1 PEI Models towards Scalable, Usable and High-assurance Information Sharing Ram Krishnan Laboratory for Information Security Technology George Mason University Kumar Ranganathan Intel Systems Research Center Bangalore, India Ravi Sandhu Institute for Cyber-Security Research Univ of Texas at San Antonio

2 Presentation Outline Problem Description & Motivation Background –Trusted Computing –Information Sharing PEI Models for SIS Future Work Q&A

3 Problem Description & Motivation Secure Information Sharing (SIS) –Share but protect Distribute information and still retain control –Long-standing and unsolved problem Current approaches to SIS: –Discretionary Access Control (DAC), Lampson 1971 Fundamentally limited Controls access to the original but not to copies (or extracts) –Mandatory Access Control (MAC), Bell-LaPadula 1971 Solves the problem for coarse-grained sharing Does not scale to fine-grained sharing –Explosion of security labels –Originator Control (ORCON), Graubart 1989 Let copying happen but propagate ACLs to copies (or extracts)

4 …continued SIS problem further amplified by the client-server model –No control once information leaves server –Current approaches are software-based Inherently weak Fundamental question: –How can I trust that policies will be enforced on clients in a trust- worthy manner? Trusted Computing (TC) Technology features root of trust at hardware level –Potential to provide strong controls on client –Potential to solve SIS problem We need a family of models to guide TC-based solutions

5 Background

6 Trusted Computing An industry standard/alliance –Proposed by Trusted Computing Group Basic premise –Software alone cannot provide an adequate foundation for trust TCG proposes root of trust at the hardware level using a Trusted Platform Module or TPM

7 TPM: 3 novel features Trusted storage for keys –Encrypt user keys with a chain of keys –Root key is stored in TPM & never exposed Trusted Capabilities –Operations exposed by the TPM –Guaranteed to be trust-worthy Platform Configuration Registers (PCR) –Hardware registers used to store integrity of software (e.g. boot-chain)

8 TPM: An example functionality Seal –Trusted capability –Encrypts and binds data to a PCR value –Data can be unsealed iff PCR value at unseal time matches with PCR value in sealed blob Seal can be used to restrict data access –E.g. A program can access sensitive information only if the platform is in trustworthy state

9 What is Information Sharing? Share but protect –Distribute information and still retain control Requires strong controls on client –Server controls information release only Purpose is larger than retail DRM...

10 What is Information Sharing? Strength of Enforcement Content type and valueWeakMediumStrong Sensitive and proprietaryPassword-protected documentsSoftware-based client controls for documents Hardware based trusted viewers, displays and inputs Revenue drivenIEEE, ACM digital libraries protected by server access controls DRM-enabled media players such as for digital music and eBooks Dongle-based copy protection, hardware based trusted viewers, displays and inputs Sensitive and revenueAnalyst and business reports protected by server access controls Software-based client controls for documents Hardware based trusted viewers, displays and inputs Roshan Thomas and Ravi Sandhu, Towards a Multi-Dimensional Characterization of Dissemination Control. POLICY04.

11 FunctionalityStrength of enforcement SimpleComplexWeak/MediumStrong Legally enforceable versus system enforced rights. Reliance on legal enforcement; Limited system enforced controls. Strong system- enforceable rights, revocable rights. Dissemination chains and flexibility. Limited to one-step disseminations. Flexible, multi-step, and multi-point.Mostly legal enforcement;System enforceable controls. Object types supported. Simple, read-only and single- version objects. Support for complex, multi-version objects. Support for object sensitivity/confidentiality. Reliance on legally enforceable rights. System supported and enforceable rights and sanitization on multiple versions. Persistence and modifiability of rights and licenses. Immutable, persistent and viral on all disseminated copies. Not viral and modifiable by recipient.Reliance on legally enforceable rights. System enforceable. Online versus offline access and persistent client-side copies No offline access and no client-side copies. Allows offline access to client-side copies. Few unprotected copies are tolerated. No unprotected copies are tolerated. Usage controlsControl of basic dissemination. Flexible, rule-based usage controls on instances. Some usage abuse allowed. No potential for usage abuse. Preservation of attribution. Recipient has legal obligation to give attribution to disseminator. System-enabled preservation and trace- back of the attribution chain back to original disseminator. Attribution can only be legally enforced. Attribution is system enforced. RevocationSimple explicit revocations.Complex policy-based revocation.No timeliness guarantees.Guaranteed to take immediate effect. Support for derived and value-added objects. Not supported.Supported.Reliance on legally enforceable rights. System enforceable rights for derived and valued-added objects. Integrity protection for disseminated objects. Out of band or non-crypto based validation. Cryptographic schemes for integrity validation. Off-line validation.High-assurance cryptographic validation. AuditAudit support for basic dissemination operations. Additional support for the audit of instance usage. Offline audit analysis.Real-time audit analysis and alerts. PaymentSimple payment schemes (if any). Multiple pricing models and payment schemes including resale. Tolerance of some revenue loss. No revenue loss; Objective is to maximize revenue. With current state of knowledge the information sharing space is too complex to characterize in a comprehensive manner Look for areas that are of practical interest and where progress can be made Roshan Thomas and Ravi Sandhu, Towards a Multi-Dimensional Characterization of Dissemination Control. POLICY04.

12 PEI Models for SDS

13 SDS Objectives Super-distribution (encrypt once, access wherever authorized) –Requires a notion of a group A subject is authorized to access a document if he is a group member Problem scope: group-based SDS Offline access Document-level access control Read-only document access Security and system goals (requirements/objectives) Target platform, e.g., Trusted Computing Technology Enforcement models Policy models Implementation models

14 SDS Policy Model Characterize policies applicable to a group-based SDS problem domain Security and system goals (requirements/objectives) Target platform, e.g., Trusted Computing Technology Enforcement models Policy models Implementation models

15 Various states of a group member Initial state: Never been a member State I Currently a member State II Past member State III enrolldis- enroll enroll 1. Straight-forward. User has no access to any group documents. 1. Access to current documents only (or) 2. Access to current documents and past documents 3. Access can be further restricted with rate and/or usage limits 4. Access can be further restricted on basis of individual user credentials 1. Past member loses access to all documents (or) 2. can access any document created during his membership (or) 3. can access documents he accessed during membership (or) 4. can access all documents created before he left the group (this includes the ones created before his join time) 5. all subject to possible additional rate, usage and user credential restrictions 1. No rejoin of past members is allowed, rejoin with new ID (or) 2. Past members rejoin the group just like any other user who has never been a member 3. The same access policies defined during his prior membership should again be enforced (or) 4. access policies could vary between membership cycles

16 Various states of a group document Initial state: Never been a group doc State I Currently a group doc State II Past group doc State III addremove add 1. Straight-forward. No access to group members. 1. Access allowed only to current group members 2. Access allowed to current and past group members 1. No one can access 2. Any one can access 3. Past members can access 1. Cannot be re-added. 2.When a document is re-added, it will be treated as a new document that is added into the group. 3.Only current members can access. 4.Past members and current members can access

17 Policy model: member enroll/dis-enroll Initial state: Never been a member State I Currently a member State II Past member State III enrolldis- enroll member TS-join TS-leave null True time of join null enroll False time of join time of leave dis-enroll enroll enroll, dis-enroll: authorized to Group-Admins UCON elements: Pre-Authorization, attribute predicates, attribute mutability enroll

18 Policy model: document add/remove Initial state: Never been a group doc State I Currently a group doc State II Past group doc State III add remove D-member D-TS-join D-TS-leave null True time of join null add False time of join time of leave remove add, remove : authorized to Group-Admins add UCON elements: Pre-Authorization, attribute predicates, attribute mutability add

19 Enforcement Models Develop enforcement models for SDS Security and system goals (requirements/objectives) Target platform, e.g., Trusted Computing Technology Enforcement models Policy models Implementation models

20 SDS Enforcement Model Group-AdminMember Joining Member Control Center (CC) 7 Faithful Model: steps 3 and 4 are coupled Approximate Model: steps 3 and 4 are de-coupled D-Member 6 Member enroll and dis-enroll (steps 1-2, 5) Document add and remove (step 6, 7) Read policy enforcement (step 3) Attribute update (step 4) Two sets of attributes Authoritative: as known to the CC Local: as known on a members computer

21 Implementation Models Develop implementation models for SDS Security and system goals (requirements/objectives) Target platform, e.g., Trusted Computing Technology Enforcement models Policy models Implementation models

22 Implementation Model Build a Trusted Reference Monitor (TRM) –The reference monitor on the group members that enforces group policies in a trust-worthy manner Identify the Trusted Computing Base (TCB) –A minimal collection of entities that is absolutely essential to be in integral state in order to preserve security of the entire system Objective –Build a TCB in order to enforce document read on group members using a TRM Two Key requirements –Only TRM can access the group key and read/write subject and object attributes –TRM is provided with isolated environment to safely use the group/document keys

23 Implementation Model (continued) Use TC mechanisms to bind group key + attributes to TRM

24 Future Work Formal analysis of SIS policy models –SDS: object level –SCS: attribute level Document/object Read and Write SIS across multiple groups –Information flow issues Document/object-level querying –Obtain sections of document/object Coffee ShopBook Store Credit Alice SCS in M-commerce Scenario

25 Q&A Thanks! Information Sharing Policy, Enforcement, Implementation (PEI) layers Trusted Computing (TC) Usage CONtrol model (UCON)

26 Backup

27 Policy model: document read (S,O,read) Pre-authorization check –member(S) null AND D-member(O) null AND TS-join(S) null AND D-TS-join(O) null AND TS-leave(S) = null AND TS-join(S) D-TS-join(O) OR TS-leave(S) null AND TS-join(S) D-TS-join(O) TS-leave(O) Ongoing-authorization check: terminate if –D-TS-leave(O) null Details depend on details of group-level policy UCON elements: Pre-Authorization, attribute predicates, attribute mutability Ongoing-authorization

28 Enforcement Models Design Principle –Do not inject new policy –Focus on trade-offs for instant and pre-emptive revocation versus off- line access Faithful Enforcement w/o Off-line Access (Faithful Model): –We need continuous online touch (at start of every access and during access) –Continuous on-line touch can only be approximated Usage-limited Off-line Access (Approximate Model): –We need online touch periodically after some duration (at start of every access and during access) Duration between online touches can be based on time, but time is not practical for TPM-based TC Duration between online touches can be based on usage count, which is practical for TPM-based TC

29 Faithful model highlights enroll a member: two steps –Step 1: Group-admin issues enrollment token to Joining Member –Step 2: Joining Member presents token to CC and receives group membership credential Group key (symmetric key) Local attribute values dis-enroll a member –Updates authoritative attributes at CC –Takes effect on local attributes at next update add a document –Updates authoritative attributes at CC remove a document –Updates authoritative attributes at CC –Propagated to clients as DRLs (Document Revocation List)

30 Faithful model highlights: (S,O,read) Pre-Obligation –Local attributes of S and O are updated based on authoritative values from CC –Local DRL updated from authoritative DRL at CC Pre-Condition –Requires connectivity to enable updates Pre-Authorization –Based on just updated local attributes of S and O and DRL Ongoing-Obligation –Local attributes of S and O continuously updated based on authoritative values from CC –Local DRL continuously updated from authoritative DRL at CC Ongoing-Condition –Requires connectivity to enable updates Ongoing-Authorization –Based on continuously updated local attributes of S and O and DRL UCON elements: Requires full power of UCON

31 Approximate model highlights enroll a member: two steps –Step 1: Group-admin issues enrollment token to Joining Member –Step 2: Joining Member presents token to CC and receives group membership credential Group key (symmetric key) Local attribute values dis-enroll a member –Updates authoritative attributes at CC –Takes effect on local attributes at next update add a document –Updates authoritative attributes at CC remove a document –Updates authoritative attributes at CC –Propagated to clients as DRLs (Document Revocation List) Different from Faithful model

32 Approximate model highlights: (S,O,read) Pre-Obligation –Local attributes of S and O are periodically updated based on authoritative values from CC Pre-Condition –Requires connectivity to enable updates when required Pre-Authorization –Based on just updated local attributes of S and O Ongoing-Obligation –Local attributes of S and O are continuously periodically updated based on authoritative values from CC Ongoing-Condition –Requires connectivity to enable updates when required Ongoing-Authorization –Based on continuously periodically updated local attributes of S and O UCON elements: Requires full power of UCON

33 Contributions & Conclusions SIS is a broad and complex problem –PEI framework, UCON model and TC are highly useful for approaching the SIS problem space First steps towards developing a family of models for SIS problem domain –Classify SIS into two distinct levels: Object-level SIS Attribute-level SIS –Analyze object-level and attribute-level SIS Demonstrate how TC can be used to address this long- standing problem Possibly extend the UCON model Leave with more open questions!