Sample Final Exam
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
/* return protection mode of the named file */
short int protmode(void)
struct stat stbuf;
Define each of the following terms in one short sentence:
- public key cryptosystem
- end-to-end encryption
- principle of fail-safe defaults
Show how ACLs and C-Lists are derived from an access control
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?
Consider the Bell-LaPadula multilevel security model. If a subject with
security label (L, C) can read an object with security
label (L', C'), then (L, C) is said to
dominate (L', C'). Prove that this dominates
relation is reflexive, antisymmetric, and transitive.
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?
Why is a precise statement of security requirements critical to the
determination of whether a given system is secure?
System vendors often add security features to strengthen the security of
their systems. These additions are not designed into the system, but
rather are added after the system has been shipped. Discuss whether
adding security features to a large, complex operating system not
designed with security in mind (such as the UNIX operating system or
Windows 95) violates any of Saltzer's and Schroeder's design principles.
(Go through all 8 design principles.)
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Department of Computer Science
University of California at Davis
Davis, CA 95616-8562
Page last modified on 12/12/99