© Ravi Sandhu The Secure Information Sharing Problem and Solution Approaches Ravi Sandhu Executive Director and Endowed Chair Institute

© Ravi Sandhuwww.profsandhu.com

The Secure Information Sharing Problem and Solution Approaches

Ravi SandhuExecutive Director and Endowed Chair

Institute for Cyber SecurityUniversity of Texas at San Antonio

www.profsandhu.com

http://www.profsandhu.com/


2 © Ravi Sandhuwww.profsandhu.com

Three Themes Secure Information

Sharing (IS)“Share but Protect”

“Mother of all Security Problems”

TrustedComputing (TC)

Policy-Enforcement-Implementation Layers (PEI)

&Usage Control Models (UCON)

Work in Progress



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

What is Trusted Computing (TC)?

Massive paradigm shift

Prevent information leakage by binding information to Trusted Viewers on the client

How best to leveragethis technology?



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



What is Information Sharing?Strength of Enforcement

Content type and value Weak Medium Strong

Sensitive and proprietary Password-protected documents Software-based client controls for documents

Hardware based trusted viewers, displays and inputs

Revenue driven IEEE, 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 revenue Analyst 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.


Functionality Strength of enforcement

Simple Complex Weak/Medium Strong

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 controls Control 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.

Revocation Simple 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.

Audit Audit support for basic dissemination operations.

Additional support for the audit of instance usage.

Offline audit analysis. Real-time audit analysis and alerts.

Payment Simple 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 knowledgethe information sharing spaceis too complex to characterizein a comprehensive manner

Look for sweet spots thatare of practical interest

and where progress (andkiller products) can be made

Roshan Thomas and Ravi Sandhu, “Towards a Multi-Dimensional Characterization of Dissemination Control.” POLICY04.


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


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-rootedTrusted Computing assurance ofclient-side controls is very weak


PEI Models Framework

Security and system goals(requirements/objectives)

Target platform, e.g., TrustedComputing technology

Enforcement models

Policy models

Implementation models

Horizontalview

Looks atIndividual

layer

VerticalViewLooksAcrossLayers


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

Required to support super-distribution

Supports fine-grained controls and policy flexibility

Limits instant and pre-emptive revocation





Enforcement models

Policy models


Horizontalview

Looks atIndividual

layer



Various states of a member in a group

Initial state:Never been a

member

State I

Currently a member

State II

Past member

State III

enroll dis-enroll

enroll


Access policies for State I


member

State I

Currently a member

State II

Past member

State III

enroll dis-enroll

1. Straight-forward. User has no access to any group documents.

enroll


Access policies for State II


member

State I

Currently a member

State II

Past member

State III

enroll dis-enroll

1. Access to current documents only (or)2. Access to current documents and past

documents3. Access can be further restricted with rate

and/or usage limits4. Access can be further restricted on basis

of individual user credentialsenroll


Access policies for State III


member

State I

Currently a member

State II

Past member

State III

enroll dis-enroll

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 restrictionsenroll


Access policies for State II.re-enroll


member

State I

Currently a member

State II

Past member

State III

enroll dis-enroll

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 cyclesenroll


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. A master system could be ViiV enabled which subscribes to various kinds of channels from its content providers

b. Many devices can in-turn subscribe to this master device and receive content and thus form a group

c. 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.


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.


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.


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.


Various states of an object (document) in a group


group doc

State I

Currently a group doc

State II

Past group doc

State III

add remove

add


Access policies for State I


group doc

State I


State II

Past group doc

State III

add remove

1. Straight-forward. No access to group members.

add


Access policies for State II


group doc

State I


State II

Past group doc

State III

add remove

1. Access allowed only to current group members

2. Access allowed to current and past group members

add


Access policies for State III


group doc

State I


State II

Past group doc

State III

add remove

1. No one can access2. Any one can access3. Past members can

access

add


Access policies for State II.re-add


group doc

State I


State II

Past group doc

State III

add remove

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 add


Policy Models

Idealized policy:• Instant revocation• Pre-emptive revocation

Enforcement models will specify degree of approximation (among other details)


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-addedThe PEI models have specific points where such policies are enforced and

remain robust to changes in policy details


Usage Control: The UCON Model

Rights(R)

Authorizations

(A)

Subjects(S)

Objects(O)

Subject Attributes (SA) Object Attributes (OA)

Obligations(B)

Conditions(C)

UsageDecisions

before-usage ongoing-Usage after-usage

Continuity ofDecisions

pre-decision ongoing-decision

pre-update ongoing-update post-update

Mutability ofAttributes

• unified model integrating• authorization• obligation• conditions

• and incorporating• continuity of decisions• mutability of attributes


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


Policy model: member enroll/dis-enroll


member

State I

Currently a member

State II

Past member

State III

enroll dis-enroll

memberTS-joinTS-leave

nullnullnull

Truetime of joinnullenroll

Falsetime of jointime of leavedis-enroll

enroll

enroll, dis-enroll: authorized to Group-Admins

UCON elements:Pre-Authorization, attribute predicates, attribute mutability

enroll


Policy model: document add/remove


group doc

State I


State II

Past group doc

State III

add remove

D-memberD-TS-joinD-TS-leave

nullnullnull

Truetime of joinnulladd

Falsetime of jointime of leaveremove

add, remove : authorized to Group-Admins

add

UCON elements:Pre-Authorization, attribute predicates, attribute mutability

add


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 mutabilityOngoing-authorization





Enforcement models

Policy models


Horizontalview

Looks atIndividual

layer



Enforcement Models

Design Principle• Do not inject new policy• Focus on trade-offs for instant and pre-emptive revocation versus off-line

accessFaithful 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


Enforcement Architecture

3

1

2 4 5

Group-Admin MemberJoining Member

Control Center (CC)

7

Faithful Model: steps 3 and 4 are coupledApproximate 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 member’s computer


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


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)


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


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


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





Enforcement models

Policy models


Horizontalview

Looks atIndividual

layer


• Out of scope for this talk


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


Q&A Secure Information

Sharing (IS)“Share but Protect”

“Mother of all Security Problems”

TrustedComputing (TC)

Policy-Enforcement-Implementation Layers (PEI)

&Usage Control Models (UCON)

Work in Progress