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Peer-to-Peer Access Control Architecture Using Trusted Computing Technology Ravi Sandhu and Xinwen Zhang George Mason University SACMAT05, June 1--3, 2005, Stockholm, Sweden. With thanks to our Intel colleagues Kumar Ranganathan, Carlos Rozas and Michael Covington. What is trust?. Trust

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Peer-to-Peer Access Control Architecture Using Trusted Computing Technology

Ravi Sandhu and Xinwen Zhang

George Mason University

SACMAT05, June 1--3, 2005, Stockholm, Sweden

With thanks to our Intel colleagues Kumar Ranganathan, Carlos Rozas and Michael Covington

What is trust
What is trust? Computing Technology

  • Trust

    • “An entity can be trusted if it always behaves in the expected manner for the intended purpose.”

    • Trusted Computing Group (TCG)

      • Previously called Trusted Computing Platform Alliance (TCPA)

      • Includes Intel, Microsoft, IBM, HP

  • Entity

    • A platform, or an application or service running on a platform.

      • personal computer, personal digital assistant (PDA), smart phone, etc.

    • A client is a computing platform that can initiate communication with other clients to transfer or share data and resources

Need trust on the client
Need Trust on the Client Computing Technology

  • Traditional Client/Server Architecture

    • Trust is on the server side.

    • Trust is obtained with multi-layer protection mechanisms.

      • Access control

      • Firewall

      • Intrusion detection and intrusion prevention systems

    • There is little trust on client side.

      • Clients are generally lightly protected.

      • Ubiquitous connectivity in clients

      • Attacks outpacing today’s protection models

      • Attack tools readily available

  • Information resident on the client becomes susceptible to software-based attacks.

    • Mismatch between security and high value of data in client platforms.

Trusted computing technology
Trusted Computing Technology Computing Technology

  • Basic premise

    • software alone cannot provide an adequate foundation for trust on the client

  • Old style TC

    • Multics system

    • Capability-based computers

      • Intel 432

    • Trust with security kernel based on military-style security labels

      • Orange Book, eliminate trust from applications

  • What’s new

    • Hardware and crypto-based root of trust

      • Ubiquitous availability

    • Trust within a platform

    • Trust across platforms

    • Trust in applications

      • No Trojan Horses, ergo no covert channels

Little participation

from academia or larger

research community

Trusted computing
Trusted Computing Computing Technology

  • Recent TC activities:

    • TCG Specifications of TPM (Trusted Platform Module)

      • TPM is hardware root of trust

      • Needs to be ubiquitous

        • cheap, cheap, cheap

        • therefore a performance bottleneck

    • Additional Hardware

      • Intel’s LaGrande Technology (LT)

      • ARM TrustZone

    • OS/Software

      • Microsoft Palladium -> NGSCB -> ??

      • Linux, SE Linux, Trusted BSD

        • Mostly NSA funded

    • Supporting PKI

Trusted platform module tpm

Adapted from TCG presentation Computing Technology

TPM is connected to the motherboard











Trusted Platform Module(TPM)

  • Specified by TCPA/TCG

  • “Smartcard” on board

From TCG presentation Computing Technology

Protected by the TPM

Storage Root Key(SRK)

Endorsement Key

Protected by the RTS

Non-Migratable Storage Key

Migratable Storage Key

Attestation ID Keys

Non-Migratable Storage Key

Non-Migratable Signing Key

Migratable Storage Key

Migratable Signing Key

Migratable Signing Key

Migratable Signing or Storage Key

Migratable Signing or Storage Key


  • Key Hierarchy

    • Non-Migratable Keys :Permanently bound specific TPM, i.e., platform

    • Migratable Keys: Can be migrated to other platforms


From Intel presentation Computing Technology


Intel s lagrande technology lt
Intel’s LaGrande Technology (LT) Computing Technology

  • LT includes:

    • Chipset

      • Protected graphics and memory management

    • Extended CPU:

      • Enable domain separation

      • Enforce policy for protected memory

        • Currently DMA bypasses memory protection

        • Sleep mode on laptops looses memory protection guarantee

    • Protected I/O:

      • Trusted channel between keyboard/mouse and trusted software

    • TCG TPM v1.2

      • Protect keys

      • Provide platform authentication and attestation

    • Ultra privileged ring -1

      • Existing ring 0 has too much stuff in it (principally device drivers)

      • Rings 1 and 2 unused, everything outside OS kernel runs in ring 3

      • New ring -1 privileged beyond OS kernel

Contributions of this paper
Contributions of this paper Computing Technology

  • Integrate user attributes into TC architecture

  • Support a user's ability to roam between platforms by migrating user identities and attribute certificates

  • Consider specific applications

Motivating applications
Motivating Applications Computing Technology

  • Trust on client needed in emerging applications

    • Information Sharing (sometimes called Dissemination Control or DCON)

      • Health records of a patient may be transmitted from a primary physician to a consultant who can access them for some limited period of time and cannot transmit them to anyone else

    • P2P VOIP application

      • Realtime protection of audio data in a platform

        • conversation is not eavesdropped or illegally recorded.

      • Forward control of audio object (e.g., voice mail)

        • control the platform and user to forward

    • M-commerce

      • electronic currency between peer platforms

      • payment systems for p2p e-commerce (e.g., micropayment, mobile-payment)

Architecture Computing Technology

  • Platform with trusted reference monitor (TRM)

  • Assumptions:

    • Tamper resistent hardware

    • A homogeneous environment

      • Each platform is equipped uniformly with necessary TC hardware.

Available credentials
Available Credentials Computing Technology


    • private key is protected by a TPM with SRK.

    • Public key is certified by a privacy CA.

  • TRM key pair (PKTRM,SKTRM)

    • The private key is protected by the TPM.

    • The public key is certified by AIK.

  • Application key pair (PKAPP,SKAPP)

    • Similar to TRM key pair

  • TPM storage key(s)

    • Either the SRK of a TPM, or a key protected by the SRK

    • Protect TRM's credential

    • Protect secrets and policies

Functions of trm
Functions of TRM Computing Technology

  • TRM.Seal(H(TRM),x):

    • seals data x by TRM with integrity measurement of H(TRM).

    • x can only be unsealed under this TRM when the corresponding PCR value is H(TRM).

    • In practical a set of PCRs may be included.

  • TRM.GenerateKey(k)

    • generates a secret key k

  • TRM.Attest(H(TRM), PKTRM)

    • Return {H(TRM) || PKTRM} SK_TPM.AIK

    • Attestation response signed by AIK of TPM

Architecture Computing Technology

  • Policy and Secret Distribution:

    • Each object has a policy.

    • Object is encrypted with secret key before distribution.

    • Policy specifies what platform and application can access this object

      • migratable or non-migratable policy

Architecture Computing Technology

  • Policy Enforcement in a client platform

    • Only valid TRM can unseal the policy info and secret.

    • This valid TRM (specified by integrity measurement) can enforce the policy.

Revocation Computing Technology

  • Revocation because of

    • Trust revocation of a requesting application

    • Trust revocation of a TRM

    • Trust revocation of a platform

  • Two approaches:

    • Push: Object owner sends updated policy to client side

    • Pull: client side check policy update from object owner

    • Both may have delayed revocation

    • Instant revocation needs centralized policy server

Support user attributes
Support User Attributes Computing Technology

  • Each platform has a user agent (UA)

    • Controlled by platform administrator

    • A key pair (PKUA,SKUA)

  • Each user has an identity key pair (PKu, SKu)

    • Migratable key

  • Identity and role certificates:

Support user attribute
Support User Attribute Computing Technology

  • Binding of identity and role certificates

    • tightly-coupled binding: by signature

    • loosely-coupled binding: by other components

Support user attribute1
Support User Attribute Computing Technology

  • Role-based policy enforcement:

    • TRM sends attestation challenge message to the UA.

    • UA responds with attestation information.

    • If the TRM trusts the running UA, it sends requesting message for role information of the user.

    • The UA sends back the role certificate of the user.

      • UA may submit the proof-of-possession for the corresponding private key of the identity public key

    • Mutual attestation may be needed

      • UA needs to ensure that TRM does not release role information.

      • Role certificate is private information of a user.

Support user attribute2
Support User Attribute Computing Technology

  • Migration of User Credentials

    • Identity credential and role credential are migratable.

      • Not bounded to specific platform

      • Can be moved or copied between platforms

    • Destination platforms determined by identity owner (user)

Applications Computing Technology

  • Secure VOIP:

    • Realtime Protection of Conversation

      • Secure channel between VOIP software and device driver

      • Attestation between TRM and VOIP software

      • Attestation between TRM and UA

      • Attestation between TRM and device driver

    • Secure Storage and Forward of Voice Mail

      • A policy specifying authorized platform and user attribute

      • Similar to DCON

Related work includes
Related Work Includes Computing Technology

  • Secure Boot:

    • Arbaugh et al., Oakland97

    • Boot only signed and verified software

  • Secure coporcessors

    • IBM 4758 crypto coprocessor

    • Closed system to run certified and signed software

  • Behavior-based attestation

    • Haldar et al. USENIX04.

    • Trusted VM

  • Trusted operating systems

    • SELinux, Trusted Solaris, TrustedBSD

  • Attestation-based policy enforcement

    • Sailer et al. CCS04

    • Controlled access from client to server by attesting client platform

Conclusion Computing Technology

  • Summary

    • Architecture with TC to support peer-to-peer based access control

    • General architecture for client-side access control

    • Consider trust of platforms and applications in access control policy

    • Integrate user attributes in TC

  • Future work opportunities include:

    • Performance

      • TPM is highly performance challenged

    • Access control model with TC

      • A new model?

      • Fit in some component of existing models?

    • Consider other applications

      • P2P and Ad Hoc networks

      • Grid systems

      • Ubiquitous and pervasive computing environments

      • Information sharing

      • Digital home

Om am
OM-AM Computing Technology










  • Objectives

  • Model

  • Architecture

  • Mechanism


Information Sharing,

VoIP, etc

Future work

This paper focuses here