1. A Flexible Role-based Secure Messaging Service: Exploiting IBE Technology for Privacy in Health Care
Marco Casassa Mont
Pete Bramhall
Keith Harrison
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
Addressed Problems
Scenarios
Requirements
Related Work
Our Approach
Discussion
Conclusions
16/02/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

3. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Setting the Context
Organisations are more and more complex, dynamic and flexible: people’s roles, rights and duties can frequently
change
Confidential information needs to be protected whilst it is
exchanged and accessed, especially in dynamic environments
Messaging services (such as services), are commonly used to exchange information within and across organisations
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

4. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Addressed Problems
Enforcement of confidentiality and privacy of
information in dynamic contexts, where people’s roles
and permissions are subject to frequent changes
Allow the exchange of confidential information in a way
that only the entities that satisfy predefined privacy policies,
at a specific point in time, can access it
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

5. Context: UK Health Care Service
Focus on an Health Care Service:
example of dynamic organisation
Roles (GP, Doctor, Consultant,
Nurse, etc.) can be played by
different people at different time
We partnered with a UK
Health Care Organization
to understand real problems
and have a Technology Trial
of our solutions
Most of the employees use the
service but …
At moment interactions involving
confidential patient data are mainly
paper-based: need to be compliant
with Data Protection and Privacy
Laws …
Waiting List
Administration Teams
Referral
Letter
Referral
Letter
Assistant GP
Referral
Letter
Nurse
Consultant
Surgeries
Discharge
Letter
Departments
Hospitals
Health Service Network
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

6. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Scenarios [1]
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

7. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Scenarios [2]
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

8. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Our Goals
Automate the exchange of Confidential Information
by preserving the Privacy of Patients: i.e. only
the people with the right roles and permissions
will access it
Provide a Flexible, Role-based Secure
service
Learn from the Trial and investigate usages of
the adopted solution in other “dynamic contexts”
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

9. High-level Requirements
Requirements for a secure service (Health Care Trial):
Strong Authentication of the involved parties
Privacy and Confidentiality: obfuscation of confidential data
Policy-based Disclosures: privacy policies strictly associated to
confidential messages. It must be possible
to tell if they have been tampered with.
Flexibility: Privacy policies must be flexible. it must be possible to
specify role-based disclosure policies. Support for late
binding of roles. Users define their own disclosure policies.
Simplicity of Usage and Management
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

10. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [1]
Usage of traditional public key cryptography and digital certificates for confidentiality, non-repudiation and authentication purposes. Example of S/MIME, for services:
Alice’s
Private Key
Public Keys
(Certificates)
Bob’s
Private Key
service
Alice
Bob
Encryption
Plaintext
Ciphertext
Decryption
Plaintext
Bob’s
Public Key
Bob’s
Private Key
Does it address our problems? …
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

11. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [2]
If disclosure polices depend on the Identity of the receiver, the usage of digital certificates
and public key cryptography is viable. Confidential messages are encrypted
with the public key (within the digital certificate) of the receiver. Examples: S/MIME
If these policies do not (directly) depend on the identity but on other aspects, such as Roles
or terms and conditions, the above approach does not work!
At priori (at the encryption time) , the Identity of the Receivers might not be known! Case of
Late Binding of the Identity. This is the case we are addressing.
Receiver’s Identity
Known at the
sending time
Alice
Bob
Bob
Role X
Charles
Receiver’s Identity
Unknown at the
sending time
Alice …
Late Binding
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

12. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [3]
Introducing a further level of indirection via a “third party”:
It must be trusted
Encryption/decryption of messages (along with the associated disclosure polices)
by using its keys
Usage of enveloping techniques (PKCS#7, etc.)
It can be coupled with Role-based Access Control mechanisms (RBAC)
 It can be implemented by using public key/PKI technologies
Cons: - It is not the most natural way of using public key/PKI for services (e.g. S/MIME)
- Complexity of PKI-based solutions for end-users
Alice
Bob
Charles …
Trusted Mediator
RBAC
Bob has
Role x
Mediator’s
Public Key
Encrypted data
+ policies x
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

13. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Our Approach
Based on:
Identifier-based Encryption (IBE) technology
Reasons:
Explore alternative/complementary solutions
Investigate the suitability of IBE technology
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

14. 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

15. 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

16. 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

17. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Our Solution [1]
Based on the IBE Model: reliance on Trust Authority(ies)
Privacy policies are represented as IBE encryption keys:
Generated by the sender of confidential messages
Contain list of roles to be played by the intended receivers
Example: “Member of The Waiting List Team”
If tampered with, the associated cannot be decrypted
Trust Authority (TA):
Checks for policy compliance
Generates, on-the-fly, IBE decryption keys
Policy compliance check:
Authentication of the requestor to the TA
The requestor must have the roles defined by the IBE encryption key at the
request time
List of people’s current roles managed by the TA
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

18. Encrypted confidential data Generation and issuance of
Our Solution [2] 1
Encrypted confidential data
+ IBE Encryption Key
(Required Roles)
service
Sender
Receiver 2
Request for
IBE Decryption Key 3
Generation and issuance of
IBE Decryption Key,
If the receiver has the
required roles
Trust
Authority
Tables
Roles
<Identity, Roles> Mappings
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

19. Additional Technical Constraints
Technical constraints dictated by the trial environment:
Authentication of Health Care’s employees via Microsoft Authentication (NT Logon).
Unique login account for each employee. Policies dictate its correct usage
MS Windows Trust Domains associated to Health Care Entities (Surgeries, Hospitals, etc)
for “authentication management” purposes
Usage of Microsoft Outlook 2000 at the client site (GPs, Nurses, Consultants, etc.) as
browser
Exchange of confidential information within the Health Care Organisation’s Intranet
Hospital
Trust Domain GP
Health Care Organisation - Intranet
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

20. High-level System Architecture
Browser Add-in:
- Standard MS Outlook 2000add-in,
containing IBE encryption/decryption
libraries
- Secure connection (https) and
authentication to the TA
- XML-based encryption envelopes
Trust Authority (TA):
secure web service, with IBE key
generation libraries. Protection
of TA secret in secure vault. Run in a
stand-alone TA trust domain by
trusted administrators, in a secure site
Database:
simple MS SQL Server database at
the TA site containing list of
current roles and up-to-date mappings of
users’ identities (NT logon) to their roles
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

21. System Architecture: Information Flow
MS Outlook 2000
MS Outlook 2000
service
IBE Add-in
IBE Add-in 1
Encrypted
Request for
IBE Decryption Key by
sending (part of) the
XML Wrapper
(via https channel)
Sender
+ XML Wrapper
(containing encrypted
IBE Encryption Key)
Receiver 2 3
Generation and Issuance of
IBE Decryption Key,
If privacy policies are satisfied
(via https channel)
IIS
IIS
.ASP
ASP
Trust Authority
Trust
Authority
Trust
Authority
Engine
TA Secret
Secure
Vault
Tables
Roles
<Identity, Roles>
Mappings
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

22. Encrypted e-Mail: XML Wrapper Details
<?xml version="1.0" ?>
- <IB Ciphertext>
<EphemeralKey> </EphemeralKey>
<IBEPublicKeyCiphertextLength>280</IBEPublicKeyCiphertextLength>
<IBEPublicKeyCiphertext>
3affcffdc1ea36455fcf rt4rg5uyhg6u
</IBEPublicKeyCiphertext>
<IB BodyCiphertextLength>
1384
</IB BodyCiphertextLength>
<IB BodyCiphertext>
d53f07f88946e6411db83f4daeb72bdb c2b900
</IB BodyCiphertext>
<UID> </UID>
<TimeSent>03:14:31 PM, Monday, Mar </TimeSent>
</IB Ciphertext>
(Random) Ephemeral Key
To encrypt Disclosure Policy
Encrypted Disclosure Policy
Exposed to TA (no
content is ever exposed
to TA)
Encrypted Body
( attachments are
encrypted and attached)
Information for Receipting
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

23. E-mail Browser Add-in: Snapshots
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

24. Addressing the Requirements
Authentication`
Reliance on Windows Authentication (out of our scope in the trial). Introduced a TA trust domain that trusts the existing trust domains
Privacy and
Confidentiality
Encryption of Confidential by using IBE
Policy based
Disclosure
Disclosure policies expressed via IBE Encryption Keys, specifying the roles to be played by the intended receivers. The TA interprets and checks for their compliance. Control given to the senders of confidential information.
Flexibility
Flexibility in defining disclosure policies: they can be extended to include more complex terms and conditions. Support for late binding of roles. Usage of multiple TAs if required.
Simplicity
Users: Intuitive, integrated solution with browser
Administrator: database tables to be kept up-to-date (similar issues to RBAC)
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

25. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Discussion
Our solution is a practical application of IBE cryptography deployed in a real
context (related work: IBE-based service by Stanford University)
We leveraged IBE for encryption purposes. It was straightforward
to do it, in a close and trusted environment. Need to explore the
implications in an open, untrusted environment …
Heavy reliance on a “third party” authentication mechanism …
We are exploring IBE-based authentication mechanisms. We do not have
practical evidence that they are better or more usable than traditional (PKI)
solution.
In general we believe IBE is a complementary technology to
public key cryptography/PKI …
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

26. Current and Future Work
We have an optimised version of IBE cryptography libraries
(performance of cryptographic operations comparable to RSA).
We are exploring how to extend our solution to include:
multiple IBE Trust Authorities (for key-escrow and trust reasons)
more complex disclosure policies
16/02/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

27. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Conclusions
Privacy management is a major problem for modern, dynamic
organisations
Important issue: preserve data confidentiality when exchanged
via
Current limitations and complexity of PKI-based solutions
We partnered with a Health Care Organisation.
Goal: provision of a flexible, role-based secure service
Our approach: leveraging IBE technology to enforce
privacy, in a flexible, simple and secure way
We have built a solution that is used in a Trial.
IBE is a viable technology for encryption purposes
The Trial is ongoing and our research is in progress …
16/02/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

28. 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

29. 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

30. 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

31. 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