Li Xiong CS573 Data Privacy and Security Access Control

What is Access Control? Security Engineering by Ross Anderson, 2001 Its function is to control which principles (persons, processes, machines, …) have access to which resources in the system – which files they can read, which programs they can execute, and how they share data with other principles, and so on. Access control is pervasive OS (unix, windows), databases, Java

Night Club Example Authentication ID Check Access Control Over 18 - allowed in Over 21 - allowed to drink On VIP List - allowed to access VIP area Enforcement Mechanism Walls, Doors, Locks, Bouncers

Access control and other security services Identification and Authentication – establishing and verifying the identity of the user Something you know, such as a password or a personal identification number (PIN). Something you have, such as a smart card or security token. Something you are, such as fingerprint, voice, retina, or iris characteristics. Where you are, for example on or off campus, inside or outside a company firewall Access control determines which subject can access what resources after identification and authentication

Access control and other security services Enforcement mechanisms Auditing – posteriori analysis of all the requests and activities of users in the system Deterrent – users may be discouraged from attempting violations Means to analyze users behavior to detect possible violations

Access control and other security services

Access control Access control mechanisms – low level software functions that can be used to implement a policy Access matrix model Implementation approaches Access control policies – high level guidelines that determine how accesses are controlled Discretionary access control (DAC) Mandatory access control (MAC) Role based access control (RBAC) Attribute based access control (ABAC)

Access Matrix Model A set of subjects S A set of objects O A set of rights R An access control matrix One row for each subject One column for each subject/object Elements are right of subject on an another subject or object

Access matrix

Implementation approaches Access control lists (ACLs) Capabilities Authorization relation or table

Access control lists (ACLs) Each object is associated with an ACL Storing the matrix in columns Modern OS typically take the ACL approach

Capabilities Each subject is associated with a capability list Storing the matrix in rows

Authorization relation Each row, or tuple, specifies one access right of a subject to an object Relational databases typically use it

Access control Access control mechanisms – low level software functions that can be used to implement a policy Access matrix model Implementation approaches Access control policies – high level guidelines that determine how accesses are controlled Discretionary access control (DAC) Mandatory access control (MAC) Role based access control (RBAC)

Discretionary AC Name Access Tom Yes John No Cindy Yes Application Access List Restricts access to objects based solely on the identity of users who are trying to access them No restrictions on information flow Individuals Resources database 1 database 3 database 2

Mandatory AC Governs access based on the classification of subjects and objects Assign a security level to all information – sensitivity of information Assign a security level to each user – security clearance Military and government: Top secret (TS) > secret (S) > confidential (C) > unclassified (U) Access principles Read Down – a subject’s clearance must dominate the security level of the object being read Write Up – a subject’s clearance must be dominated by the security level of the object being written

Mandatory AC (cont) IndividualsResources/Information Database 1 DS Database 3 C Database 2 S Write up Read down TS C S U Information can only flow upwards or within the same class

Role-Based AC Governs the access based on roles Access authorizations on objects are specified for roles Users are given authorizations to adopt roles A user has access to an object based on the roles

Role-Based AC IndividualsRolesResources Role 1 Role 2 Role 3 Database 1 Database 3 Database 2 User’s change frequently, Roles don’t

Role-based Access Control Benefits Authorization management – assigning users to roles and assigning access rights to roles Hierarchical roles – Inheritance of privileges based on hierarchy of roles Least privilege – allow a user to sign on with least privilege required for a particular task Separation of duties – no single user should be given enough privileges Object classes – objects can be grouped based on classifications

RBAC Reference Model (Sandhu ‘96) RBAC0, minimum requirement RBAC1, RBAC0 + role hierarchies RBAC2, RBAC0 + constraints RBAC3, RBAC1 + RBAC2 ModelsHierarchiesConstraints RBAC 0 No RBAC 1 YesNo RBAC 2 NoYes RBAC 3 Yes

user_sessionssession_roles (UA) User Assign- ment (PA) Permission Assignment USERSOBSOPS SESSIONS ROLES PERMISSIONS Core RBAC System

USERS Process Person Intelligent Agent

ROLES Developer Budget Manager Help Desk Representative A role is a job function with some associated semantics regarding responsibility and authority (permissions). Director MTM relation between USERS & PRMS

Permissions SQL A permission is an approval of a particular access to one or more objects Database – Update Insert Append Delete Locks – Open Close Reports – Create View Print Applications - Read Write Execute

UA (user assignment) A user can be assigned to one or more roles Developer USERS set ROLES set Help Desk Rep A role can be assigned to one or more users

PA (permission assignment) A prms can be assigned to one or more roles Admin.DB1 PRMS set ROLES set A role can be assigned to one or more prms User.DB1 View Update Append Create Delete Drop

SESSIONS Each session is a mapping of one user to possibly many roles USER guest user admin invokes SQL DB1.table1 FIN1.report1 APP1.desktop SESSION

user_sessions (RH) Role Hierarchy session_roles (UA) User Assign- ment (PA) Permission Assignment USERSOBSOPS SESSIONS ROLES PERMISSIONS Role Hierarchy RBAC

Tree Hierarchies Production Engineer 1 Quality Engineer 1 Engineering Dept Production Engineer 2 Quality Engineer 2 Production Engineer 1 Project Lead 1 Quality Engineer 1 Director Production Engineer 2 Project Lead 2 Quality Engineer 2

Lattice Hierarchy Production Engineer 1 Quality Engineer 1 Engineering Dept Production Engineer 2 Quality Engineer 2 Project Lead 1 Director Project Lead 2

user_sessions (RH) Role Hierarchy session_roles (UA) User Assign- ment (PA) Permission Assignment USERSOBSOPS SESSIONS ROLES PERMISSIONS SSD DSD Constrained RBAC

Static mutual exclusion constraints Two mutually exclusive roles: cannot both have the same user as members Two mutually exclusive roles: cannot both have the same permissions Two mutually exclusive permissions: one role cannot have both permissions

Cardinality constraints On user-role assignment At most k users can belong to the role At least k users must belong to the role Exactly k users must belong to the role

Dynamic Constraints At most k users can activate the same role in one session No user is allowed to activate n or more roles in one session

Constraints with Role Hierarchies Two roles can be mutually exclusive only if neither one inherits the other If two roles are mutually exclusive, no roles can inherit from both If two roles are mutually exclusive, there can be no “root” or “super users”

Separation of Duty Constraints is a means rather than an end Separation of duty is the goal No single user possesses all the permissions needed to accomplish a sensitive task Permission assignment problem

Attribute based Access Control (ABAC) Access control decisions are made based on a set of characteristics, or attributes, associated with the requestor and/or the resource A requester provides a set of attributes, they are checked against permissible attributes E.g. a person in UltraMegaCorp tries to access an administration interface for customer data in Atlanta must present credentials with a division attribute of “customer relations division” and a title of “senior manager” and a location attribute of “Atlanta” No need for predefined list of roles or permissions

References Access control: principle and practice, Sandhu, 1994 Role-based Access Control Models, Sandhu, 1996

Coming up Hippocratic databases Fine-grained access control Policy management and enforcement