1. The HP Time Vault Service: Exploiting IBE for Timed Release of Confidential Information
Marco Casassa Mont
Keith Harrison
Martin Sadler
Trusted Systems Laboratory
Hewlett-Packard Labs, Bristol, UK
WWW 2003, May 2003
Budapest, Hungary

2. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Presentation Outline
Addressed Problem: Timed Release of Confidential Data
Scenarios
Requirements
Related Work
Our IBE-based Approach
Discussion
Conclusions
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

3. Problem: Timed Release of Confidential Data [1]
How to Protect Confidential Information
Until a Predefined Disclosure Time and
Deal With its Subsequent Disclosure?
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

4. Problem: Timed Release of Confidential Data [2]
It is a Common Real-life Problem:
Enterprise and Business Environment: confidential data can be disclosed to employee and stakeholders only at well defined point on time
B2B and E-Commerce: blind auctions, marketplaces, etc. The involved parties are prevented from accessing sensitive information for a predefined period of time
Ordinary Life: political elections, students’ exam results, etc.
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

5. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Scenarios [1]
Generation of
Confidential Data +
Disclosure Time
time
Starting to Protect
Disclosure &
Distribution
Confidential Data
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

6. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Scenarios [2]
Generation of
Confidential Data +
Disclosure Time
time
Distribution
Disclosure
Starting to Protect
Confidential Data
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

7. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Requirements
Solutions Dealing With This Problem Should:
Strongly Enforce Disclosure Constraints to Preserve Confidentiality
Avoid Bottlenecks
Be Simple
Be Provided by Accountable Organisations
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

8. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [1]
Time-Lock Puzzles:
Based on Computational Complexity
Intensive Usage of Computational Resources
Interesting Approach, but Unpractical
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

9. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [2]
Timed Release Cryptography [Approach 1]:
Uses Trusted Agents (i.e. Trusted Third Parties)
Confidential Data Encrypted and Stored Locally Until its Disclosure Time
Costs in Terms of Resources
Escrow Problem
Trusted Agent
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

10. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [3]
Timed Release Cryptography [Approach 2]:
Uses Trusted Agents
No Local Storage of Confidential Data
Publication of “Decryption” Secret at the Disclosure Time
Users Must Interact with the Trust Agent for Data Encryption
Trusted Agent
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

11. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Related Work [4]
Alternative Solutions Based on:
Encryption of Data based on Traditional
(RSA) Cryptography
Access Control
Hybrid Models
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

12. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Our Approach
Based on:
“Timed Release” Principles
Identifier-based Encryption (IBE)
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

13. 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 …
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

14. 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, Terms and Conditions, an Address, a Picture, a Disclosure Time
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
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

15. 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
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

16. Leveraging IBE for Timed Release of Confidential Information
Using “Disclosure Times” as IBE Encryption Keys, for example “GMT ”
IBE Decryption Keys are Generated by the Trust Authority
only at the Disclosure Time. No need to Store or Secure Them.
The Trust Authority Continuously Generates and Publishes IBE Decryption Keys corresponding to the Current Time, with a Predefined Frequency
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

17. The HP Time Vault Service: Model
The owner of confidential information encrypts it with an IBE encryption key – i.e. disclosure time of the document, for example “GMT ”, and then distributes it (No Interactions Required with the Time Vault Service!)
The receiver(s) has to wait until
the right time has come
before the IBE decryption key
is made available by the
Time Vault Service
Here the owner of confidential information uses a predictable encryption key knowing that the corresponding decryption key will only be available after a specific time
The Time Vault Service continuously generates and Publish IBE Decryption Keys, related to the current time, with a predefined frequency
Time=“GMT ”
Decryption Key = sdfsdfsdf32
Time Vault Service
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

18. The HP Time Vault Service: Architecture
IBE
Encryption
Module
Crypto Libraries
Decryption
GUI
Client Application/
Plug-in
Distribution Service
(on the Internet/Intranet)
WS APPS DB
Publishing
<Date Time,
IBE Decryption Key>
secret
IBE decryption
key Generator
Trusted
Time Server
(Trusted Authority) PD
Clock
IBE
Crypto Libraries
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

19. The HP Time Vault Service: Prototype [1]
Any Type
Of File
(.NET)
Application
Web Server
(IIS)
(.NET)
Web Service
(.NET) Application
date time
(Encryption
Key) PC
Clock
secret
GUI
IBE
Encryption
Module
IBE
Decryption
Module
IBE decryption
key generator
IBE
Decryption
key
<Date Time,
Decryption
Key>
IBE
Crypto Libraries
ASP
scripts
IBE
Crypto Libraries PD
.TLF file
(encrypted data +
metadata)
Pub. Key Dec. Key
SQL
Server
Client Application/
Plug-in
Distribution Service
Time Server
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

20. Comparison with a Solution based on Traditional Cryptography [1]
A Similar Service Can Be Build, Based on Traditional Public Key (RSA) Cryptography:
A Public key is Associated to the Time Server
Users Encrypt Confidential Information with a Symmetric Key
and Envelopes it along with the Time-based Disclosure Policies
(via the Time Server’s Public key)
On request, the Time Server Interprets the Disclosure
Polices: if satisfied issues the Symmetric key to the Requestor
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ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

21. Comparison with a Solution based on Traditional Cryptography [2]
Time Vault Service: Traditional RSA-based Approach
1. Define disclosure date (string)
2. Generate Symmetric Key Sk
3. Encrypt Document with Sk
4. Encrypt Sk with Time Server’s Public Key
5. Cluster the encrypted document with
the above metadata: got an extended document
8. Interpret Metadata: decide if disclosure time has come.
If it has, decrypt the encrypted symmetric key Sk
Public Key
Private Key
Sender
Access Points
Time Server
7. Send metadata
to Time Server
(through its Access Point)
6. Distribute your extended document
9. Return symmetric key
or an Error
10. Decrypt or
wait …
Receiver(s)
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

22. Comparison with a Solution based on Traditional Cryptography [3]
Time Vault Service: IBE-based Approach
*. (repeated) The Time Server
continuously generates and
publishes IBE decryption keys
associated to the current time
(IBE encryption key)
1. Generate Symmetric Key Sk
2. Encrypt Document with Sk
3. Encrypt Sk with disclosure date
i.e. IBE encryption key
4. Bundle the encrypted document with
the above metadata: get an
extended document
Distribution
Service
Public
Detail
Sender
Secret
6. Ask for IBE decryption key
associated to IBE encryption
key (stored in document’s metadata)
Time Server
5. Distribute the
extended document
7. Return decryption key
or an Error
8. Decrypt or
wait …
Receiver(s)
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

23. Comparison with a Solution based on Traditional Cryptography [2]
Our IBE-based approach:
Is Simpler To Run and More Modular
Potentially Simpler to Secure
More Efficient: The Time Server Has Not to Interpret
any Disclosure Policies during User Interactions
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

24. ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK
Conclusions
We addressed the Problem of Timed-release of Confidential Information
Current Solutions based on Timed-Release Cryptography Require Interactions
with a Trusted Agent at the Encryption Time
Solutions based on Traditional Cryptography Introduce Complexity
at the Time Server Side, during the Decryption Time
We described our IBE-based Solution: Simpler, more Modular and Efficient
The Feasibility of Our Approach demonstrated by a Working Prototype
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

25. 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

26. 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
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

27. 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
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

28. 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
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK

29. The HP Time Vault Service: Prototype [2]
date time
(Encryption
Key)
IBE
Decryption
key
<Date Time,
Decryption
Key>
Client Application/
Plug-in
Distribution Service
Time Server
20/04/2019
ﴀTrusted Systems Laboratory – Hewlett-Packard Labs, Bristol - UK