Trusted Computing and Digital Rights Management in aDe-perimeterised Environmentseminar to Dennis Soongs groupat Lenovo R&D, Beijing
Prof. Clark Thomborson
3rd April 2007
OutlineAn operational definition of trust.Requirements analysis of e-government and corporate DRM (ECM) at three levels: static, dynamic, governance.Suggested design improvementsDRM: Emphasise integrity and availability, not confidentialityTC: More support for auditRelationship Management: support for hierarchical, bridging, and peering trust with other systems and individualsSteps toward uniform purchase requirements with emphasis on interoperability and appropriate security.In progress at the Jericho Forum.Eventually: develop an appropriate audit standard for DRM, TC, and relationship management.
Trust and PrivilegeWe must develop operational definitions for these terms, if we wish to develop trustworthy computer systems.
Technical and non-technical definitions of Trust In security engineering, placing trust in a system is a last resort.Its better to rely on an assurance (e.g. a proof, or a recourse mechanism), than on a trusting belief that shell be right.In non-technical circles, trust is a good thing: more trust is generally considered to be better.Trustworthiness (an assurance) implies that trust (a risk-aware basis for a decision) is well-placed.A completely trustworthy system (in hindsight) is one that has never violated the trust placed in it by its users.Just because some users trust a system, we cannot conclude that the system is trustworthy.A rational and well-informed person can estimate the trustworthiness of a system.Irrational or poorly-informed users will make poor decisions about whether or not, and under what circumstances, to trust a system.
Privilege in a HierarchyInformation flows upwards, toward the most powerful actor (at the root).Commands and trust flow downwards.The King is the most privileged.The peons are the most trusted.King, President, Chief Justice, Pope, or Peons, illegal immigrants, felons, excommunicants, or Information flowing up is privileged.Information flowing down is trusted.Orange book TCSEC, e.g. LOCKix.
Trustworthiness in a HierarchyInformation flows upwards, toward the most powerful actor.Commands and trust flow downwards.Peons must be trusted with some information!If the peons are not trustworthy, then the system is not secure. King, President, Chief Justice, Pope, or Peons, illegal immigrants, felons, excommunicants, or If the King does not show good leadership (by issuing appropriate commands), then the system will not work well. Noblesse oblige!
Email in a HierarchyInformation flows upwards, toward the leading actor. Actors can send email to their superiors.Non-upwards email traffic is trusted:not allowed by default;should be filtered, audited, King, President, Chief Justice, Pope, or Peons, illegal immigrants, felons, excommunicants, or Email up: privileged (allowed by default)Email down: trusted (disallowed by default, risk to confidentiality)Email across: privileged & trusted routing
Email across HierarchiesQ: How should we handle email between hierarchies?Company XAgency YAnswers:MergeSubsumeBridgeNot often desirable or even feasible.Cryptography doesnt protect X from Y, because the CEO/King of the merged company has the right to know all keys.Can an appropriate King(X+Y) be found?
Email across HierarchiesQ: How can we manage email between hierarchies?Agency XCompany YAnswers:MergeSubsumeBridge
Email across HierarchiesQ: How can we manage email between hierarchies?Company XAgency YAnswers:MergeSubsumeBridge!Bridging connection: trusted in both directions.
Bridging TrustWe use bridges every time we send personal email from our work computer.We build a bridge by constructing a bridging persona.Even Kings can form bridges.However Kings are most likely to use an actual person, e.g. their personal secretary, rather than a bridging persona.Agency XHotmailBridging connection: bidirectional trusted.Used for all communication among an actors personae.C should encrypt all hotmail to avoid revelations.C, acting as a governmental agentC, acting as a hotmail client
Personae, Actors, and AgentsI use actor to refer toan agent (a human, or a computer program),pursuing a goal (risk vs. reward),subject to some constraints (social, technical, ethical, )In Freudian terms: ego, id, superego.Actors can act on behalf of another actor: agency.In this part of the talk, we are considering agency relationships in a hierarchy. Company XHotmailWhen an agent takes on a secondary goal, or accepts a different set of constraints, they create an actor with a new persona. C, acting as an employeeC, acting as a hotmail client
Bridging Trust: B2B e-commerceUse case: employee C of X purchasing supplies through employee V of Y.Employee C creates a hotmail account for a purchasing persona.Purchaser C doesnt know any irrelevant information.Company XCompany YMost workflow systems have rigid personae definitions (= role assignments).Current operating systems offer very little support for bridges. Important future work!C, acting as an employeeC, acting as a purchaserEmployee V
Why cant we trust our leaders? Commands and trust flow upwards (by majority vote, or by consensus). Information flows downwards by default (privileged).Upward information flows are trusted (filtered, audited, etc.)In a peerage, the leading actors are trusted, have minimal privilege, dont know very much, and can safely act on anything they know.Our leaders are but trusted servantsPeersBy contrast, the King of a hierarchy has an absolute right (root privilege) to know everything, is not trusted, and cannot act safely.
Turn the picture upside down! Information flows upwards by default (privileged).Commands and trust flow downwards. Downward information flows are trusted (filtered, audited, etc.)A peerage can be modeled by Bell-La Padula, because there is a partial order on the actors privileges.Equality of privilege is the default in a peerage, whereas inequality of privilege is the default in a hierarchy.Facilitator, Moderator, Democratic Leader, Peers, Group members, Citizens of an ideal democracy,
Peer trust vs. Hierarchical trustTrusting decisions in a peerage are made by peers, according to some fixed decision rule.There is no single root of peer trust.There are many possible decision rules, but simple majority and consensus are the most common.Weighted sums in a reputation scheme (e.g. eBay for goods, Poblano for documents) are a calculus of peer trust -- but we must all agree to abide by the scheme.First come, first serve (e.g. Wiki) can be an appropriate decision rule, if the cost per serving is sufficiently low.Trusting decisions in a hierarchy are made by its most powerful members.Ultimately, all hierarchical trust is rooted in the King.
Legitimation and enforcementHierarchies have difficulty with legitimation.Why should I swear fealty (give ultimate privilege) to this would-be King?Peerages have difficulty with enforcement.How could the least privileged actor possibly be an effective facilitator?This isnt Political Science 101!I will not try to model a government. Its hard enough to build a model that will help us develop a better computer system!I have tried to convince you that hierarchical trust is quite different to peer trust, that bridging trust is also distinct, and that all three forms are important in our world.My thesis: Because our applications software will help us handle all three forms of trust, therefore our trusted operating systems should support all three forms.
Requirements for Relationship ManagementOrange-book security is hierarchical.This is a perfect match to a military or secret-service agency.This is a poor match to e-government and corporate applications.A general-purpose TC must support bridging and peering relationships.Rights-management languages must support bridges and peerages, as well as hierarchies.We cannot design an attractive, general purpose DRM system until we have designed the infrastructure properly!
VapourwareClosed-source methodology is appropriate for designing hierarchical systems.These systems have trouble with legitimation.Why should a user trust that the system designers (and administrators) wont abuse their privilege? Open-source methodology is appropriate for designing peerage systems.These systems have trouble with enforcement.Why should anyone trust a user not to abuse their privilege?Real-world peerages can legitimise hierarchies, and hierarchies can enforce peerages.Can our next-generation OS use both design patterns?!?
A Legitimised HierarchyAuditorIG2IG1OS Root AdministratorUsersChair of User Assurance GroupInspector-General (an elected officer)Each assurance group may want its own Audit (different scope, objectives, Trust, ).The OS Administrator may refuse to accept an Auditor.The OS Administrator makes a Trusting appointment when granting auditor-level Privilege to a nominee.Assurance organizations may be hierarchical, e.g. if the Users are governmental agencies or corporate divisions.
Summary of Static TrustThree types of trust: hierarchical, bridging, peering.Information flows are either trusted or privileged.Hierarchical trust has been explored thoroughly in the Bell-La Padula model.A subordinate actor is trusted to act appropriately, if a superior actor delegates some privileges.Bell-La Padula, when the hierarchy is mostly concerned about confidentiality.Biba, when the hierarchy is mostly concerned about integrity.A general purpose TC OS must support all concerns of a hierarchy.Actors have multiple personae.Bridging trust connects all an actors personae.A general purpose TC OS must support personae.Peering trust is a shared decision to trust an actor who is inferior to the peers.Peerages have trouble with enforcement; hierarchies have trouble with legitimation.A trusted OS must be a legitimate enforcement agent!
Dynamic Trust and System TrustWhen we join a hierarchy, form a bridge, or join a peerage, we make a trusting choice.We also make trusting choices when we leave a hierarchy, dismantle a bridge, or resign from a peerage.Hierarchies and peerages make trusting choices whenever they accept or reject a member.A trusted operating system should assist us with making, and recording, these structural operations: dynamic trust.Reputation systems could help us to make dynamic trust decisions, but they do not help us record these decisions.Current workflow systems have very little support for dynamic trust.System trust could be measured by our level of confidence in predicting the future behaviour of a hierarchical or peering system.
My GoalsI am trying to convene a broadly-representative group of purchasers to act as our governance body.Large corporations and governmental agencies have similar requirements for interoperability, auditability, static security, and multiple vendors.A first goal: develop buyers requirements for TC, DRM, and relationship management.International agreement and political buy-in is required if we are to have a system that is broadly acceptable.Regulatory requirements, such as protection of individual privacy, must be addressed.Law-enforcement and national-security requirements must also be addressed.A second goal: develop a trustworthy auditing process.The Jericho Forum has a congruent goal.It is developing buyers requirements for information security in large multinational corporations.However it is not a standards organisation, and it is not focussed on TC.The Jericho Forum is defining de-perimeterized security.
Some Members of Jericho
Jerichos De-perimeterized SecurityA corporate perimeter is not an easily-defendible security perimeter.A corporate perimeter defines a QoS boundary: performance, not security.We must harden our platforms, and our data objects, in order to take advantage of high connectivity and low cost of the internet.Jericho members want to make trustworthy connections on an untrusted network (the internet), between authenticated (and trustworthy) users with authenticated (and trustworthy) platforms.The connections must use open standards, to improve interoperability and integration, both within our own IT systems and with our business partners.
Organisation of the Jericho ForumUser members:Own the Forum;Vote on the deliverables;Run the Board of Managers.Vendor members:Have no votes;Participate fully in discussions.We now have 12 vendor members, and want more.Academic members:Offer their expertise in exchange for information of interest to their research.
The Jericho Commandments: Fundamentals (1-3)The scope and level of protection must be specific and appropriate to the asset at risk.Security mechanisms must be pervasive, simple, scalable, and easy to manage.Assume context at your peril: security solutions designed for one environment may not be transferable.The first two commandments are appropriate design goals for any secure system, including my vapourware TC.The third commandment suggests that there will be more than one TC OS, with differing levels of hardness. Well need help with our bridging trust across TC OSes!
Surviving in a Hostile WorldDevices and applications must communicate using open, secure protocols.All devices must be capable of maintaining their security policy on an untrusted network.My vapourware TC could use VPNs on hierarchical links.Implementing peerages on a completely untrusted network may be very difficult.
The Need for TrustAll people, processes, technology must have declared and transparent levels of trust for any transaction to take place.Mutual trust assurance levels must be determinable.These are requirements on dynamic trust in my TC OS.Decision support will take the form of an interoperable reputation system.These are also requirements on the use of an established bridge.For example, a company-confidential data object should not be transmitted over a bridge to a system that does not respect confidentiality.
Identity, Management and FederationAuthentication, authorisation and accountability must interoperate out of your area of control.My vapourware TC uses explicit bridges for interoperation.The devil will be in the details here... What control can be exerted, at reasonable cost, by a hierarchy over its members bridges?Workflow systems are very expensive and inflexible, suggesting that hierarchical control (= strong DRM) over bridges will be infeasible.I think we should focus on accountability rather than direct control over bridges.The TC OS should keep complete records of bridge creations (= relationship management).The TC OS should not keep records of bridge usage, except when highly confidential material is transferred.
Access to DataAccess to data should be controlled by security attributes of the data itself.Data privacy (and security of any asset of sufficiently high value) requires a segregation of duties/privileges.By default, data must be appropriately secured when stored, in transit and in use.These...