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PoWah Yau, Allan Tomlinson, Shane Balfe and Eimear Gallery

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Title: PoWah Yau, Allan Tomlinson, Shane Balfe and Eimear Gallery


1
Applying Trusted Computing to a Workflow System
  • Po-Wah Yau, Allan Tomlinson, Shane Balfe and
    Eimear Gallery
  • Information Security Group
  • Royal Holloway, University of London
  • www.isg.rhul.ac.uk

Third e-Science Workshop Trusted Services
Requirements and Prospects, 8-9 July 2008,
Edinburgh
2
Contents
  • Introduction
  • Grid workflow security
  • Overview of Trusted Computing
  • Securing workflows
  • Summary

3
Introduction
  • Grid middleware used to achieve synergy from
    otherwise disparate resources
  • Hardware (CPU, storage, computationally steerable
    equipment),
  • Applications,
  • Data, and
  • People.
  • Security issues when running a Grid job at a
    resource provider
  • See Andys talk!

4
Introduction
  • Grid workflows used to achieve automated synergy
    from multiple tasks
  • Logical ordering of tasks,
  • Each task can either process results of another
    task or new set of data,
  • Sequential, parallel, choice branching and loops.
  • Variety of workflow systems
  • Low level, physical workflows, as opposed to
  • High level (e.g. Pegasus, P-Grade, Taverna).

5
Introduction
  • Workflow Resource Broker (WRB)
  • Typically maps abstract workflow of tasks to
    physical workflow of jobs (in a high level
    system),
  • Selects resource providers to run jobs (according
    to static requirements), and
  • Schedules jobs (taking into account dynamic
    requirements).

6
Contents
  • Introduction
  • Grid workflow security
  • Overview of Trusted Computing
  • Securing Grid workflows
  • Summary

7
Grid Workflow Security
  • Confidentiality, to protect
  • An individual job,
  • A workflow of jobs,
  • The workflow/sub-workflow, and
  • The locations of where jobs are submitted.
  • Integrity, to prevent
  • Error propagation,
  • Wasted resources, and
  • Loss of reputation.

8
Grid Workflow Security
  • WRB vulnerabilities
  • Delegated control of user credentials
  • Resource provider selection
  • Scheduling and location of workflow jobs
  • Resource provider vulnerabilities
  • Complex Grid middleware
  • Local user access
  • Network vulnerabilities

9
Contents
  • Introduction
  • Grid workflow security
  • Overview of Trusted Computing
  • Securing Grid workflows
  • Summary

10
Overview of Trusted Computing
  • Defined by the Trusted Computing Group
  • www.trustedcomputinggroup.org
  • A Trusted Platform consists of
  • Trusted Platform Module (TPM) embedded into the
    host platform,
  • Protected capabilities, commands, that can access
    shielded locations (memory, registers), and
  • Creating proxy roots of trust in hardware.

11
Overview of Trusted Computing
  • Three types of key
  • Non-migratable keys never leave protection of the
    TPM in which they are created, and are certified
    by the TPM.
  • Migratable keys can be released by a TPM,
    encrypted using the public key of the
    destination, but are not certified.
  • Certifiable migratable keys are keys that are
    migrated under specific conditions, possibly
    under the control of a Migration Selection
    Authority (MSA).

12
Overview of Trusted Computing
  • Each TPM is shipped with a non-migratable
    Endorsement Key.
  • A non-migratable Storage root key (SRK) is
    created when a TPM is initialised/reset
  • The SRK is used to encrypt other keys, which can
    then be stored outside of the TPM,
  • If a non-migratable key is used to encrypt data,
    then that data is bound to the TPM, and
  • If use of that non-migratable key is only
    possible when the platform is in a specific
    state, then that data is sealed to that
    platform state.

13
Overview of Trusted Computing
  • Integrity measurement
  • The ability to record events that modify platform
    state, which are
  • Stored in Platform Configuration Registers (PCRs)
    via an extend operation.
  • Sealed storage
  • Binding data objects, including cryptographic
    keys, to a specific platform state.
  • Attestation
  • The ability to prove platform state to an
    external entity, where
  • The PCR values are signed using an Attestation
    Identity Key (AIK).

14
Contents
  • Introduction
  • Grid workflow security
  • Overview of Trusted Computing
  • Securing Grid workflows
  • Assumptions
  • Workflow preparation
  • Workflow execution
  • Summary

15
Securing Grid Workflows
  • The following proposal uses Trusted Computing to
    provide
  • Trusted resource provider selection
  • Confidentiality of job information
  • Integrity of job information
  • Secondary properties
  • Confidentiality and integrity of workflow
  • Information to possibly assist process provenance

16
Assumptions
  • Trusted Computing prevalence
  • WRB platform
  • Subset of resource providers
  • Means of verifying that WRB can be trusted
  • User has a means of specifying high level
    security requirements
  • Translated by WRB into low-level platform state
    requirements

17
Assumptions
  • All resource providers have a certified copy of
    the WRBs public signature verification key.
  • The WRB has a copy of all resource providers
    public signature verification key.

18
Workflow preparation (1)
  • Consider a workflow of jobs a0, a1, , an
  • Each job ai is associated with a symmetric key
    Ki, which will be used to protect the job.
  • A private key SKi is also associated with each
    job ai
  • This will be stored in a TPM.

19
Workflow preparation (1)
  • The resource provider RPi can obtain SKi using
    one of two methods
  • The WRB creates a certifiable migratable key pair
  • Specifying the state ?i to which the private key
    is sealed
  • The key is then migrated to TPM of RPi
  • RPi creates a non-migratable key pair sealed to a
    specific platform state ?i
  • The public key and platform state are advertised
    as part of an attestation token Lohr et al. 06

20
Workflow preparation (2)
  • WRB ?? RPi

21
Workflow preparation (2)
  • WRB ?? RPi IDW
  • Identifiers of WRB and workflow

22
Workflow preparation (2)
  • WRB ?? RPi IDW ri
  • Random nonce

23
Workflow preparation (2)
  • WRB ?? RPi IDW ri gKi (ai r i)
  • Output of g is the ciphertext and
  • message authentication code
  • for the job and nonce

24
Workflow preparation (2)
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki)
  • Ki encrypted using PKi corresponding to
  • SKi which is sealed to platform state ?i

25
Workflow preparation (2)
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • Identifier of resource provider RPi1 to send job
    results to, and
  • Public encryption key of RPi1 corresponding to
    Ski1

26
Workflow preparation (2)
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1
  • Identifier of preceding resource provider,
  • Public verification key of RPi-1 (non-TPM key),
  • The platform state of RPi-1 required by WRB

27
Workflow preparation (2)
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • The WRBs digital signature on the whole message

28
Workflow preparation (2)
  • In summary
  • Each job is protected using a symmetric key,
  • This key is sealed to the required platform
    state,
  • The platform states to which the keys are sealed
    are decided/known before workflow execution, and
  • Each resource provider knows the state that the
    previous resource provider should have been in,
    in order to execute their designated job.

29
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1

30
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi Verify ?W and ?RPi-1
  • RPi Retrieve Ki using SKi (sealed to TPM)
  • RPi Decrypt and retrieve ai , and verify
    integrity

31
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi

32
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi Generate random nonce
  • RPi Send attestation challenge

33
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi

34
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi IDW F(?i-1, rRPi)
  • RPi-1 Generates response to attestation
    challenge

35
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi IDW F(?i-1, rRPi)
  • RPi-1 Generates symmetric key Ki and

36
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi IDW F(?i-1, rRPi)
  • gKi (R(ai-1, rRPi) rRPi)
  • RPi-1 Protects job results using Ki

37
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi IDW F(?i-1, rRPi)
  • gKi (R(ai-1, rRPi) rRPi)
  • ePKi (Ki)
  • RPi-1 Encrypts Ki using public key PKi

38
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi IDW F(?i-1, rRPi)
  • gKi (R(ai-1, rRPi) rRPi)
  • ePKi (Ki)
  • RPi Verifies F(?i-1, rRPi)

39
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi IDW F(?i-1, rRPi)
  • gKi (R(ai-1, rRPi) rRPi)
  • ePKi (Ki)
  • RPi Retrieves Ki

40
Workflow execution
  • WRB ?? RPi IDW ri gKi (ai r i)
  • ePKi (Ki) IDi1 PKi1
  • IDRPi-1 VKRPi-1 ?i-1 ?W
  • RPi-1 ?? RPi IDW ready ?RPi-1
  • RPi-1 ?? RPi IDW C(rRPi)
  • RPi-1 ?? RPi IDW F(?i-1, rRPi)
  • gKi (R(ai-1, rRPi) rRPi)
  • ePKi (Ki)
  • RPi Recovers ai-1, and processes ai

41
Workflow execution
  • In summary
  • Job are protected using a symmetric key,
  • This key is sealed to the required platform state
    of the next resource provider in the workflow,
  • A resource provider should challenge the previous
    one to attest to its platform state.

42
Properties of the scheme
  • Security is provided in both directions of a
    workflow
  • Forward trusted resource provider selection,
  • Backward detection of compromised jobs.
  • Efficient symmetric key cryptography to protect
    job data
  • Symmetric key bound to trusted platform state,
    via sealed private key.
  • Each platform stores a secure measurement log
  • Potentially useful (verifiable) information for
    process provenance.

43
Summary
  • Securing Grid workflows is paramount because a
    users entire dataset is being exposed.
  • Trusted computing can be used to improve trust
    establishment in Grids.
  • Trust in the Workflow Resource Broker is
    critical.
  • Proposed a scheme to ensure trusted workflow
    execution.

44
Acknowledgements
  • The first and second authors are being funded by
    the Engineering and Physical Sciences Research
    Council (EPSRC) UK e-Science programme of
    research (EP/D053269).
  • The third author is sponsored by the U.S. Army
    Research Laboratory and the UK Ministry of
    Defence (Agreement no. W911NF-06-3-0001)
  • The fourth author is sponsored by the Open
    Trusted Computing project of the European
    Commission Framework 6 Programme.
  • Thanks to Professor Chris J. Mitchell.
  • For more details of this project please refer to
    www.distributedtrust.org.

45
Thank you for listening
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