Bài giảng Bảo mật cơ sở dữ liệu: Chương 3 - Trần Thị Kim Chi (tt)

Bài giảng Bảo mật cơ sở dữ liệu - Chương 3: Bảo mật theo cơ chế MAC cung cấp cho người học các kiến thức: Define Mandatory Access Control Models, secrecy-preserving models, integrity-preserving models, multi-Level security, multi-level databases access control models,... Mời các bạn cùng tham khảo.

Bảo mật theo cơ chề MAC

Mandatory Access Control Models

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

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xx Mandatory Access Control : A system-wide policy

decrees who 1s allowed to have access; individual user cannot alter that access

** Relies on the system to control access

Mandatory Access Control vs Discretionary Access Control

%x 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

%x DAC, which also governs the ability of subjects to access objects, allows users the ability to make policy decisions and/or assign security attributes

%x MAC-enabled systems allow policy administrators to implement organization-wide security policies

%x 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

Degrees of MAC system strength

%x 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 1s 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 1s 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 benchmar

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Evaluation of MAC system strength

¥x 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] 1s 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,

Definition and need for MLS

%x Multilevel security involves a database in which

the data stored has an associated classification and consequently constraints for their access

*x MLS allows users with different classification

levels to get different views from the same data

*x MLS cannot allow downward leaking, meaning

that a user with a lower classification views data stored with a higher classification

Definition and need for MLS

%x Usually multilevel systems are with the federal

government

%x Some private systems also have multilevel security needs

3x MLS relation is split into several single-level relations,

A recovery algorithm reconstructs the MLS relation from the decomposed single-level relations

Sx At times MLS updates cannot be completed because it would result in leakage or destruction of secret

information

Definition and need for MLS

*< In relational model, relations are tables

and relations consist of tuples (rows) and

Starship Objective Destination

Definition and need for MLS

x The relation in the example has no

classification associated with it ina relational model

x The same example in MLS with

classification will be as follows:

Starship Objective Destination

Enterprise U Voyager U Exploration Spying S U Mars Talos U S

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

x Bell — LaPadula Model

xx Biba Model

Bell — LaPadula Model

%x 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

*x This model is the most widely recognized Access Matrix model with classified data

The model deal with confidentiality only

Bell — LaPadula Model

Two properties: No read up and No write down

xx Simple security property: Subject A is allowed to read object O only if class(O) class(A)

*_nroperty: Subject A is allowed to write object

O only if class(A) class(Q)

k

Xš The *-property was Bell and LaPadulaˆs 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

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

Bell — LaPadula Model

% An access class cl dominates > an access class

c2 iff

- Security level of cl is greater than or equal to that of c2

- The categories of cl include those of c2

S,{ Nuclear}

Bell — LaPadula Model

** Bell-LaPadula model is based on a subject- object paradigm

* Subjects are active elements of the system that execute actions

x 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)

Bell — LaPadula Model

** Subjects execute access modes on objects

x Access modes are:

- Read-only

- Append (writing without reading)

- Execute

- Read-write (writing known data)

* Decentralized administration of privileges

on objects

Bell — LaPadula Model

¥x Control direct and indirect flows of information

%x Prevent leakage to unauthorized subjects

%x User can connect to the system with any access class dominated by their clearance

S,{ Nuclear}

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

No-read-up & No-write-down

OBJECTS

=" Can TS subject write to S object?

=" Can S subject write to U object?

= How to apply to the Trojan Horse case?

Solution to Trojan Horse

** Possible classification reflecting the access

restrictions:

- Secret for Vicky and “Market”

- Unclassified to John and “Stolen”

xx If Vicky connect to system as secret, write is blocked

xx If Vicky connects to system as unclassified, read

is blocked

x Is Vicky allowed to write to the unclassified object? How’?

Applying BLP: An Example

xx Alice has (Secret, {NUC, EUR}) clearance

xx 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’’)

xx Alice is a user, and she can login with a different

ID (as a different principle) with reduced clearance

- Alias] (Secret, {NUC, EUR})

- Alias2 (Secret, {EUR})

Bell — LaPadula Model

xT wo 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

Bell — LaPadula Model

x 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

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

The Biba Model

XA model due to Ken Biba which is often referred to as

“Bell-LaPadula upside down.”

%x It deals with integrity alone and ignores confidentiality entirely

%x Biba model covers integrity levels, which are analogous to sensitivity levels in Bell-LaPadula

%x Integrity levels cover inappropriate modification of data

%x Prevents unauthorized users from making modifications

(1st goal of integrity)

The Biba Model

Xš Each subject and object in the system is assigned an integrity classification

- Crucial

— Important

Integrity Level

x 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

* 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

Applying Mandatory Policies to Databases

** Commercial DBMSs Oracle, Sybase, and TruData have MLS versions

of their DBMS

¥m Because of Bell-LaPadula restrictions, subjects having different

clearances see different versions of a multilevel relation

[NamelAn| Dept |Àp|Salary|As[ {Name]\An|Dept]A\p|Salary},s|

Bob | U |]Depti] U} 100K {U Bob | U J|Dept1[ U | 100k EU Jim Ƒ U |Deptl{ U | 100K EU Jim Ƒ U |Deptl| U | 100k EU

Polyinstantiation

** Request by low level subject

- An unclassified subject request insert of <Ann, Deptl, 1OOK>

%x If this update is rejected, then the user would be able to infer something about Ann

%x MLS would allow the secret channel to permit data update and protect data integrity

5

Polyinstantiation

X Request by high level subjects

- A secret subject request to insert <Bob, Dept2, 200K>

- Inform the subject of the conflict and refuse the

im | U |Depti}] U} 100 Jim | U |Depti] U] 100K

nn ept2 200 Sam | U JDept1{ U =

(a)

Challenges

* Cover Stories

- Non-true data to hide the existence of the actual value

- Not released is a cause of information leakage

x Fine-grained is not easy

- Aggregation, association

- Block inference channels

Covert Channels

3x 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

Covert Channels (conf ` d)

Xš Other Examples for Covert Channels:

- Timing Channels

- Resource State

- Hidden Information in downgraded documents

%x 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

Multilateral Security

%x Instead of the information flow-control boundaries being

horizontal, as in the MLS model, we instead need the

boundaries to be the mostly vertical

responsible for spying on another

%x Also known as compartmentation

Multilateral Security

%x Multilateral security models:

- The Chinese Wall Model

- The BMA Model (British Medical Association)

Chinese Wall Model

x Conflict of interest to accept, because his

advice for either bank would affect his advice to the other bank

Organization

x Organize entities into “conflict of interest”

classes

x Control subject accesses to each class

x Control writing to all classes to ensure

information is not passed along in violation

of rules

x Allow sanitized data to be viewed by everyone