Lecture 20 Trusted Operating System

The lecture began today with a presentation by Spencer Dawson on Rainbow Tables and there use to crack passwords. A rainbow table is a lookup table that offers a time-memory tradeoff used in recovering the plain text password from a password hash. The table contains a hash for all possible inputs up to a character limit. These tables have both advantages and limitations. The advantages include the fact that they are built once, and used many times, they make looking for a password faster as the lookup becomes a table search problem, and they are perfect for cracking weak hashes. The limitations on these tables are that they are generated always in the worst case time complexity. They are very large, a table for 8 characters is 134.6 GB, and they become infeasible when passwords are salted.

After the presentation, we continued with a lecture on Trusted Operating Systems. The operating system is a complex system, that is very difficult design and this complexity added with the securities issues makes it a very difficult design problem. By following the path of listing requirements, designing, and then testing the creation of the system can be done. There are several security design principles. These principles include privileges, permissions, separation of privileges, and ease of use. The feature normally included in an ordinary OS include authentication of users, protection of memory, File I/O and location and access control to general objects. Security features in ordinary OS include enforcement of sharing, fair service, and protection of OS protection data. There are more features that are included in an trusted OS including, identifcation and authentication, mandatory access control, object reuse protection, trusted path, accountability and audit, and intrusion detection.

The kernel is part of the OS that performs lowest level functions and the security kernel is responsible for security mechanisms for the entire OS. The kernel is responsible for 6 functions coverage, separation, unity, modifiability, compactness, and verifiability.