Access Control MAC

1. Access ControlMAC

2. Reading assignments Recommended: • Ravi Sandhu, Lattice-Based Access Control Models, IEEE Computer, Volume 26, Number 11 (Cover Article), November 1993 http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.54.8395 CSCE 522 - Farkas

3. Mandatory Access Control • Objects: security classification e.g., grades=(confidential, {student-info}) • Subjects: security clearances e.g., Joe=(confidential, {student-info}) • Access rules: defined by comparing the security classification of the requested objects with the security clearance of the subject e.g., subject can read object only if label(subject) dominates label(object) CSCE 522 - Farkas

4. Mandatory Access Control • If access control rules are satisfied, access is permitted e.g., Joe wants to read grades. label(Joe)=(confidential,{student-info}) label(grades)=(confidential,{student-info}) Joe is permitted to read grades • Granularity of access rights! CSCE 522 - Farkas

5. Mandatory Access Control Security Classes (labels): (A,C) A – total order authority level C – set of categories e.g., A = confidential > public , C = {student-info, dept-info} (confidential,{student-info,dept-info}) (confidential,{student-info}) (confidential,{dept-info}) (confidential,{ }) (public,{student-info,dept-info}) (public,{student-info}) (public,{,dept-info}) (public,{ }) CSCE 522 - Farkas

6. Mandatory Access Control • Dominance (): label l=(A,C) dominates l’=(A’,C’) iff A  A’ and C  C’ e.g., (confidential,{student-info})  (public,{student-info}) BUT (confidential, {student-info})  (public,{student-info, department-info}) CSCE 522 - Farkas

7. Bell- LaPadula (BLP) Model • Confidentiality protection • Lattice-based access control • Subjects • Objects • Security labels • Supports decentralized administration CSCE 522 - Farkas

8. BLP Reference Monitor • All accesses are controlled by the reference monitor • Cannot be bypassed • Access is allowed iff the resulting system state satisfies all security properties • Trusted subjects: subjects trusted not to compromise security CSCE 522 - Farkas

9. BLP Axioms 1. Simple-security property: a subject s is allowed to read an object oonly if the security label of s dominates the security label of o • No read up • Applies to all subjects CSCE 522 - Farkas

10. BLP Axioms 2. *-property: a subject s is allowed to write an object oonly if the security label of o dominates the security label of s • No write down • Applies to un-trusted subjects only CSCE 522 - Farkas

11. Blind Writes • Improper modification of data • Most implementations disallow blind writes CSCE 522 - Farkas

12. Tranquility • Read and write accesses mediated based on the security labels of objects and subjects • Read and write accesses are not atomic, i.e., sequences of operations that may or may not be interrupted • Example: secret subject requests a read to a secret object. While the request is being processed, the subjects lowers its level to unclassified => unclassified subject gained read access to secret object CSCE 522 - Farkas

13. Tranquility • Tranquility: changing security labels • Strong tranquility: security labels of subjects and objects never change during an operation • Advantage: system state always satisfies security requirements • Disadvantage: not flexible CSCE 522 - Farkas

14. Tranquility • Weak tranquility: security labels of subjects and objects never change such a way as to violate the security policy • High watermark on subject: during read a subject may upgrade its security clearance • High watermark on objects: during write an object’s security classification may be upgraded. CSCE 522 - Farkas

15. Discretionary Security Property • Every current access must be in the access matrix CSCE 522 - Farkas

16. Trojan Horse and BLP Brown: read, write Reference Monitor Employee Word Processor Secret Use shared program Read Employee Brown Black, Brown: read, write Secret Black’s Employee TH Copy Employee To Black’s Employee Public Insert Trojan Horse Into shared program Black Secret  Public Public CSCE 522 - Farkas

17. Biba Model – Integrity Protection • Integrity protection • Lattice-based access control • Subjects • Objects • Integrity labels • Access Control List CSCE 522 - Farkas

18. Integrity Labels • Hierarchical integrity levels: e.g., Crucial > Very important > Important • Non-hierarchical categories: e.g., {medical, personal, administrative} CSCE 522 - Farkas

19. Strict Integrity Policy • Integrity *-property: a subject s can modify an object o only if the integrity level of the subject dominates the integrity level of the object (no write up) • Simple integrity property: a subject s can observe an object o only if the integrity label of s is dominated by the integrity label of o (no read down) • Invocation property: a subject s1 can invoke a subject s2 only if the integrity label of s1 dominates the integrity label of s2 CSCE 522 - Farkas

20. Next Class: Database Security CSCE 522 - Farkas