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. What is a certificate? What is it used for?

6. 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);
   }
   

7. Show how ACLs and C-Lists are derived from an access control matrix.

8. Discuss the revocation problem with respect to access control lists and capabilities. How might one efficiently implement a command to revoke access to an object by one particular user?

9. 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?