Information Classification & Access Control

Background

All information is not equal Context decides the sensitivity

Even then, all information in the same sensitivity should not be revealed to the same set of people The more the sensitivity, the tighter the sharing becomes

Information sharing needs to be accountable A person knowing some information should not be able to share

it with someone else without certain controls

Thus, information access should be controlled based on the type of information and the type of people

What we will cover

Information Classification Principles and Case Studies

Types of controls Classic Models of Access Control Access controls in practice

Case Studies Windows and Linux Access Controls

Introduction

Aspects of information Classification Classification from a Legal Standpoint Responsibility for care and control of information Integrity of Information Criticality of information and systems processing

the information Simple to use and administer (ISO) Effective to determine the level of protection

required (ISO) Applied uniformly (ISO)

Initialization

To start information classification, need to understand the following What are the mission-critical or sensitive activities or

operations? Where is mission-critical or sensitive information stored? Where is this information processed? Who requires access to this information?

Based on the above a classification can be determined. Remember, Only governments have standard classification. Corporations require classifications based on need Reduce the number of classes as much as possible

ISO 27002 Suggested Classification Top Secret

Impending mergers or acquisitions, investment strategies, plans or designs

Highly Confidential Accounting information, business plans, sensitive information of

customers of banks (etc), patients' medical records Proprietary

Procedures, project plans, operational work routines, designs and specifications that define the way in which the organization operates

Internal Use Only Internal memos, internal project reports, minutes of meetings,

policy documents etc Public Documents

Press statements, annual reports, etc.

Case Study 1

Highly Confidential disclosing this data can cause severe financial, legal or

reputation damage E.g., Acquisitions data, tender details, negotiation

strategies (especially, buying strategies) Confidential

disclosing may cause financial, legal or reputation damage

E.g., employee information, salaries etc General

Internal information which is restricted for use within the company

Case Study 2

Top Secret disclosing this information can cause severe impact to the company’s

competitive advantage or business strategies. E.g., IP, Mergers etc Confidential

disclosing this information can violate privacy of individuals, reduce competitive advantage etc

Restricted information that can be given to only a subset of employees. E.g., Employee

appraisals etc Internal Use

information that is available for all company employees for usage in company’s business e.g., codes for identifying themselves to customer care etc

Public Information that can be made available to public through website, new

releases etc

Case Study 3

Confidential Red Disclosing causes severe damage to operations, result in

contractual or legal liability, loss of business partners, and/or cause severe drop in stock value.

Confidential Yellow Disclosing causes, moderate damage to the company, reveals

modus operandi of company at least sufficiently, reveals important technical or financial aspects, causes temporary drop in stock value etc.

Confidential Green disclosing might given some one business advantage, cannot be

associated with a particular product easily and has little competitive value. Mostly internal information.

Public Information such as audited results, changes in directorate etc,

information that is probably of interest to vendors, stockholders.

Case Study 4

Confidential Likely to adversely affect the company, embarrass an

individual etc. E.g., Customer health records Internal

All forms of proprietary information originated or owned by the company or entrusted to it. E.g., policies, procedures, phone directories etc

Public Information officially released for widespread disclosure

E.g., product brochures, disclaimers annual reports, employment advertising

Exercise

Consider all the previous classifications and give a detailed policy of protection for these classifications.

Consider both printed and electronic data. Stored as well as transmitted data.

For example, the document should address issues such as, How to store the data, how to use the data and how to monitor the sharing of data?

This whole exercise is called Records management

Access Control

Purpose: To limit access of data to only those individuals to whom it is necessary to carry out necessary tasks

Problems faced in access control Data falls in different classes and there are various

constraints in using, sharing and destroying the data. Need to describe appropriate models of access control that

will capture these constraints without violating any security tenets

How to ensure that the access control mechanisms we have, can address all conflicts appropriately?

Security Models and Assumptions Purpose of Security Models

To describe, study or analyze situations or associations To test a policy for completeness and consistency Document a policy Visualize and design of an implementation Check for consistency of implementation with the policy

requirements Assumptions

Access control policy is pre-defined for various users and objects

The policy is defined outside of any model

Classical Access Control Models Lattice Model Bell-LaPadula Model Denning Model Biba Model Chinese Wall Model

Lattice Model

A Mathematical structure of elements organized by a relation among using a relational operator.

A relation is a partial order if it is both transitive and antisymmetric Consider a set of elements: a, b, c and some operation < Transitive: If a < b and b < c then, a < c antisymmetric: If a<b and b<a, the a=b

Note: in a lattice every pair of elements need not be comparable. But the following hold in every lattice Upper bound: An element such that it is > for all other

elements Lower bound: An element such that it is < for all other

elements

Example

Relation is “is a factor of”

Typical relations: “reports to”, “descendant of”, “is subset of”, “is lesser than”

Bell- LaPadula Model

Defines formal model for allowable information flows in a secure system

Identifies allowable communication which maintaining secrecy Secure information flows describe acceptable connections

between subjects and objects of different levels of sensitivity. Such analysis the constructing systems that can perform

concurrent computation on data at two different sensitivity levels. For example, the same machine can process top-secret and

confidential data at the same time. The programs processing top-secret data would be prevented

from leaking top-secret data to the confidential data, and the confidential users would be prevented from accessing the top-secret data.

The Bell LaPadula model is useful as the basis for the design of systems that handle data of multiple sensitivities.

Semantics of Bell LaPadula

Considers: Subject Set: S and Object Set: O Each subject s in S and o in O has fixed

security class: C(s) : Clearance level C(o) : Classification level Ordered by a relation say “<“

The model can work for a lattice type of ordering easily, but can also work on restricted classes (i.e., classes that do not necessarily have a strict or partial ordering)

Properties

Simple Security Property: A Subject s may have read access to an object o only if C(o) < C(s) Meaning? Security class of the information must be atleast as high as the

classification of the information Star Property: A Subject s who has read access to an object o

may have write access to an object p only if C(o)<C(p) Meaning? Prevents “write-down” which occurs when a subject at a higher

level data access transfers that data to a low-level object Property requires that a person receiving information at one level

not talk with people cleared at levels lower than the level of the information

Semantics

Biba Integrity Model

Bell LaPadula model addresses secrecy and inappropriate flow of information

Integrity of Information is addressed by Biba Model Properties

Simple Integrity: s can modify object o only if I(s)> I(o) An untrusted subject who has write access to an object

reduces the integrity of that object Integrity *: If s has read access to object o with integrity

level I(o), s can have write access to object p only if I(o) > I(p) The low integrity of a source object implies low integrity for

any object based on the source object.

Specifying Access Control Policies Two conditions to be met:

The access control structure should help to express your desired access control policy

You should be able to check that your policy has been captured correctly

Some methods: Access control matrix Capabilities Access Control Lists

Access Control Matrix Conditions:

Bill.doc may be read & written by Bill while Alice has no access Edit.exe can be executed both by Alice and Bill but otherwise

they have no access Fun.com can be executed and read by both users, but only Bill

can write to the file

Bill.doc Edit.exe fun.com

Alice

Bob

-- Execute Execute, read

-Read, write execute exe, read, write

Capabilities

Alice’s capability: edit.exe:execute; fun.com:execute, read

Bill’s capability: bill.doc: read, write; edit.exe:execute; fun.com:execute, read, write

Problems? Difficult to get an overview of who has

permission to access a given object Difficult to revoke capability

Access Control Lists

ACL stores the access rights to an object with the object itself

ACL for the previous example:ACL for bill.doc: Bill: read, writeACL for edit.exe: Alice: execute; Bill: executeACL for fun.com: Alice: execute; Bill:execute, read, write

Problem?Finding and revoking a particular users access

permissions

Intermediate Controls

Access controls based on objects or subjects alone are prone to the problem of scalability and revocation Introduce intermediate layers between users and objects to

represent policies in a more manageable fashion Types of layers:

Groups and negative permissions Privileges Role-based Access Control Protection Rings

Groups and Negative Permissions Users with similar access rights are collected

in groups and groups are given permission to access objects

Negative permissions: an entry in the access control structure to prevent a user from accessing an object he would normally get by being part of a group

Privileges

Collect the right to execute certain operations in privileges, for example, operating system level operations E.g., system administration, backup, mail access

Popular Access Control Mechanisms Role-based Access Control : Roles are

created, access control is through high level data types and procedures

Discretionary Access Control : An owner is defined for each resource and the owner can decide who can be granted access to the resource

Mandatory Access Control : A system-wide policy decides who gets access to which resources

Role-Based Access Control

Roles: a role is a collection of procedures. Roles are assigned to users. A user can have more than one role and more than one user can have the same role

Procedures: procedures are ‘high-level’ access control methods with a more complex semantic than read or write. Procedures can only be applied to objects of certain datatypes.

Datatypes: each object is of a certain datatype and can be accessed only through the procedures defined for this datatype E.g., A lecturer can create a role Student, for students in

the course and assign the privilege to read course material to this role

Protection Rings

Each subject and each object is assigned a number depending on its importance E.g., 0-operating system kernel 1-operating system 2-utilities 3-user processes

Access control decision is made by comparing the subject’s and object’s numbers If a process is assigned the number i, then we say that the

process ‘runs in ring i’ Sample security policy:

a) Processes can only access objects in their own ring or in outer rings.

b) Processes can invoke subroutines only within their own ring