Telecommunications software and multimedia laboratory

TML / Studies / T-110.402 / Homeworks

2002: Homework 2

The deadline is Tuesday 12.11. 2002 at 15:45.


Security policy models

  1. Biba model functionality in practise (9 p)

    (based on Amoroso question 12.1)

    Describe some practical situations or some systems (not necessarily a computer system) where the same principles apply as in

    1. static Biba model
    2. Subject low water mark model
    3. Object low water mark model
    Your answer should have 1 example (or scenario) per model.

  2. Chinese Wall (4 p)

    Why does Chinese Wall model have also the *-property, why is the simple security property not enough? Give an example scenario that illustrates the need of *-property.

  3. Lattices

    1. How many different security labels can be constructed with n security levels and m security categories? (2 p)
    2. Which of the following are lattices? (2 p)

      pictures of diagrams

  4. Models in practice (3 p)

    Unix System V/MLS is perhaps the most well-known MLS implementation. Linux also has MLS implementations, such as RSBAC, a security extension that implements some security policy models among other things. How does the NWD rule in the BLP-implementation of System V/MLS (and in later versions of RSBAC) differ from the NWD rule of the BLP model? (1 p) Explain why this change has been made. (2 p)

  5. Feedback (max. 2 p bonus)

    How long did it take to do this assignment? Was the assignment too easy or too difficult? How could the assignment be made better?


The answers should be written to a text file (not e.g. a MS Word document). In the beginning of your answer file you should write your name and your student number. The answer file is signed and then returned by e-mail. You can also encrypt the file with the course public key if you want to.

One way to sign the answer file is clearsigning, which does not compress the text. The can be done in following way:
gpg --clearsign -u 'my_username' ans_2.txt
where ans_1.txt is the answer file. (If you want, you can alternatively use the normal signing, i.e. the option -s instead of --clearsign)

The signed file is then sent to the address with the subject ASSIGNMENT 2
This can be done e.g. from the command line like this:
mailx -s "ASSIGNMENT 2" < ans_2.txt.asc
(Note that in the command above, the quotes are not part of the subject but they tell the shell that the subject consists of several words.)

NB: There is no automatic comfirmation for returns. Save your answer files, at least until you get results, preferably 'til the end of the course.

This page is made by assistants of the course. Newsgroup of the course: opinnot.tik.verkkoturva
Last updated 25.10.2002.