# George Mason University

## Presentation on theme: "George Mason University"— Presentation transcript:

George Mason University
SESSION LATTICE-BASED ACCESS CONTROL MODELS Ravi Sandhu George Mason University Fairfax, Virginia USA

LATTICE-BASED MODELS Denning's axioms and lattices
Bell-LaPadula model (BLP) Integrity and information flow The Chinese Wall lattice

DENNING'S AXIOMS < SC, ,  > SC set of security classes
SC X SC flow relation (i.e., can-flow)  SC X SC -> SC class-combining operator

DENNING'S AXIOMS < SC, ,  > SC is finite
 is a partial order on SC SC has a lower bound L such that L  A for all A  SC  is a least upper bound (lub) operator on SC Justification for 1 and 2 is stronger than for 3 and 4. In practice we may therefore end up with a partially ordered set (poset) rather than a lattice.

LATTICE STRUCTURES Compartments and Categories {ARMY, NUCLEAR, CRYPTO}
{ARMY, CRYPTO} {NUCLEAR, CRYPTO} {ARMY} {NUCLEAR} {CRYPTO} {}

product of 2 lattices is a lattice
LATTICE STRUCTURES Hierarchical Classes with Compartments {A,B} TS {A} {B} S {} product of 2 lattices is a lattice

LATTICE STRUCTURES TS, {A,B} Hierarchical Classes with Compartments
{} S, {A,B} S, {A} S, {B} S, {}

SMITH'S LATTICE TS-AKLQWXYZ TS-KLX TS-KY TS-KQZ TS-KL TS-W TS-X TS-X
TS-Q TS-Z TS-L TS-K TS-Y S-LW S-L TS S-W S-A S SMITH'S LATTICE C U

SMITH'S LATTICE With large lattices a vanishingly small fraction of the labels will actually be used Smith's lattice: 4 hierarchical levels, 8 compartments, therefore number of possible labels = 4*2^8 = 1024 Only 21 labels are actually used (2%) Consider 16 hierarchical levels, 64 compartments which gives 10^20 labels

EMBEDDING A POSET IN A LATTICE
{A,B,C,D} {A,B,C} {A,B,D} {A,B,C} {A,B,D} {A,B} {A} {B} {A} {B} such embedding is always possible {}

SIMPLE-SECURITY Subject S can read object O only if label(S) dominates label(O) information can flow from label(O) to label(S) STAR-PROPERTY Subject S can write object O only if label(O) dominates label(S) information can flow from label(S) to label(O)

BLP MODEL Top Secret Secret Confidential Unclassified dominance 
can-flow

DYNAMIC LABELS IN BLP Tranquility (most common): SECURE
label is static for subjects and objects High water mark on subjects: SECURE label is static for objects label may increase but not decrease for subjects High water mark on objects: INSECURE label is static for subjects label may increase but not decrease for objects

BIBA MODEL High Integrity Some Integrity Suspicious Garbage dominance
can-flow

BIBA MODEL SIMPLE-INTEGRITY STAR-PROPERTY
Subject S can read object O only if label(O) dominates label(S) information can flow from label(O) to label(S) STAR-PROPERTY Subject S can write object O only if label(S) dominates label(O) information can flow from label(S) to label(O)

EQUIVALENCE OF BLP AND BIBA
HI (High Integrity) LI (Low Integrity) LI (Low Integrity) HI (High Integrity) BIBA LATTICE EQUIVALENT BLP LATTICE

EQUIVALENCE OF BLP AND BIBA
HS (High Secrecy) LS (Low Secrecy) LS (Low Secrecy) HS (High Secrecy) BLP LATTICE EQUIVALENT BIBA LATTICE

COMBINATION OF DISTINCT LATTICES
HS HI HS, LI HS, HI LS, LI LS LI LS, HI BLP BIBA GIVEN EQUIVALENT BLP LATTICE

BLP AND BIBA BLP and Biba are fundamentally equivalent and interchangeable Lattice-based access control is a mechanism for enforcing one-way information flow, which can be applied to confidentiality or integrity goals We will use the BLP formulation with high confidentiality at the top of the lattice, and high integrity at the bottom

LIPNER'S LATTICE S: System Managers O: Audit Trail S: System Control
S: Application Programmers O: Development Code and Data S: Repair S: Production Users O: Production Data S: System Programmers O: System Code in Development O: Repair Code O: Production Code O: Tools LEGEND S: Subjects O: Objects O: System Programs

LIPNER'S LATTICE Uses 9 labels from a possible space of 192 labels
Audit trail is at lowest integrity Production users are only allowed to execute production code System control subjects are allowed to write down (with respect to confidentiality) or equivalently write up (with respect to integrity)

CHINESE WALL POLICY Example of a commercial security policy for confidentiality Mixture of free choice (discretionary) and mandatory controls Introduced by Brewer-Nash in Oakland '89

CONFLICT OF INTEREST CLASSES
CHINESE WALL EXAMPLE ALL OBJECTS CONFLICT OF INTEREST CLASSES OIL COMPANIES BANKS A B X Y COMPANY DATASETS A consultant can access information about at most one company in each conflict of interest class

O is in the same company dataset as some object previously read by S (i.e., O is within the wall) or O belongs to a conflict of interest class within which S has not read any object (i.e., O is in the open)

WRITE ACCESS BREWER-NASH STAR-PROPERTY S can write O only if
S can read O by the simple security rule and no object can be read which is in a different company dataset to the one for which write access is requested

REASON FOR BN STAR-PROPERTY
ALICE'S WALL BOB'S WALL Bank A Bank B Oil Company X Oil Company X cooperating Trojan Horses can transfer Bank A information to Bank B objects, and vice versa, using Oil Company X objects as intermediaries

IMPLICATIONS OF BN STAR-PROPERTY
Either S cannot write at all or S is limited to reading and writing one company dataset

WHY THIS IMPASSE? Failure to clearly distinguish user labels from subject labels.

CHINESE WALL LATTICE SYSHIGH A, X A, Y B, X B, Y
The high water mark of a user's principal can float up so long as it remain below SYSHIGH A, - -, X -, Y B, - SYSLOW

USERS, PRINCIPALS, SUBJECTS
ALICE.BANK A & OIL COMPANY X ALICE.OIL COMPANY X ALICE ALICE.BANK A ALICE.nothing USER PRINCIPALS

USERS, PRINCIPALS, SUBJECTS
JOE.TOP-SECRET JOE.SECRET JOE JOE.CONFIDENTIAL JOE.UNCLASSIFIED USER PRINCIPALS

USERS, PRINCIPALS, SUBJECTS
The Bell-LaPadula star-property is applied not to Joe but rather to Joe's principals Similarly, the Brewer-Nash star-property applies not to Alice but to Alice's principals

CONCLUSION So long as Denning’s axioms are satisfied we will get a lattice-based information flow policy One-directional information flow in a lattice can be used for secrecy as well as for integrity but does not solve either problem completely To properly understand and enforce Information Security policies we must distinguish between policy applied to users, and policy applied to principals and subjects

REFERENCES Ravi Sandhu, "Lattice-Based Access Control Models."
IEEE Computer, November 1993, pages 9-19