1. Towards Accountable Management of Identity and Privacy: Sticky Policies and Enforceable Tracing Services
Marco Casassa Mont
Siani Pearson
Pete Bramhall
Trusted Systems Laboratory
Hewlett-Packard Labs, Bristol, UK
TrustBus 2003, 2-4 September 2003
Prague, Czech Republic

2. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Presentation Outline
Setting the Context
Scenario
Addressed Problems
Related Work
Our Approach
Discussion
Conclusions
25/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

3. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Setting the Context
Digital Identities and Profiles are relevant to
enable transactions and interactions on the web,
in many contexts: personal, social, business,
government, etc.
Privacy Management is a major issue: involves people,
organisations, governments, etc.
Different reactions by people: ranging from “completely
ignoring the privacy issues” to “being so concerned
to prevent any web interaction”
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

4. Scenario: Multiparty Interactions [1]
Multiparty Transaction
/ Interaction
Services
User
Negotiation of
Privacy Policy
Services
Enterprise
Policies
Provision of
Identity & Profile
Data
Data
Identity/
Profile
Disclosure
Services
Enterprise
Enterprise
Similar issues in the e-Commerce, Enterprise, Financial and Government Areas
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

5. Scenario: Multiparty Interactions [2]
Little has been done so far to directly involve people
(or third parties acting on their behalf) in the
management of their privacy
Users lack control over their personal information
after their initial disclosures
Organisations, as well, lack control over the
confidential information they manage on behalf of
their customers, once they disclose it to third parties
It is hard to make organisations accountable
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

6. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Addressed Problems
Privacy Enforcement
Accountability of Organizations
Involvement of People in the Management
of their Personal Data
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

7. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [1]
Lot of work done to provide
Legislative Frameworks for Privacy
Different legislative approaches: example US vs. EU
Privacy and Data Protection laws are hard to enforce
when personal information spreads across boundaries
In general users have little understanding or
knowledge of privacy laws and their implications
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

8. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [2]
W3C approach on Platform for Privacy Preferences
(P3P): simple policies, point-to-point interactions. Little
control on the fulfilment of these policies (at least,
in the current implementations)
Liberty Alliance and Microsoft Passport: Identity and
Privacy Management based on closed web of trust
and predefined policies
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

9. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [3]
IBM’s work on Enterprise Privacy Authorization Language
(EPAL) and related Privacy Framework
Association of fine-grained Privacy Policies (Sticky Policies)
to personal data. Enforcement of Privacy Polices by the Enterprise
Current Open Issues:
- Policy “Stickiness” is not enforceable;
- Too much trust in the enterprise;
- Leakages of personal data can still happen;
- Little user’s involvement.
The above issues are very hard to address!
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

10. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Our Approach
About a Privacy and Accountability Model encompassing:
“Sticky” Privacy Policies strongly associated to
Identity Information
Mechanisms for strong (but not impregnable)
enforcement of privacy policies
Mechanisms to increase the Accountability of the
involved parties
Mechanisms to allow people to be more involved
in the management of their data (if they want to …)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

11. Privacy and Accountability Model
Key aspects:
Confidentiality of Data: obfuscation of confidential data
Strong Association of Privacy Policies to Confidential Data:
- “tamper resistant” policies associated to data.
- “Stickiness” guaranteed at least till the first disclosure.
Policy Compliance Check and Enforcement: by trusted
Tracing & Auditing Authorities (TAAs) and Trusted Platforms + OSs
Accountability Management: auditing and tracing of
disclosures by TAA (used as evidence)
User Involvement: policy authoring, notification, authorization
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

12. Privacy and Accountability Model [1]
User
Enterprise
Multiparty Transaction
/ Interaction
Policies
Data
Services
Negotiation of
Privacy Policy 1
Request for Authorization or
Notification 5
Obfuscated Data +
Sticky Privacy
Policies
Sticky 2
Obfuscated Data +
Sticky Privacy
Policies 8
Decryption Key
(if Authorised) 6
Request for Disclosure of Data +
Sticky Privacy Policies
Credentials 3
Checking for
Integrity and
Trustworthiness of
Remote Environment 4 6 ? ?
Tracing and Auditing Authorities (TAAs) 7
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

13. Privacy and Accountability Model [2]
Once confidential data is disclosed it can still be misused …
Risks Mitigation via:
Audit trail:
Audit logs managed by TAAs can be used as Evidence and
for Forensic Analysis (logging at least the first disclosure …)
Trusted Platforms and OSs:
- checking for the Integrity of the Receivers’ environment
- enforcing part of the Privacy Policies directly at
the OS level. Research and Work in Progress …
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

14. Privacy and Accountability Model: Technical Aspects [1]
A technical implementation of our Privacy and Accountability Model leverages three key technologies:
Identifier-based Encryption (IBE)
Trusted Platforms (TCG was TCPA, etc.)
Tagged Operating Systems (OSs)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

15. What is Identifier-based Encryption (IBE)?
It is an Emerging Cryptography Technology
Based on a Three-Player Model: Sender, Receiver, Trust Authority (Trusted Third Party)
Same Strength of RSA
Different Approaches: Quadratic Residuosity, Weil Pairing, Tate Pairing …
SW Library and Technology available at HP Laboratories
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

16. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
IBE Core Properties
1st Property: any kind of “string” (or Sequence of Bytes) can be used as an IBE Encryption Key: for example a Role, an Address, a Picture, a Disclosure Time, Terms and Conditions,
a Privacy Policy …
2nd Property: the generation of IBE Decryption Keys can be postponed in time, even long time after the generation of the correspondent IBE Encryption Key
3rd Property: reliance on at least a Trust Authority (Trusted Third Party) for the generation of IBE Decryption Key
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

17. IBE Three-Player Model
Alice
Trust
Authority
Bob
4. Alice Sends the encrypted Message
to Bob, along with the Encryption Key 4
2. Alice knows the Trust Authority's
published value of Public Detail N
It is well known or available from
reliable source 2
3. Alice chooses an appropriate Encryption
Key. She encrypts the message:
Encrypted message
= {E(msg, N, encryption key)} 3
5. Bob requests the Decryption
Key associated to the
Encryption Key to the relevant
Trust Authority. 5
6. The Trust Authority issues
an IBE Decryption Key
corresponding to the supplied
Encryption Key only if it is
happy with Bob’s
entitlement to the Decryption Key.
It needs the Secret to perform the
computation. 6
1. Trust Authority
- Generates and
protects a Secret
- Publishes a
Public Detail N 1
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

18. Privacy and Accountability Model: Technical Aspects [2]
A technical implementation of our Privacy and Accountability Model leverages three key Technologies:
Identifier-based Encryption (IBE)
Trusted Platforms (TCG was TCPA, etc.)
Tagged Operating Systems (OSs)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

19. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Trusted Platforms
A trusted platform provides hardware mechanisms (TPM) and tools to check for the integrity of computer platforms and their installed software (locally and remotely)
TCG (was TCPA) and Microsoft NGSCB initiatives:
HP and HP Laboratories are directly involved in the TCG initiative
TPM
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

20. Privacy and Accountability Model: Technical Aspects [3]
A technical implementation of our Privacy and Accountability Model leverages three key Technologies:
Identifier-based Encryption (IBE)
Trusted Platforms (TCG was TCPA, etc.)
Tagged Operating Systems (OSs)
25/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

21. Tagged Operating Systems
A tagged Operating System
(OS) provides mechanisms and
tools to associate low level labels
to data and directly enforce and
manage them at the OS level.
The “stickiness” of a label to
the content, not to the content
holder (such as a file), ensures that
even when the data is copied
around the label follows it as well.
Labels can be associated
(at the OS level) to low level
Privacy Policies (rules),
directly enforced by the OS.
Rules dictate constraints on: copies of
data, data transmissions, etc.
A working prototype is available
at HP Laboratories, Bristol.
Policy Creation and Translation System
policies created in dflow
compiler
Policy
File in
Internal
Format
Control Enforcement
Tagged Data
Decision
Policy evaluation engine
Flow causing operation
yes, no, more checks
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

22. Privacy and Accountability Model: Technical Aspects [4]
- (High level) Stickiness of Privacy Policies
User Involvement
Accountability Management
- Enforcement of Aspects of Privacy Policy
Addressed Problems
(Low level) Source of Trust and
HW/SW integrity checking
- (Low level) Stickiness of Privacy Policies
Technologies
Trusted Platforms (TCG …)
Tagged OSs
Our Privacy and
Accountability Framework
(IBE, TAAs, etc.)
GAP
GAP
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

23. High-level System Architecture
Based on the IBE Model
Privacy Policies are
represented as
“IBE Encryption Keys”
Confidential data is
encrypted with IBE
encryption keys
IBE encryption keys
“stick” with the encrypted
data (at least till the first
de-obfuscation of the data …)
The “Tracing and Auditing
Authority” is an (IBE based)
Trust Authority.
Leveraging Trusted Platforms and
Tagged OS for enforcing aspects
of Privacy Policies
(Work in Progress…)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

24. Sticky Privacy Policies
Example of high-level Sticky Policy (XML format):
Reference to TA(s)
Constraints/
Obligations
Platform
Constraint
Actions
(User Involvement)
IBE encryption keys can define any kind of privacy constraints or terms and conditions to
be deployed and enforced at different levels of abstractions (application/service, OS, platform)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

25. Enforcement of Sticky Privacy Policies
Enterprise 1
Personal Data
Policy Engine
Sticky
Privacy Policies
TCG
Tagged OS
TCG
Enterprise 2
Enforcement
via
Trust Authority +
TCG
Tagged OS
TCG
Policy Engine
Enforcement
By Trusted
Platforms and
Tagged OS
(Work in Progress)
TCG
Tagged OS
TCG
Policy Engine
Trust Authority (TA)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

26. Policy Enforcement by Trust Authority
“Soft” policy enforcement: TA still
relies on the receiver to take care of the
data privacy, once data is disclosed …
The TA interprets Privacy Policies via a Policy Engine
The TA makes sure that the Privacy Policies are satisfied
before issuing the IBE decryption key
Multiple TAs can be used, each of them specialised in
doing specific checks (easy with IBE-based approach …)
Users can be notified or asked for authorization, if
the Privacy Policies require it (User Involvement)
Audit of disclosures, at least the first time …
The TA can leverage TCG and Tagged-OS to make sure
that part of the policy enforcement is done upfront …
Enterprise 1
Privacy
Policies
Enterprise 2
Privacy
Policies
Trust Authority (TA)
25/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

27. Policy Enforcement by Trusted Platforms
Stronger Enforcement of part of the privacy policies
(low level policies)
TCG integrity checking mechanisms checks for
platform trustworthiness along with
its SW and HW integrity. Cross boundaries
integrity checking on the platforms of the involved parties
To be effective, a widespread usage of
trusted platforms is required. At least all the
platforms involved in the task of processing
confidential data should be checked.
Some of them might not be exposed externally.
 Too strong requirements for the time being …
 Limits on the kinds of HW and SW checks …
Joint usage of Tagged-OS and TCG to create Trust Domains.
TCG to check upfront the integrity of the “combined” system.
Tagged-OS to enforce privacy policies directly at the OS level:
disallow copies data, sending data only to specific IP addresses, etc.
Enterprise 1
Trust Domain
Privacy
Policies
Enterprise 2
Tagged OS
TCG
Tagged OS
TCG
Tagged OS
TCG
Tagged OS
TCG
Tagged OS
TCG
Tagged OS
TCG
Trust Authority (TAA)
Research and Work in Progress …
25/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

28. Accountability Management
Confidential data is encrypted:
at least the first time the requestors
need to interact with the Tracing
and Auditing Authorities (TAAs)
Auditing and Logging of data disclosures
carried on by TAAs (at least the first time)
Multiple TAAs can be used to mitigate trust issues.
Users can run their own TAAs
Usage of Audit Logs as Evidence and
for Forensic Analysis
Research in progress at HP Labs on
tamper-resistant audit systems
Enterprise 1
Privacy
Policies
Privacy
Policies
Enterprise 2
Trust Authorities (TAAs)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

29. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Discussion
The usage of “trusted third parties” to mediate interactions and encryption
for confidentiality are not new
The potential added value of our approach consists of:
The mechanisms to associate “Sticky” Privacy Policies to confidential data
via IBE (lightweight cryptography mechanism);
The “active” interaction model we introduced
The combined usage of TCG, Tagged OS and Trust Authorities for integrity
checking and policy enforcement
Other cryptography mechanisms could be used but the IBE model fits very well
at the client and server sites
Open issues:
Our policy enforcement is strong, but not impregnable (risks vs. costs?)
Adequacy of Trusted Platforms/Tagged OS to be verified
Potential complexity of our solution. To be fully prototyped and tested
Research in progress …
25/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

30. Current and Future Work
IBE technology is available. HP Labs have implemented a fast and optimised
version of the IBE cryptography libraries
We have simple implementations of:
- a TA service
- add-ins for authoring and management of privacy policies
- a policy-based engine
TPM chips and TCG-based PCs are available on the market
We have a working prototype of the Tagged OS
We have a working prototype of a non-repudiable, tamper resistant Auditing
and Logging System.
Next steps: testing the suitability of our approach in real contexts …
25/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

31. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Conclusions
It is important to protect people’s privacy on the Internet, increase
accountability and allow people to be more involved (if they care)
Despite laws, legislations and technical attempts to solve this problem,
at moment there are no solutions to address the whole set of involved issues
We described our approach to provide a strong but not impregnable
enforcement of privacy policies, more accountability and more user involvement
We presented a technical solution that leverages IBE (sticky policies and
auditing services), Tagged-OS (low level sticky policy) and TCG (trust
and integrity checking)
There are open issues: our research is in progress …
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

32. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Backup Slides
RSA and IBE
Cryptography Models
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

33. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
RSA Model
Secrets p&q
Compute d&e
Keep d secret
Compute N = p*q
encrypt
decrypt
N and d
e and N
published
Encrypted Msg
Msg
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

34. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
IBE Model [1]
Public
details E D
Encrypt
Decrypt
Secrets s
Compute public
Compute
Key pairs
Encrypted Msg
Msg
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

35. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
IBE Model [2]
Public
details
Encrypt
Decrypt
Secrets s
Compute public
Generate
Decryption Key
Encrypted Msg
Choose e
Get decrypt
Key,e
Msg
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK