Sample Final

These are sample questions that are very similar to the ones I will ask on the final.

1. In computer security, a Trojan horse is:
   1. A program that has components distributed over many systems, and is used to launch denial of service attacks
   2. A program that absorbs all available resources of a particular type
   3. A program with an overt, known purpose and a covert, unknown (and probably undesireable) purpose
   4. A program that blocks any incoming spam emails
2. How does the Clark-Wilson model require authentication of users to be done?
   1. A trusted user must vouch for the new user
   2. Two-factor authentication must be used
   3. If passwords are used, they must be at least 12 characters long, and use a mixture of letters, digits, and other characters
   4. None of the above
3. Which of the following does the Needham-Schroeder protocol require?
   1. A trusted third party
   2. A public key cryptosystem
   3. A certificate authority to identify the users
   4. A connection to the Internet
4. Consider a system that used the Bell-LaPadula model to enforce confidentiality and the Biba model to enforce integrity.
   1. If the security classes were the same as integrity classes, what objects could a given process (with some security class that also served as its integrity class) access?
   2. Why is this scheme not used in practice?
5. Define each of the following terms in one short sentence:
   1. public key cryptosystem
   2. challenge-response
   3. computer worm
   4. end-to-end encryption
6. What is a certificate? What is it used for?
7. The following routine reads a file name from the standard input and returns its protection mode. It treats the argument as a file name, and returns the protection mode of the file as a short integer. Identify three non-robust features of this routine, and state how to fix them.

   /* return protection mode of the named file */
   short int protmode(void)
   {
       struct stat stbuf;
       char inbuf[100];
   

       gets(inbuf);
       stat(inbuf, &stbuf);
       return(stbuf.st_mode&0777);
   }

8. Show how ACLs and C-Lists are derived from an access control matrix.
9. Consider the problem of managing certificates. One expert said that a hierarchical scheme, such as that employed by PEM, is more likely to be used for business than the Web of Trust employed by PGP. What specific features of the hierarchical system as implemented for PEM (and for other Internet applications) led him to make this assertion? Why might these features lead him to make this statement?
10. Why do some organizations use a DMZ in their network configuration, rather than simply filtering traffic and allowing connections intended for the web and email servers to pass through the firewall?

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu

ECS 153, Computer Security Version of June 2, 2018 at 12:40AM

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