 2.3 of the text),
write a command
- (
*40 points*; text, exercise 3.1) Prove or give a counterexample:

The predicate*can*share*(*a*,*x*,*y*,*G*_{0}) is true if and only if there is an edge from*x*to*y*in*G*_{0}labelled*a*, or if the following hold simultaneously:- there is a vertex
*s*in*G*_{0}with an*s*-to-*y*edge labelled*a*; - there is a subject vertex
**x'**such that**x'**=**x**or**x'**initially spans to**x**; - there is a subject vertex
**s'**such that**s'**=**s**or**s'**terminally spans to**s**; and - there is a sequence of subjects
**x'**=**x**_{1}, ...,**x**_{n}=**s'**with**x**_{i}and**x**_{i+1}(1 <= i < n) being connected by an edge labelled*t*, an edge labelled*g*, or a bridge.

- there is a vertex
- (
*20 points*; text, exercise 4.5) Classify each of the following as examples of mandatory, discretionary, or originator controlled policies, or a combination. Please justify your answers.- The file access control mechanisms of the UNIX operating system.
- A system in which no memorandum can be distributed without the author's consent.
- A facility in which only generals can enter a particular room.
- A university's registrar office, in which faculty can see grades of a particular student provided that student has given written permission.

Matt Bishop Office: 3059 Engineering Unit II Phone: +1 (530) 752-8060 Fax: +1 (530) 752-4767 Email: bishop@cs.ucdavis.edu | Copyright Matt Bishop, 2001. All federal and state copyrights reserved for all original material presented in this course through any medium, including lecture or print. |