Lecture 13 Outline
Reading: text, §5, 6.1, 6.2, 6.4, 10
Due: Homework 3, on May 12
- Greetings and felicitations!
- Discussion question
- Example: Trusted Solaris
- Declassification problem
- Strong tranquility
- Weak tranquility
- Requirements of integrity models
- Biba Model (strict integrity policy)
- Clark-Wilson Model
- Theme: military model does not provide enough controls for commercial fraud, etc. because it does not cover the right aspects of integrity
- Constrained Data Items (CDI) to which the model applies
- Unconstrained Data Items (UDIs) to which no integrity checks are applied
- Integrity Verification Procedures (IVP) that verify conformance to the integrity spec when IVP is run
- Transaction Procedures (TP) takes system from one well-formed state to another
- Clark-Wilson Certification and Enforcement Rules
- [C1] All IVPs must ensure that all CDIs are in a valid state when the IVP is run.
- [C2] All TPs must be certified to be valid, and each TP is associated with a set of CDIs it is authorized to manipulate.
- [E1] The system must maintain these lists and must ensure only those TPs manipulate those CDIs.
- [E2] The system must maintain a list of User IDs, TP, and CDIs that that TP can manipulate on behalf of that user, and must ensure only those executions are performed.
- [C3] The list of relations in E2 must be certified to meet the separation of duty requirement.
- [E3] The system must authenticate the identity of each user attempting to execute a TP.
- [C4] All TPs must be certified to write to an append-only CDI (the log) all information necessary to reconstruct the operation.
- [C5] Any TP taking a UDI as an input must be certified to perform only valid transformations, else no transformations, for any possible value of the UDI. The transformation should take the input from a UDI to a CDI, or the UDI is rejected (typically, for edits as the keyboard is a UDI).
- [E4] Only the agent permitted to certify entities may change the list of such entities associated with a TP. An agent that can certify an entity may not have any execute rights with respect to that entity.
- Codes vs. ciphers
- Attacks: ciphertext only, known plaintext, chosen plaintext
- Types: substitution, transposition
- Classical Cryptography
- Monoalphabetic (simple substitution): f(a) = a + k mod n
- Example: Caesar with k = 3, RENAISSANCE → UHQDLVVDQFH
Discussion question. An eighth grade school student in Florida shoulder-surfed a teacher he didn’t like typing in a password. He used that password to log into the teacher’s account and changed the wallpaper. The password, like all passwords on the school network, was the last name of the teacher (user), and teachers had administrative privileges on the network.
The student was first suspended for 10 days. But on April 2, 2015, the Pasco County sheriff filed felony charges against the student. The sheriff stated that he filed the charges because the teacher’s computer had “encrypted 2014 FCAT [Florida Comprehensive Assessment Test] questions”, although he admitted the student “did not view or tamper with those files.” He added “Even though some might say this is just a teenage prank, who knows what this teenager might have done.”
Do you think the student should have been suspended? Should he have been charged with a felony?