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- Peer-to-Peer Access Control Architecture Using Trusted
Computing Technology
- Ravi Sandhu and Xinwen Zhang
- SACMAT05, June 1--3, 2005, Stockholm, Sweden
With thanks to our Intel colleagues Kumar Ranganathan, Carlos
Rozas and Michael Covington 2. What is trust?
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- An entity can be trusted if it always behaves in the expected
manner for the intended purpose.
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- Trusted Computing Group (TCG)
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- Previously called Trusted Computing Platform Alliance
(TCPA)
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- Includes Intel, Microsoft, IBM, HP
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- A platform, or an application or service running on a
platform.
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- personal computer, personal digital assistant (PDA), smart
phone, etc.
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- A client is a computing platform that can initiate
communication with other clients to transfer or share data and
resources
3. Need Trust on the Client
- Traditional Client/Server Architecture
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- Trust is on the server side.
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- Trust is obtained with multi-layer protection mechanisms.
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- Intrusion detection and intrusion prevention systems
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- There is little trust on client side.
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- Clients are generally lightly protected.
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- Ubiquitous connectivity in clients
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- Attacks outpacing todays protection models
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- Attack tools readily available
- Information resident on the client becomes susceptible to
software-based attacks.
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- Mismatch between security and high value of data in client
platforms.
4. Trusted Computing Technology
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- software alone cannot provide an adequate foundation for trust
on the client
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- Capability-based computers
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- Trust with security kernel based on military-style security
labels
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- Orange Book, eliminate trust from applications
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- Hardware and crypto-based root of trust
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- No Trojan Horses, ergo no covert channels
Little participation from academia or larger research community
5. Trusted Computing
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- TCG Specifications of TPM (Trusted Platform Module)
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- TPM is hardware root of trust
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- therefore a performance bottleneck
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- Intels LaGrande Technology (LT)
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- Microsoft Palladium -> NGSCB -> ??
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- Linux, SE Linux, Trusted BSD
6. Trusted Platform Module (TPM)
Adapted from TCG presentation MCH ICH AGP Network Port LPC TPM
CPU RAM BIOS TPM is connected to the motherboard 7. TPM
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- Non-Migratable Keys :Permanently bound specific TPM, i.e.,
platform
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- Migratable Keys: Can be migrated to other platforms
From TCG presentation Storage Root Key (SRK) Non-Migratable
Storage Key Migratable Storage Key Endorsement Key Migratable
Storage Key Migratable Signing Key Migratable Signing Key
Non-Migratable Storage Key Non-Migratable Signing Key Migratable
Signing or Storage Key Attestation ID Keys Migratable Signing or
Storage Key Protected by the RTS Protected by the TPM 8.
Attestation From Intel presentation 9. Intels LaGrande Technology
(LT)
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- Protected graphics and memory management
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- Enforce policy for protected memory
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- Currently DMA bypasses memory protection
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- Sleep mode on laptops looses memory protection guarantee
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- Trusted channel between keyboard/mouse and trusted
software
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- Provide platform authentication and attestation
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- Existing ring 0 has too much stuff in it (principally device
drivers)
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- Rings 1 and 2 unused, everything outside OS kernel runs in ring
3
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- New ring -1 privileged beyond OS kernel
10. Contributions of this paper
- 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
11. Motivating Applications
- Trust on client needed in emerging applications
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- Information Sharing (sometimes called Dissemination Control or
DCON)
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- 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
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- Realtime protection of audio data in a platform
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- conversation is not eavesdropped or illegally recorded.
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- Forward control of audio object (e.g., voice mail)
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- control the platform and user to forward
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- electronic currency between peer platforms
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- payment systems for p2p e-commerce (e.g., m icropayment,
mobile-payment)
12. Architecture
- Platform with trusted reference monitor (TRM)
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- Tamper resistent hardware
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- A homogeneous environment
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- Each platform is equipped uniformly with necessary TC
hardware.
13. Available Credentials
- TPM AIK pair(PK TPM.AIK , SK TPM.AIK )
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- private key is protected by a TPM with SRK.
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- Public key is certified by a privacy CA.
- TRM key pair(PK TRM ,SK TRM )
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- The private key is protected by the TPM.
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- The public key is certified by AIK.
- Application key pair(PK APP ,SK APP )
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- Either the SRK of a TPM, or a key protected by the SRK
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- Protect secrets and policies
14. Functions of TRM
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- seals dataxby TRM withintegrity measurement ofH(TRM).
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- xcan only be unsealed under this TRM when the corresponding PCR
value isH(TRM).
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- In practical a set of PCRs may be included.
- TRM.Attest(H(TRM), PK TRM )
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- Return {H(TRM) || PK TRM }SK_TPM.AIK
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- Attestation response signed by AIK of TPM
15. Architecture
- Policy and Secret Distribution:
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- Each object has a policy.
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- Object is encrypted with secret key before distribution.
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- Policy specifies what platform and application can access this
object
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- migratable or non-migratable policy
16. Architecture
- Policy Enforcement in a client platform
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- Only valid TRM can unseal the policy info and secret.
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- This valid TRM (specified by integrity measurement) can enforce
the policy.
17. Revocation
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- Trust revocation of a requesting application
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- Trust revocation of a TRM
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- Trust revocation of a platform
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- Push: Object owner sends updated policy to client side
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- Pull: client side check policy update from object owner
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- Both may have delayed revocation
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- Instant revocation needs centralized policy server
18. Support User Attributes
- Each platform has a user agent (UA)
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- Controlled by platform administrator
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- A key pair(PK UA ,SK UA )
- Each user has an identity key pair(PK u , SK u )
- Identity and role certificates:
19. Support User Attribute
- Binding of identity and role certificates
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- tightly-coupled binding: by signature
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- loosely-coupled binding: by other components
20. Support User Attribute
- Role-based policy enforcement:
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- TRM sends attestation challenge message to the UA.
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- UA responds with attestation information.
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- If the TRM trusts the running UA, it sends requesting message
for role information of the user.
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- The UA sends back the role certificate of the user.
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- UA may submit the proof-of-possession for the corresponding
private key of the identity public key
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- Mutual attestation may be needed
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- UA needs to ensure that TRM does not release role
information.
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- Role certificate is private information of a user.
21. Support User Attribute
- Migration of User Credentials
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- Identity credential and role credential are migratable.
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- Not bounded to specific platform
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- Can be moved or copied between platforms
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- Destination platforms determined by identity owner (user)
22. Applications
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- Realtime Protection of Conversation
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- Secure channel between VOIP software and device driver
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- Attestation between TRM and VOIP software
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- Attestation between TRM and UA
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- Attestation between TRM and device driver
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- Secure Storage and Forward of Voice Mail
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- A policy specifying authorized platform and user attribute
23. Related Work Includes
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- Arbaugh et al., Oakland97
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- Boot only signed and verified software
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- IBM 4758 crypto coprocessor
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- Closed system to run certified and signed software
- Behavior-based attestation
- Trusted operating systems
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- SELinux, Trusted Solaris, TrustedBSD
- Attestation-based policy enforcement
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- Controlled access from client to server by attesting client
platform
24. Conclusion
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- Architecture with TC to support peer-to-peer based access
control
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- General architecture for client-side access control
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- Consider trust of platforms and applications in access control
policy
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- Integrate user attributes in TC
- Future work opportunities include:
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- TPM is highly performance challenged
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- Access control model with TC
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- Fit in some component of existing models?
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- Consider other applications
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- Ubiquitous and pervasive computing environments
25. OM-AM
What? How? A s s u r a n c e TPM, LT, PKI Information Sharing,
VoIP, etc This paper focuses here Future work