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Establishment of Ad-Hoc Communities through Policy-Based Cryptography (Work in Progress)

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Title: Establishment of Ad-Hoc Communities through Policy-Based Cryptography (Work in Progress)


1
Establishment of Ad-Hoc Communitiesthrough
Policy-Based Cryptography(Work in Progress)
  • Walid Bagga , Stefano Crosta , Pietro Michiardi ,
    Refik Molva
  • bagga,crosta,michiardi,molva_at_eurecom.fr

2nd Workshop on Cryptography for Ad-Hoc Networks
(WCAN06), July 16th, 2006
2
Outline
  • Policy-Based Establishment of Ad-Hoc Communities
  • Ad-Hoc Communities
  • Current Approach
  • Policy-Based Encryption
  • Our Approach
  • Policy-Based Encryption from Bilinear Pairings
  • Policy Model
  • Formal Definition
  • Basic Concepts on Bilinear Pairings
  • Our Policy-Based Encryption Scheme
  • Summary and Future Work

3
Policy-Based Establishment of Ad-Hoc Communities
4
Ad-Hoc Communities
  • Definition An ad-hoc community interconnects a
    group of devices, maintains membership and
    ensures that only entities, i.e., users or
    computing services, which possess certain
    credentials, attribute information and
    characteristics can join the community (common
    characteristics). The members of the community
    rely upon each other to provide services and
    share resources (interactions). These
    interactions are regulated through a set of
    well-defined policies that govern the access to
    the services and resources in the community.
  • A security framework is needed to ensure
    trustworthy interactions within ad-hoc
    communities.

5
Current Approach Keoh et al., ACSAC04
  • Scenario Alice is on a business trip for the
    collaborative project P. On the train there might
    be other colleagues from different companies
    working on the same project. Alice has some
    documents she is willing to share and possibly
    discuss only with the members of the project that
    are either from company X or from company Y.
  • Bob wants to join Alices Community
  • Bob gives his credentials to Alice
  • Alice Checks the validity of the credentials
  • Alice Checks that the credential fulfill her
    Policy
  • Alice admits Bob as a member of her community

6
Policy-Based Encryption
Multiple Trusted Authorities
Policy
Credentials
1
2
3
Y
X
  • Idea Encrypt a message with respect to a policy
    so that only users fulfilling the policy are able
    to decrypt the message

7
Our Approach
  • Bob wants to join Alices Community
  • Advantages
  • Optimal number of interactions between Alice and
    Bob
  • Compliance with the privacy principle of Data
    Minimization OECD Guidelines

8
Policy-Based Encryption from Bilinear Pairings
9
Policy Model
  • A set of credential issuers
  • A policy consists of
  • conjunctions
  • disjunctions

of conditions
  • A condition is defined through
  • A credential issuer
  • An assertion

fulfilled by credential
  • A policy is written in standard normal form
  • Conjunctive Normal Form (CNF)
  • Disjunctive Normal Form (DNF)
  • A qualified set of credentials for is
    denoted

10
Formal Definition
  • A Policy-Based Encryption scheme (PBE) consists
    of 5 algorithms
  • Consistency constraint to be fulfilled

11
Basic Concepts on Bilinear Pairings
  • Bilinear Diffie-Hellman Parameters
  • Additive Group
  • Multiplicative Group
  • Generator
  • Bilinear Pairing
  • Bilinear
  • Non-Degenerate
  • Computable

same prime order
satisfying the following properties
12
Our PBE Scheme (1/3)
  • Setup Algorithms

13
Our PBE Scheme (2/3)
  • Encryption and Decryption Algorithms

14
Our PBE Scheme (3/3)
  • Performance
  • Provable Security for Policy-Based Encryption
  • Semantic Security against Chosen Ciphertext
    Attacks (IND-Pol-CCA)
  • Reductionist Security Proof

15
Summary and Future Work
  • Contributions
  • Novel Approach for Ad-Hoc Community Establishment
  • Concrete Policy-Based Encryption Scheme
  • Current and Future Work
  • Improve the performance of Policy-Based
    Encryption
  • Policy-Based Encryption v.s. Generalized
    Threshold Decryption
  • Design and Implementation of a Proof-of-Concept
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