Part One: Short answer questions: 4 Marks
Determine the entropy associated with the following method of generating a password. 1 Mark
Choose, and place in this order, one lower case letter, following by one upper case letter, followed by two digits, followed by @, followed by two letters, each upper or lower case, and then followed by three symbols drawn from the set {$,9,5,v,w,J}. Finally, apply the hash function Tiger to give an output string in hex which will be used as a password.
Assume random choices are made with equal likelihood of each symbol from the space being chosen from. So for a random digit there are 10 possibilities, each chosen with probability 1/10.
Generate a BLP lattice–structured system where the objects and subjects are appropriately levelledto give access consistent with the access control matrix below. You need to describe the process by which you obtain your lattice. R and W correspond, respectively, to read and append. You are to use only the mandatory BLP rules, and a default allow in place of the discretionary rule. Be sure to add a level as necssary to ensure this is a lattice. 2 Mark
O1 O2 O3 O4 O5 O6
S1 R R R R R RW
S2 R W W W
S3 R RW RW W W
S4 R R W
S5 R
S6 R R R R
For the following collection of statements, describe the sets of actions, objects, and subjects; anddraw an access control matrix to represent the scenario. 1 Mark Alice can climb trees and eat apples.
Bob can climb fences, eat apples, and wave flags.
Trees can hurt apples.
Carol can jump waves and wave flags.
Part Two: Authentication and access control system 10 Marks
You are to implement a simple “file system” with login authentication and access control. Specifically:
Construct a hash/salt/shadow based user/password creation system.
Construct a hash/salt/shadow based user authentication system.
Construct an associated file system, into which a user can log. Files can be created, read from, written to, but only in accordance with a four–level access control model.
The levels of the four–level access control model are 0, 1, 2 and 3. 0 is dominated by 1, 2 and 3; and 1 and 2 are dominated by 3; and 1 is dominated by 2.
Remark: You do not need to have an actual file system, simply an internal collection of records at the levels specified.
You can implement the program in C++, C or Java. You will use MD5 in this task.
The initialisation details
Your program will, initially, need blank files salt.txt and shadow.txt.
Running your FileSystem with the instruction
FileSystem -i
runs the hash/salt/shadow based user/password creation system. This program should prompt for a username, something like…
Username: Bob
Check if the username exists already. If it does, terminate the program with an appropriate notification to the user. If it doesn’t, request a password with something like …
Password: ……..
Confirm Password: ……..
You should add some appropriate checks on the password and give a warning if the user fails to meet a requirement. The warning should explain what the requirements are. Assuming the passwords are acceptable and the same, we make a final request of the user, something like …
User clearance (0 or 1 or 2 or 3): 1
Once we have this information we can modify the salt.txt and shadow.txt files to include this user. To salt.txt we add a line, with a generic example and a specific one for user Bob given here:
Username:Salt Bob:38475722
where Salt is a randomly chosen string of 8 digits.
We also add a line to shadow.txt, with a generic example and a specific one for user Bob given here:
Username:PassSaltHash:SecurityClearance
Bob:dd2da44f4437d529a80809932cb3da83:1
PassSaltHash is generated as the MD5 hash of the concatentation of the user’s password with the salt, For example if the Password is “alphabet” and the Salt is “12345678”, we would pass “alphabet12345678” to the MD5 function.
Logging in
Running FileSystem with no arguments will allow a user to try and log into the file system.
Remark: The file Files.store needs to be loaded, see later as to what this contains.
Username: Bob
Password: ……..
The system checks if the Username is listed in the file salt.txt. If the Username is in the file then their salt value is retrieved and the PassSaltHash is generated. A message should be displayed to indicate that the salt has been retrieved.
Bob found in salt.txt salt retrieved: Salt hashing … hash value: PassSaltHash
The system should now compare the PassSaltHash value with that in the file shadow.txt. If the information in shadow.txt doesn’t match the generated information, FileSystem should stop with appropriate error messages.
If the shadow.txt information matches, the clearance of the user is reported, and authentication is reported to be complete.
Authentication for user Bob complete. The clearance for Bob is 1.
Once logged in …
A list of allowed actions is now displayed
Options: (C)reate, (A)ppend, (R)ead, (W)rite, (L)ist, (S)ave or (E)xit. (1)
The C option will result in a request for filename from the client.
Filename: alpha
The classification level of a “file” is the same as its owner’s clearance level.
The program should maintain a list of “files” as internal entries. If the passed file doesn’t exist, it’s name, owner and classification should be added to the list. If the passed file does exist an appropriate message should be displayed and the system should re–display the menu marked (1). The A, R and W choices each results in a request for a filename.
Filename: alpha
Again a check is made as to whether the file exists. If the file doesn’t exist an appropriate error message should be provided and the menu (1) should be re–displayed. If the file does exist, a message informing success or failure will be displayed. Success or failure is determined by the relative clearance of the user and the classification of the file they are trying to access, in accordance with the Bell–LaPadula model. Subsequently the menu (1) should be re–displayed.
The L option lists all files in the FileSystem records. The S option saves all the data to a file Files.store. This file should be human readable. This file should always be loaded if it is available when FileSystem starts without the -i argument.
The E option should exit the FileSystem, after checking with the user:
Shut down the FileSystem? (Y)es or (N)o
NOTE: When your program starts, before bringing up a prompt, it should report a test output of the MD5. You should call your MD5 with the string “This is a test”.
MD5 (“This is a test”) = ce114e4501d2f4e2dcea3e17b546f339 Don’t hard code this output.
