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Authorization Brian Garback. Research Issues  Authentication who are you? quantification of trust levels  Mobile devices what capabilities do you have?

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Presentation on theme: "Authorization Brian Garback. Research Issues  Authentication who are you? quantification of trust levels  Mobile devices what capabilities do you have?"— Presentation transcript:

1 Authorization Brian Garback

2 Research Issues  Authentication who are you? quantification of trust levels  Mobile devices what capabilities do you have? can wireless be as secure as wired?  Authorization given who you are, what can you do? how do we control privileges?  Federation how can trust be shared? how to cross trust domain boundaries?

3 Itinerary  History of Access Control Role-Based AC Context-Based AC Context-Aware AC Permission Based Delegation Model  Authorization Specifications CAAC WS-Policy Implementation XACML SAML  Specification-Level Goals

4 Access Control History RBAC CBAC CAAC PBDM

5 Role-Based Access Control  Sandu et al. formalized Role-Based Access Control in 1996  User U acting in role R is granted permission P  Advantage: greatly improved efficiency  Disadvantage: cannot specify fine-grained rules UserRole Permission

6 Context-Based Access Control  What is “context”? Circumstances in which an event occurs SystemSubjectObject Type Owner Name Age ID Location Time Date CPU Load

7 Context-Based Access Control RoleUser  Advantage: access control is context-aware  Disadvantage: this is still a static model Context PermissionConstraints with hasgiven

8 RBAC → CBAC → CAAC  RBAC and CBAC, even with extensions, cannot meet the access requirements of modern healthcare environments  CAAC is an extension to CBAC that is consistent with implementation via web services  CAAC permits dynamic specification and dynamic enforcement of arbitrary access rules  Context implementation is separated from the main business logic of target applications.

9 Context-Aware Access Control  Presented 2004 by Juhnze Hu  Terminology: Data Object: the smallest unit to be accessed in an application Data Type: a group of data objects with the same attributes Data Set: the set of all data objects User Set: the set of potential entities that access the data objects

10 Definition 1: Context Type A context type is defined as a property related to every participant in an application when it is running. Context Set: a set of all context types in an application. CS = {CT 1, CT 2 … CT n }, 1  i  n. Context Implementation: a function of context types defined by CI: CT 1  CT 2  …  CT n  CT, n  0

11 Definition 2: Context Constraint We define a context constraint as a regular expression as follows: Context Constraint := Clause 1  Clause 2 …  Clause i Clause := Condition 1  Condition 2 …  Condition i Condition := CT is an element of CS OP is a logical operator in set {>, , , , , =} VALUE is a specific value of CT

12 Definition 3: Authorization Policy An authorization policy as a triple, AP = (S, P, C) where: S: the subject in this policy, which could be a user or a role P: the permission in this policy, which is defined as a pair, where M is an operation mode defined in {READ, APPEND, DELETE, UPDATE} and O is a data object or data type C: is a context constraint in this policy

13 Definition 4: Data Access We define data access as a triple, DA = (U, P, RC) where: U: a user in the User Set who issues this data access P: the permission this user wants to acquire RC: the runtime context, a set of values for every context type in the Context Set DA (U, P, RC) is granted iff there exists an AP (S, P, C) st 1. U  S && 2. P = P && 3. C is evaluated as true under RC

14 CAAC Authorization Policy givenhas S: user or role P: permission C: constraint Clause 1 Clause n ……  condition ……  context type context implementation A predicate of Evaluated by

15 2004 Security Infrastructure

16 Quick Review  RBAC  CBAC  CAAC: dynamic specification and dynamic enforcement of arbitrary access rules separation of context implementation and the main business logic of target applications. UserRole Permission RoleUser Context PermissionConstraints assignedhasgiven assignedgranted

17 Permission Based Delegation Model  2003: Zhang at GMU  Given RBAC as an AC model  Delegation of authority is common Need-to-know Separation of duty Rotation of sensitive job position  Delegation involves 1. Backup of role 2. Decentralization of authority 3. Collaboration of work

18 Delegation History  RBDM0: human → human Delegator delegates role membership to a delegatee  RDM2000: Role delegation in a role hierarchy and multi-step delegation  Unit of delegation is a ROLE!  PBDM Supports role and permission level delegation

19 RBDM Shortcomings

20 Permission Based Delegation  PBDM0 Summary: Multi-step temporal delegation Two role types:  Regular Roles (RR)  Temporary Delegation Roles (DTR) Multi-step delegation and revocation  Drawbacks: 1. No delegation limitations (risky) 2. No role-hierarchy

21 PBDM0 > RBDM 1. John creates “D1” 2. John assigns:  permission “change_schedule” to D1 (permission-role)  role “PE” to D1 (role-role) 3. John assigns Jenny to D1 (user-role)

22 Permission Based Delegation  PBDM0 Summary: Multi-step temporal delegation Two role types:  Regular Roles (RR)  Temporary Delegation Roles (DTR) Multi-step delegation and revocation  Drawbacks: 1. No admin delegation limitations (risky) 2. No role-hierarchy

23 PBDM1  Role-layers: 1. Regular Roles (RR)  cannot be delegated to other roles or users 2. Delegatable Roles (DBR)  permissions can be delegated 3. Delegation Roles (DTR)  created by delegatable roles  Each user has (RR, DBR) pair = RR in PBDM0  Solves admin issue: Administrative assignment of permissions to roles

24 PBDM1 Example 1. John creates a DTR “D2” 2. John assigns “change schedule” to D2 from PL’ “PE’” to D2 3. John assigns Jenny to D2

25 PBDM1 Revocation  Individual user can: 1. Remove a user from delegatees 2. Remove parts from the delegation role  Admin can: 1. Move permissions from DBR to RR 2. Revoke a user from RR or DBR

26 PBDM2 > PBDM1 0 & 1 cannot support role-to-role delegation 2 does with multi-step delegation and multi- option revocation features

27 PDBM2 Overview Four layers: 1. Regular roles (RR) 2. Fixed delegatable roles (FDBR) owns a set of DTRs which form a role hierarchy 3. Temporal delegatable roles (TDBR) has no role hierarchy can receive permissions delegated by a FDBR (role-to-role deleg.) 4. Delegation roles (DTR) owned by a FDBR RR and FDBR: the same as RR and DBR in PDBM1 have role hierarchies

28 PDBM2 Rules and Example Delegation authority handled by admin No individual user can own a DTR or permission Scenario: D3 created based on PL’ and delegated to QE’’ 1. Create a delegation role D3 2. Assign: permission change_schedule to D3 FDBR PE’ to D3 3. Assign D3 to TDBR QE’’

29 PBDM2 Architecture D3 created based on PL’ and delegated to QE’’ 1. Create a delegation role D3 2. Assign: permission change_schedule to D3 FDBR PE’ to D3 3. Assign D3 to TDBR QE’’

30 PBDM2 Revocation  Contains PBDM1’s security admin  PBDM2 has options in the role layer: 1. Remove pieces of permissions from a delegation role 2. Revoke a DTR owned by a FBDR 3. Remove pieces of permissions from a FBDR to a RR

31 PBDM Comparison  RBDM: Ambiguity btw admin and delegation  PBDM: supports role and permission level delegation Partial revocation is also possible

32 Authorization Specifications WS-Policy XACML SAML

33 Policy Specification  Security policies must be exchangeable across domains Prescription accepted Requested License Policy response Send prescription HospitalPharmacy

34 Policy Specification  There are several XML-based policy languages WS-Policy (from Microsoft) XACML (eXtensible Access Control Markup Language) SAML (Security Assertion Markup Language) In CAAC, WS-Policy was chosen as the specification language because it is inherently supported in the Microsoft.NET framework.

35 WS-Policy Overview  Why: To describe service requirements, preferences, and capabilities of web services  Goal: Provide the general purpose model and syntax to describe and communicate the policies of a Web service  What: Provides a flexible and extensible grammar for expressing the capabilities, requirements, and general characteristics of Web Services

36 CAAC Policy Specification  Our customized WS-Policy tags For any authorization policy AP = (S, P, C) specifies the data object or data type of permission P specifies the operation mode of permission P specifies the permission P in an AP specifies the security token issued to S specifies one context condition in C specifies which context type is used in one context condition of C

37 A Sample Policy PatientRecord Delete DeletePatientRecord Medical Records Staff Trust Level

38 XACML  OASIS standard version 1.1 (2.0 and 3.0)  Policy language  Access control decision request/response language

39 XACML - Policies  Policy Set: container of policies (local and remote)  Policy: a set of rules  Rule: a target, effect, and condition  Target: a resource, subject, and action  Effect: results of rule; “Permit” or “Deny”  Condition: Boolean; “True,” “False,” or “Indeterminate”

40 XACML – Access Control  Reconciles Multiple policies Multiple rules per policy Multiple control decisions  Use a combining algorithm to combine multiple decisions into a single decision  Use standard or customized algorithms  Policy Combining Algorithms—used by PolicySet  Rule Combining Algorithms—used by Policy

41 XACML – Policy Evaluation  Obtain attributes from subject  Compare obtained attributes with attributes accepted by the policy  Evaluate conditions using standard or customized functions  E.g. The function [type]-one-and-only looks in a “bag” of attribute values and returns the single value if there is one or an error if there are zero or multiple.

42 XACML Data Flow

43 SAML assertions  An assertion is a declaration of facts about a subject  SAML has three kinds, all related to security: 1. Authentication 2. Attribute 3. Authorization decision  You can extend SAML to make your own kinds of assertions

44 SAML conceptual model

45 Some common information in all assertions  Issuer and issuance timestamp  Assertion ID  Subject Name plus the security domain Optional subject confirmation, e.g. public key  “Conditions” under which assertion is valid SAML clients must reject assertions containing unsupported conditions Special kind of condition: assertion validity period  Additional “advice” E.g., to explain how the assertion was made

46 Authentication assertion  An issuing authority asserts that: subject S was authenticated by means M at time T  Caution: Actually checking or revoking of credentials is not in scope for SAML!  It merely lets you link back to acts of authentication that took place previously

47 Example authentication assertion

48 Attribute assertion  An issuing authority asserts that: subject S is associated with attributes A, B, C… with values “a”, “b”, “c”…  Typically this would be gotten from an LDAP repository “jim” in “virginia.edu” is associated with attribute “Department” with value “Computer Science”

49 Example attribute assertion Computer Science

50 Authorization decision assertion  An issuing authority decides whether to grant the request: by subject S for access type A to resource R given evidence E  The subject could be a human or a program  The resource could be a web page or a web service, for example

51 Example authorization decision assertion 

52 SAML conceptual model

53 XACML & SAML  XACML & SAML are counterparts XACML handles the access control policies and decisions SAML handles the actual communication of authentication and authorization requests and responses  E.g. SAML used to assert authentication and authorization attributes XACML uses these assertions and evaluates the policies to come to a decision

54 Research Questions  Dynamic interfaces per permission/role  Permission management for subobjects  Secondary role issues: Constrained hierarchical roles Permission-level constrained delegation Revocation  Delegation extensions to XACML & SAML  Provide an access control interface


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