The Secure Information Sharing Problem and Solution Approaches

1. The Secure Information Sharing Problem and Solution Approaches Ravi Sandhu Executive Director and Endowed Chair Institute for Cyber Security University of Texas at San Antonio www.profsandhu.com

2. Three Themes Secure Information Sharing (IS) “Share but Protect” “Mother of all Security Problems” Work in Progress Policy-Enforcement- Implementation Layers (PEI) & Usage Control Models (UCON) Trusted Computing (TC)

3. What is Trusted Computing (TC)? • Basic premise • Software alone cannot provide an adequate foundation for trust • Old style Trusted Computing (1970 – 1990’s) • Multics system • Capability-based computers • Intel 432 vis a vis Intel 8086 • Trust with security kernel based on military-style security labels • Orange Book: eliminate trust from applications • What’s new (2000’s) • Hardware and cryptography-based root of trust • Trust within a platform • Trust across platforms • Rely on trust in applications • No Trojan Horses or • Mitigate Trojan Horses and bugs by legal and reputational recourse How best to leverage this technology? Massive paradigm shift Prevent information leakage by binding information to Trusted Viewers on the client

4. What is Information Sharing? • The mother of all security problems • Share but protect • Requires controls on the client • Server-side controls do not scale to high assurance • Bigger than (but includes) • Retail DRM (Digital Rights Management) • Enterprise DRM

5. What is Information Sharing? Roshan Thomas and Ravi Sandhu, “Towards a Multi-Dimensional Characterization of Dissemination Control.” POLICY04.

6. With current state of knowledge the information sharing space is too complex to characterize in a comprehensive manner Look for sweet spots that are of practical interest and where progress (and killer products) can be made Roshan Thomas and Ravi Sandhu, “Towards a Multi-Dimensional Characterization of Dissemination Control.” POLICY04.

7. Classic Approaches to Information Sharing • Discretionary Access Control (DAC), Lampson 1971 • Fundamentally broken • 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 • Thorny issues of covert channels, inference, aggregation remain but can be confronted • Does not scale to fine-grained sharing • Super-exponential explosion of security labels is impractical • Fallback to DAC for fine-grained control (as per the Orange Book) is pointless • Originator Control (ORCON), Graubart 1989 • Propagated access control lists: let copying happen but propagate ACLs to copies (or extracts) Not very successful

8. Modern Approach to Information Sharing • Prevent leakage by binding information to Trusted Viewers on the client • Use a mix of cryptographic and access control techniques • Cryptography and Trusted Computing primitives enable encapsulation of content in a Trusted Viewer • Trusted Viewer cannot see plaintext unless it has the correct keys • Access control enables fine-grained control and flexible policy enforcement by the Trusted Viewer • Trusted Viewer will not display plaintext (even though it can) unless policy requirements are met • Enables policy flexibility and policy-mechanism separation Without use of hardware-rooted Trusted Computing assurance of client-side controls is very weak

9. PEI Models Framework

10. Scoping Information Sharing Problem:Objective Layer • Scoping the Problem • Read-only (versus read-write) • Document-level controls (versus query-level control) • Superdistribution (encrypt once, access wherever authorized) • Support for off-line access without advance set-up (with usage limits) • Scoping the Solution • Two-phase enforcement • Enroll TPM (Trusted Platform Module) and LaGrande equipped client computer into a Group • Within the Group impose additional policy-based controls Limits instant and pre-emptive revocation Required to support super-distribution Supports fine-grained controls and policy flexibility

11. PEI Models Framework

12. Various states of a member in a group enroll Initial state: Never been a member State I Currently a member State II Past member State III enroll dis-enroll

13. Access policies for State I • Straight-forward. User has no access to any group documents. enroll Initial state: Never been a member State I Currently a member State II Past member State III enroll dis-enroll

14. Access policies for State II • Access to current documents only (or) • Access to current documents and past documents • Access can be further restricted with rate and/or usage limits • Access can be further restricted on basis of individual user credentials enroll Initial state: Never been a member State I Currently a member State II Past member State III enroll dis-enroll

15. Access policies for State III • Past member loses access to all documents (or) • can access any document created during his membership (or) • can access documents he accessed during membership (or) • can access all documents created before he left the group (this includes the ones created before his join time) • all subject to possible additional rate, usage and user credential restrictions enroll Initial state: Never been a member State I Currently a member State II Past member State III enroll dis-enroll

16. Access policies for State II.re-enroll • No rejoin of past members is allowed, rejoin with new ID (or) • Past members rejoin the group just like any other user who has never been a member • The same access policies defined during his prior membership should again be enforced (or) • access policies could vary between membership cycles enroll Initial state: Never been a member State I Currently a member State II Past member State III enroll dis-enroll

17. Use-case 1 • Access policies: II.1, III.1, II.re-enroll.1 • Intel’s ViiV: A typical scenario in libraries, book-stores, cafes, etc. • A master system could be ViiV enabled which subscribes to various kinds of channels from its content providers • Many devices can in-turn subscribe to this master device and receive content and thus form a group • When a device leaves the group, it loses access to all the downloaded content. “Leaving the group” could be determined by various mechanisms depending on context and available technology (location, network connectivity, etc.). • Many universities and corporations allow access to their content as long as one is within their network. Once the user leaves the network, the user loses access to the content.

18. Use-case 2 • Access policies: II.1, III.2, II.re-enroll.1: • Project out-sourcing: • A financial organization could recruit a software-consulting firm to provide software solutions. This forms a temporary group. • The incoming members (from the software firm) cannot access any past documents. These could be design documents that were created in collaboration with a different external organization. • When they finish the project and leave the group, they can continue to have access to the documents exchanged during their membership for future reference and to add to their profile. This is dependant on financial institution’s policy.

19. Use-case 3 • Access policies: II.2, III.1, II.re-enroll.1: • An employee in a company can access all the current documents. When he employee quits, he should lose access to all documents. • DoD projects / contracts have a multi tiered structure. A member of a contracting company may be authorized to access certain set of documents only for the duration of the project – once the project is over, the contractor’s right to use the document is automatically voided. • In a supply chain situation, there are lots of partners and suppliers who will send quotes for a given proposal. They need to have access to the proposal and related content. But once the quote/response is submitted, their membership context for that particular or group of proposals ceases and they shouldn’t have access to any of the older content that they had access to.

20. Use-case 4 • Access policies: II.2, III.2, II.re-enroll.1: • Collaborative product development: • In the case of several automobile models, there are product twins – models from the same company that resemble each other, except for the division's brand name and price tag. • In such instances, there could be either a loose collaboration (e.g. shared design team, parts ordering/manufacturing but different factories) or a tight collaboration (e.g. joint manufacturing of two different models). • In either case, the members from different parties join hands and share documents actively. • They will need access to both old documents and current documents. Even after the collaboration period, they will need access to the old documents for further refinement and production.

21. Various states of an object (document) in a group add Initial state: Never been a group doc State I Currently a group doc State II Past group doc State III add remove

22. Access policies for State I • Straight-forward. No access to group members. add Initial state: Never been a group doc State I Currently a group doc State II Past group doc State III add remove

23. Access policies for State II • Access allowed only to current group members • Access allowed to current and past group members add Initial state: Never been a group doc State I Currently a group doc State II Past group doc State III add remove

24. Access policies for State III • No one can access • Any one can access • Past members can access add Initial state: Never been a group doc State I Currently a group doc State II Past group doc State III add remove

25. Access policies for State II.re-add • Cannot be re-added. • When a document is re-added, it will be treated as a new document that is added into the group. • Only current members can access. • Past members and current members can access add Initial state: Never been a group doc State I Currently a group doc State II Past group doc State III add remove

26. Policy Models • Idealized policy: • Instant revocation • Pre-emptive revocation • Enforcement models will specify degree of approximation (among other details)

27. Policy Models • Group membership control • Group-admins enroll and dis-enroll members • Group-admins add/remove documents. • For concreteness we assume specific group-level policies • Members cannot access documents created prior to joining • Past-members can access documents created during (most recent) membership • Past documents cannot be accessed by anybody • Documents cannot be re-added The PEI models have specific points where such policies are enforced and remain robust to changes in policy details

28. Usage Control: The UCON Model • unified model integrating • authorization • obligation • conditions • and incorporating • continuity of decisions • mutability of attributes

29. UCON Policy Model • Operations that we need to model: • Document read by a member. • Adding/removing a member to/from the group • Adding/removing a document to/from the group • Member attributes • Member: boolean • TS-join: join time • TS-leave: leave time • Document attributes • D-Member: boolean • D-TS-join: join time • D-TS-leave: leave time

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

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

32. 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

33. PEI Models Framework

34. 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

35. Enforcement Architecture Control Center (CC) • Two sets of attributes • Authoritative: as known to the CC • Local: as known on a member’s computer 4 2 3 5 7 1 • 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) Joining Member Group-Admin Member 6 D-Member Faithful Model: steps 3 and 4 are coupled Approximate Model: steps 3 and 4 are de-coupled

36. UCON Enforcement Models • Member attributes • Member-a, Member-l: boolean • TS-join-a, TS-join-l: join time • TS-leave-a, TS-leave-l: leave time • Document attributes • D-Member-a, D-Member-l: boolean • D-TS-join-a, D-TS-join-l: join time • D-TS-leave-a, D-TS-leave-l: leave time • Additional Member attributes for Approximate model: • refresh_count: decremented on every access • refresh_count_reset: refresh_count is reset to this value when it hits 0

37. 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)

38. 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

39. 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

40. 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

41. PEI Models Framework • Out of scope for this talk

42. Conclusion • Information sharing is an important security problem and a potential growth area • Trusted computing is a good fit for solving some sweet spots in this space • The PEI models framework is useful in closing the policy-implementation gap • UCON is a useful framework for stating policy and enforcement models

43. Q&A Secure Information Sharing (IS) “Share but Protect” “Mother of all Security Problems” Work in Progress Policy-Enforcement- Implementation Layers (PEI) & Usage Control Models (UCON) Trusted Computing (TC)