1. Bảo mật theo cơ chế MAC Mandatory Access Control Models

2. Agenda Define Mandatory Access Control Models
Secrecy-preserving models
Integrity-preserving models
Multi-Level security
Multi-level databases access control models
Multi-level secure DBMS architecture
MAC trong các hệ QTCSDL thông dụng

3. Define Mandatory Access Control
Mandatory Access Control : A system-wide policy decrees who is allowed to have access; individual user cannot alter that access.
Relies on the system to control access.
Examples:
The law allows a court to access driving records without the owners’ permission.
Traditional MAC mechanisms have been tightly coupled to a few security models.
Recently, systems supporting flexible security models start to appear (e.g., SELinux, Trusted Solaris, TrustedBSD, etc.)

4. Mandatory Access Control vs Discretionary Access Control
MAC is centrally controlled by a security policy administrator; users do not have the ability to override the policy and, for example, grant access to files that would otherwise be restricted.
DAC, which also governs the ability of subjects to access objects, allows users the ability to make policy decisions and/or assign security attributes.
MAC-enabled systems allow policy administrators to implement organization-wide security policies.
With DAC, users cannot override or modify this policy, either accidentally or intentionally. This allows security administrators to define a central policy that is guaranteed (in principle) to be enforced for all users.

5. Degrees of MAC system strength
In some systems, users have the authority to decide whether to grant access to any other user. To allow that, all users have clearances for all data. This is not necessarily true of a MAC system. If individuals or processes exist that may be denied access to any of the data in the system environment, then the system must be trusted to enforce MAC. Since there can be various levels of data classification and user clearances, this implies a quantified scale for robustness. For example, more robustness is indicated for system environments containing classified Top Secret information and uncleared users than for one with Secret information and users cleared to at least Confidential. To promote consistency and eliminate subjectivity in degrees of robustness, an extensive scientific analysis and risk assessment of the topic produced a landmark benchmark standardization quantifying security robustness capabilities of systems and mapping them to the degrees of trust warranted for various security environments. The result was documented in CSC-STD [6] Two relatively independent components of robustness were defined: Assurance Level and Functionality. Both were specified with a degree of precision that warranted significant confidence in certifications based on these criteria.

6. Evaluation of MAC system strength
The Common Criteria[7] is based on this science and it intended to preserve the Assurance Level as EAL levels and the functionality specifications as Protection Profiles. Of these two essential components of objective robustness benchmarks, only EAL levels were faithfully preserved. In one case, TCSEC level C2[8] (not a MAC capable category) was fairly faithfully preserved in the Common Criteria, as the Controlled Access Protection Profile (CAPP).[9] Multilevel security (MLS) Protection Profiles (such as MLSOSPP similar to B2)[10] is more general than B2. They are pursuant to MLS, but lack the detailed implementation requirements of their Orange Book predecessors, focusing more on objectives. This gives certifiers more subjective flexibility in deciding whether the evaluated product’s technical features adequately achieve the objective, potentially eroding consistency of evaluated products and making it easier to attain certification for less trustworthy products. For these reasons, the importance of the technical details of the Protection Profile is critical to determining the suitability of a product.
Such an architecture prevents an authenticated user or process at a specific classification or trust-level from accessing information, processes, or devices in a different level. This provides a containment mechanism of users and processes, both known and unknown (an unknown program (for example) might comprise an untrusted application where the system should monitor and/or control accesses to devices and files).

7. Multilevel Security (MLS)
Definition and need for MLS
Security Classification
Secrecy-Based Mandatory Policies: Bell-LaPadula Model
Integrity-based Mandatory Policies: The Biba Model
Limitation of Mandatory Policies
Hybrid Policies
The Chinese Wall Policy

8. Definition and need for MLS
Multilevel security involves a database in which the data stored has an associated classification and consequently constraints for their access
MLS allows users with different classification levels to get different views from the same data
MLS cannot allow downward leaking, meaning that a user with a lower classification views data stored with a higher classification

9. Definition and need for MLS
Usually multilevel systems are with the federal government
Some private systems also have multilevel security needs
MLS relation is split into several single-level relations, A recovery algorithm reconstructs the MLS relation from the decomposed single-level relations
At times MLS updates cannot be completed because it would result in leakage or destruction of secret information

10. Definition and need for MLS
In relational model, relations are tables and relations consist of tuples (rows) and attributes (columns)
Example:
Consider the relation
SOD(Starship, Objective, Destination)
Starship
Objective
Destination
Enterprise
Voyager
Exploration
Spying
Talos
Mars

11. Definition and need for MLS
The relation in the example has no classification associated with it in a relational model
The same example in MLS with classification will be as follows:
Starship
Objective
Destination
Enterprise U
Voyager U
Exploration U
Spying S
Talos U
Mars S

12. Definition and need for MLS
In MLS, access classes can be assigned to:
Individual tuple in a relation
Individual attribute of a relation
Individual data element of tuples in a relation
Bell – LaPadula Model
Biba Model

13. Bell – LaPadula Model
Proposed by David Bell and Len Lapadula in 1973, in response to U.S. Air Force concerns over the security of time-sharing mainframe systems.
This model is the most widely recognized Access Matrix model with classified data
The model deal with confidentiality only.
This model has two components:
Classification
Set of categories
Bell-LaPadula model shows how to use Mandatory Access Control to prevent the Trojan Horse

14. Bell – LaPadula Model Two properties: No read up and No write down.
Simple security property: Subject A is allowed to read object O only if class(O) class(A).
*-property: Subject A is allowed to write object O only if class(A) class(O).
The *-property was Bell and LaPadula’s critical innovation. It was driven by the fear that a user with “Secret” clearance might be “tricked” by attackers (e.g., through Trojan horse programs or software vulnerabilities) to copy down the information to a ”Unclassified” area where the attackers can read.

15. Bell – LaPadula Model Classification has four values {U, C, S, TS}
U = unclassified
C = confidential
S = secret
TS = top secret
Classifications are ordered: TS > S > C > U
Set of categories consists of the data environment and the application area, i.e., Nuclear, Army, Financial, Research
Example: In USA, a “SECRET” clearance involves checking FBI fingerprint files.

16. Bell – LaPadula Model
An access class c1 dominates ≥ an access class c2 iff
Security level of c1 is greater than or equal to that of c2
The categories of c1 include those of c2

17. Bell – LaPadula Model
Bell-LaPadula model is based on a subject-object paradigm
Subjects are active elements of the system that execute actions
Objects are passive elements of the system that contain information
Subjects act on behalf of users who have a security level associated with them (indicating the level of system trust)

18. Bell – LaPadula Model Subjects execute access modes on objects
Access modes are:
Read-only
Append (writing without reading)
Execute
Read-write (writing known data)
Decentralized administration of privileges on objects

19. Bell – LaPadula Model Control direct and indirect flows of information
Prevent leakage to unauthorized subjects
User can connect to the system with any access class dominated by their clearance

20. Two Principles To protect information confidentiality
No-read-up, a subject is allowed a read access to an object only if the access class of the subject dominate the access class of the object
No-write-down, a subject is allowed a write access to an object only if the access class of the subject is dominated by the access class of the object

21. No-read-up & No-write-down
Can TS subject write to S object?
Can S subject write to U object?
How to apply to the Trojan Horse case?

22. Solution to Trojan Horse
Possible classification reflecting the access restrictions:
Secret for Vicky and “Market”
Unclassified to John and “Stolen”
If Vicky connect to system as secret, write is blocked
If Vicky connects to system as unclassified, read is blocked
Is Vicky allowed to write to the unclassified object? How?

23. Applying BLP: An Example
Alice has (Secret, {NUC, EUR}) clearance
David has (Secret, {EUR}) clearance
David can talk to Alice (“write up” or “read down”)
Alice cannot talk to David (“read up” or “write down”)
Alice is a user, and she can login with a different ID (as a different principle) with reduced clearance
Alias1 (Secret, {NUC, EUR})
Alias2 (Secret, {EUR})

24. BLP: Problem
If I can write up, then how about writing files with blanks?
Blind writing up may cause integrity problems, but not a confidentiality breach

25. Bell – LaPadula Model
Two main properties of this model for a secure system are:
Simple security property
Star property
Simple security means: A subject may have read or write access to an object only if the clearance of the subject dominates the security level of the object

26. Bell – LaPadula Model Star property means: An untrusted subject may:
append if object security dominates subject security
write if object security equals subject security
read if object security is less than subject security
This model guarantees secrecy by preventing unauthorized release of information
This model does not protect from unauthorized modification of information

27. Key Points Confidentiality models restrict flow of information
Bell-LaPadula (BLP) models multilevel security
Cornerstone of much work in computer security
Simple security property says no read up and
Star property says no write down
Both ensure information can only flow up

28. The Biba Model
A model due to Ken Biba which is often referred to as “Bell-LaPadula upside down.”
It deals with integrity alone and ignores confidentiality entirely.
Biba model covers integrity levels, which are analogous to sensitivity levels in Bell-LaPadula
Integrity levels cover inappropriate modification of data
Prevents unauthorized users from making modifications (1st goal of integrity)

29. The Biba Model Two properties:
Simple Integrity Property: A low integrity subject will not write or modify high integrity data.
*-Property: The high integrity subject will not read low integrity data.
Read Up, Write Down - Subjects cannot read objects of lesser integrity, subjects cannot write to objects of higher integrity
Each subject and object in the system is assigned an integrity classification
Crucial
Important
Unknown

30. Integrity Level
Integrity level of a user reflects user’s trustworthiness for inserting, modifying, or deleting information
Integrity level of an object reflects both the degree of trust that can be placed on the info stored in the object, and the potential damage could result from unauthorized modification of info

31. Two principles
No-read-down: A subject is allowed a read access to an object only if the access class of the object dominates the access class of the subject
No-write-up: A subject is allowed a write access to an object only if the access class of the subject is dominated by the access class of the object

32. Q: How to control both the secrecy and integrity?

33. Applying Mandatory Policies to Databases
Commercial DBMSs Oracle, Sybase, and TruData have MLS versions of their DBMS
Because of Bell-LaPadula restrictions, subjects having different clearances see different versions of a multilevel relation
Visible to a user with unclassified level.
Visible to a user with secret level.

34. Polyinstantiation Request by low level subject
An unclassified subject request insert of <Ann, Dept1, 100K>
If this update is rejected, then the user would be able to infer something about Ann
MLS would allow the secret channel to permit data update and protect data integrity
Visible to a user with secret level.
Visible to a user with unclassified level.

35. Polyinstantiation Request by high level subjects
A secret subject request to insert <Bob, Dept2, 200K>
Inform the subject of the conflict and refuse the insertion (no)
Overwrite the existing tuple (no)

36. Challenges Cover Stories Fine-grained is not easy
Non-true data to hide the existence of the actual value
Not released is a cause of information leakage
Fine-grained is not easy
Aggregation, association
Block inference channels

37. Covert Channels
A covert channel is an information flow that is not controlled by a security mechanism.
In BLP, you could use the access control mechanism itself to construct a covert channel.
A low level subject makes an object “dummy.obj” at its own level.
Its high level accomplice either upgrades the security level of dummy.obj to high or leaves it unchanged.
Later, the low level subject tries to read dummy.obj. Success or failure of this request disclose the action of the high-level subject.
One bit of information has flown from high to low.
Failure means dummy.obj has be upgraded; success means dummy.obj has not been changed

38. Covert Channels (cont’d)
Other Examples for Covert Channels:
Timing Channels
Resource State
Hidden Information in downgraded documents
Commonly used techniques for reducing covert channels:
Reduce abusable functionality
High level processes get lowest resource allocation priority and can be preempted by low level processes.
Random delays, clock noise, randomized resource availability.
Auditing the use of known channels
Polyinstantiation

39. Multilateral Security
Instead of the information flow-control boundaries being horizontal, as in the MLS model, we instead need the boundaries to be the mostly vertical.
Examples:
In a consultant company, a person who consult for BankOne should not have access to the data of JPMC-Chase.
An intelligence organization wants to keep the names of agents working in one foreign country secret from the department responsible for spying on another.
Also known as compartmentation.

40. Multilateral Security
Multilateral security models:
The Chinese Wall Model
The BMA Model (British Medical Association)

41. Chinese Wall Model Problem:
Tony advises American Bank about investments
He is asked to advise Toyland Bank about investments
Conflict of interest to accept, because his advice for either bank would affect his advice to the other bank

42. Organization Organize entities into “conflict of interest” classes
Control subject accesses to each class
Control writing to all classes to ensure information is not passed along in violation of rules
Allow sanitized data to be viewed by everyone

43. The Chinese Wall Model
Proposed by Brewer and Nash to model access rules in a consultancy business where analysts have to make sure that no conflicts of interest arise when they are dealing with different clients.
Informally, conflicts arise because clients are direct competitors in the same market or because of the ownership of companies. Analysts have to adhere to the following security policy:
Rule: There must be no information flow that causes a conflict of interest.
Conflict of Interest (CoI) classes: indicate which companies are in competition.

44. The Chinese Wall Model Consider a consulting business
A consultant is authorized to work for any client, but some clients have secrecy and integrity requirements relative to other clients
Coca-Cola and Pespi
The Chinese Wall model enables definition of such scenarios
Only allow subjects to read data from one of the conflicted parties
Must control writing too

45. Definitions Objects: items of information related to a company
Company dataset (CD): contains objects related to a single company
Written CD(O)
Conflict of interest class (COI): contains datasets of companies in competition
Written COI(O)
Assume: each object belongs to exactly one COI class

46. Example Bank of America Citibank Bank of the W est Bank COI Class
Shell Oil
Union ’76
Standard Oil
ARCO
Gasoline Company COI Class

47. The Chinese Wall Model Read Rule: A subject S can read an object O if:
O is in the same Dataset as an object already accessed by S, or
O belongs to a CoI class from which S has not yet accessed any information.
Write Rule: A subject S can write an object O if:
S can read O according to the Read Rule, and
No object in a different company dataset (i.e., not O’s company dataset) can be read.

48. The Chinese Wall Model
In the write rule, the flow of information is comfined to its own company dataset. Without this rule, a person who can access both A and B can read the information from A and write to B; this way, another person who can access B can also access the information in A indirectly.
If this person can also access C, which is in the same CoI class as A, we have a violation.
The access restriction for both read and write can be lifted for sanitized information.

49. The Chinese Wall Model
Company Dataset: The set of objects that may belong to a company – CD(O)
Conflict of Interest Class: Datasets of companies in conflict – COI(O)
Each object has only one
Read iff (CW-Simple Security Property) Let PR(S) be the set of objects that a subject S has already read
If a subject S reads an O belonging to dataset CD, she can never read another O’ where CD(O’) is a member of COI(O) and CD(O’) is not equal CD(O)
Objects can be sanitized

50. The Chinese Wall Model What about control of writing?
Suppose CD1 and CD2 are have a conflict of interest
What if one user can read from CD3 and CD1…
And another can read from CD3 and CD2?
Now suppose either user can write to CD3
What happens?
Thus, a writer can only access objects in one dataset

51. Temporal Element
If Anthony reads any CD in a COI, he can never read another CD in that COI
Possible that information learned earlier may allow him to make decisions later
Let PR(S) be set of objects that S has already read
Bank of
America
Citibank
Bank of the West
Bank COI Class

52. CW-Simple Security Condition
s can read o iff :
s has read something in o’s dataset, and object o is in the same company datasets as the objects already access by s, that is “within the Wall”, or
s has not read any objects in o’s conflict of interest class, what s has read belongs to an entirely different conflict of interest class
Ignores sanitized data (see below)

53. Sanitization Public information may belong to a CD
As is publicly available, no conflicts of interest arise
So, should not affect ability of analysts to read
Typically, all sensitive data removed from such information before it is released publicly (called sanitization)
Add third condition to CW-Simple Security Condition:
3. o is a sanitized object

54. Writing Anthony, Susan work in same trading house
Anthony can read Bank 1’s CD, Gas’ CD
Susan can read Bank 2’s CD, Gas’ CD
If Anthony could write to Gas’ CD, Susan can read it
Hence, indirectly, she can read information from Bank 1’s CD, a clear conflict of interest

55. CW-*-Property Write access is only permitted if
Access is permitted by the CW-simple security rule, and
For all unsanitized objects o’, if s can read o’, then CD(o’) = CD(o)
Says that s can write to an object if all the (unsanitized) objects he/she can read are in the same dataset

56. Multilevel DBMSs Architecture
Trusted subject. The DBMS itself must be trusted to ensure mandatory policy
Trusted Computing Base: Data are partitioned in different databases, one for each level

57. Reference
Sushil Jajodia and Ravi S. Sandhu, Toward a Multilevel Secure Relational Model, essay 20

58. Discussion (15 min)
Customer order scenario from page 161 in the textbook
Identify the subject, actions, objects
Design the MAC

59. Lab 3 (Feb. 21)
Install Oracle Label Security & Using Oracle Label Security