Introduction to Access Control and Trust Management Daniel Trivellato

04/09/2009Minor project course2 Outline Introduction to Access Control Discretionary and Mandatory Access Control Role-Based Access Control Distributed Trust Management Reputation-based TM Rule-based TM

04/09/2009Minor project course3 Authentication vs. Access Control Authentication: establishing who you are (of whether you possess a certain pseudonym) Access Control: establishing if you have the right of doing a certain action Authentication is often necessary for access control

04/09/2009Minor project course4 Outline Introduction to Access Control Discretionary and Mandatory Access Control Role-Based Access Control Distributed Trust Management Reputation-based TM Rule-based TM

04/09/2009Minor project course5 Basics: Subject, Object, Action Subjects Alice, Bob, Alice’s program Objects a file, the printer Actions read, write, execute, modify, send

04/09/2009Minor project course6 Discretionary Access Control Goal: prevent illegitimate access to resources Access is granted to users, or user groups Ownership: Users have all the rights about the objects they create Delegation: Users can grant the rights they have to others Users that have control can remove rights

04/09/2009Minor project course7 DAC Models Take-grant model Lampson (1974) Graham-Denning (1972) Harrison-Rizzo-Ullman (1976) Griffiths-Wade (1976) Originator control (1989)

04/09/2009Minor project course8 Lampson’s Access Matrix Set of objects O Set of users U Access Matrix A (UxU and UxO) Entries are sets of allowed actions (read, write, call,…) Plus owns for administration of rights * flag for delegation right

04/09/2009Minor project course9 Access Matrix - Example File 1File 2File 3Program 1 Alice owns read write read write Bobread* read write execute Charlieread execute read

04/09/2009Minor project course10 Mandatory Access Control Goal: prevent illegitimate flow (leakage) of information Attach security labels to subjects and objects Users, processes are given a clearance Objects, resources are given a label Information can not flow to lower or incomparable security classes

04/09/2009Minor project course11 MAC – Example SUBJECTSOBJECTS ……..... TS S C U Information flow TS S C U write read write read write read write read Bell-La Padula: NO READ UP NO WRITE DOWN

04/09/2009Minor project course12 Outline Introduction to Access Control Discretionary and Mandatory Access Control Role-Based Access Control Distributed Trust Management Reputation-based TM Rule-based TM

04/09/2009Minor project course13 Role-Based Access Control Users are assigned to roles Roles are assigned rights File 1File 2File 3Program 1 Tester writeread, write Programmerread, write Group memberreadexecute TesterProgrammerGroup member Alice xx Bobxx File 1File 2File 3Program 1 Alice read, write execute Bobreadread, writeexecute

04/09/2009Minor project course14 RBAC Roles can be hierarchical Rights are inherited Project leader Project member TesterProgrammer

04/09/2009Minor project course15 Outline Introduction to Access Control Discretionary and Mandatory Access Control Role-Based Access Control Distributed Trust Management Reputation-based TM Rule-based TM

04/09/2009Minor project course16 Trust Management Typical access control mechanism TM alternative authorizationsubjectID showslookup authorizationsubjectattributes hasinfers

04/09/2009Minor project course17 Distributed Trust Management Deals with authorizations in a distributed system (e.g., the Internet) need to interact with people you don’t know 2 types of DTM Reputation-based TM Rule-based TM

04/09/2009Minor project course18 Outline Introduction to Access Control Discretionary and Mandatory Access Control Role-Based Access Control Distributed Trust Management Reputation-based TM Rule-based TM

04/09/2009Minor project course19 Reputation-based TM (concrete) community of cooks (200 people) to establish trust: you ask your friends  and friends of friends ... some recommendations are better than others you check the record (if any) after success trust increases

04/09/2009Minor project course20 Reputation-based TM (virtual) eBay (hundreds of millions of users)

04/09/2009Minor project course21 Reputation-based TM (virtual) Buyers and sellers rate each other after a transaction Positive (r(i,j) = 1) Neutral (r(i,j) = 0) Negative (r(i,j) = -1)

04/09/2009Minor project course22 Key features open system (different security domains) trust is a measure & changes in time essential risk component recommendation based (NOT identity-based) peers are not continuously available Algorithms (e.g., EigenTrust)

04/09/2009Minor project course23 Outline Introduction to Access Control Discretionary and Mandatory Access Control Role-Based Access Control Distributed Trust Management Reputation-based TM Rule-based TM

04/09/2009Minor project course24 Rule-based TM (concrete) Bart is entitled to a discount If he is a student of the local university

04/09/2009Minor project course25 Rule-based TM (virtual) When is Bart now entitled to a discount?

04/09/2009Minor project course26 Bart is entitled to a discount… If he is a student of any accredited University. But perhaps also… If he is an employee of any governmental organization If he is a member of the library club If he is a veteran …. Too many to mention Which problems does this raise? Scalability Knowing where and what to search

04/09/2009Minor project course27 Reputation vs. Rules open system (different security domains) trust is a measure & changes in time risk-based no delegation recommendation based (NOT identity-based) peers are not continuously available scalability open system (different security domains) trust is boolean & less time- dependent no risk delegation rule (credential) based (NOT identity-based) peers are not continuously available scalability

04/09/2009Minor project course28 Credentials A credential is a statement Signed by the issuer about a subject Containing info about the subject Requirements Unforgeable (!) Verifiable (that it belongs to the subject asking for the service) Signed (e.g. X509)

04/09/2009Minor project course29 Credential Chains Bart TU/e Accreditation Bureau Shop Is student of Is accredited by Is accepted by We have a chain of credentials The subject of one is the issuer of the other one

04/09/2009Minor project course30 Languages for TM A good language for TM must be able to express: Decentralized attributes Delegation of attribute authority Inference of attributes Attribute fields (e.g., age) Attribute-based delegation of authority

04/09/2009Minor project course31 Decentralized Attributes An entity asserts that another entity has a certain attribute e.g., student(TU/e,Alice) The TU/e asserts that Alice is a student Issuer: TU/e Subject: Alice Where is it stored?

04/09/2009Minor project course32 Delegation of Attribute Authority An entity delegates (i.e. trusts) the authority over an attribute to another entity e.g., student(DSA,X)  student(TU/e,X) The “Dutch Students Association” considers as students all the students of the TU/e Operationally: anyone showing a TU/e student credential can get a student credential from the DSA Issuers: DSA, TU/e Subject: X

04/09/2009Minor project course33 Inference of Attributes An entity uses one attribute to make inferences about another attribute e.g., employee(TU/e,X)  professor(TU/e,X) The TU/e asserts that every TU/e professor is also a TU/e employee

04/09/2009Minor project course34 Attribute Fields Credentials may carry field values e.g. student(DSA,Alice,university=TU/e) Field values can be used to infer additional attributes and for conditional delegation e.g. ccard(VISA,X)  client(ABN,X,credit=Y) AND Y > 2000 VISA releases credit cards only to ABN clients with more than 2000€ in their account

04/09/2009Minor project course35 Attribute-based Delegation of Authority An entity may delegate the authority to another entity depending on its attributes e.g. ccard(VISA,X)  client(Y,X) AND certified(EB,Y) VISA releases a credit card only to clients of banks which are certified by the “European Bank” By doing so, VISA does not need to explicitly mention all the banks which are trusted VISA trusts EB’s opinion about banks

04/09/2009Minor project course36 Credential Storage Every credential can be stored by its issuer, its subject, or a third party When we try to build a credential chain, we must be able to retrieve the appropriate credentials Credential chain discovery algorithms suggest storage schemas according to which credentials are retrieved RT: backward and forward search algorithm TuLiP POLIPO

04/09/2009Minor project course37 In the next lecture… The POLIPO framework a rule-based TM language a reputation system an algorithm for credential chain discovery

04/09/2009Minor project course38 Thank you for your attention! Questions?