This document summarizes a group signature scheme that is resistant to colluding attacks. It begins with definitions of group signatures and their requirements. It then discusses applications of group signatures, including e-voting, e-commerce, and corporate organizations. The document outlines the phases of a typical group signature scheme and the issue of collusion. It proposes a group signature scheme using a trusted third party to manage communications and prevent colluding attacks. The key phases of the proposed scheme are setup, join, signature generation, verification, and open. It discusses an implementation of the proposed scheme using Java and a database. In conclusion, the proposed scheme satisfies security properties and is applicable to applications like e-voting and e-commerce.

1. Presented by: Ravina jeswani Sophia Girls college(Autonomous) Ajmer.
M.Sc.(CS) Sem IV www.sophiacollegeajmer.in
Group signature scheme resistant
against
colluding attack
Presentation On

2. CONTENTS
•What is group signature ?
•Application of group signature
•Cryptography Concepts and Signature Requirements
•Classification of group signature schemes
•Phases of group signature scheme
•Collusion
•Group signature scheme resistant against colluding attack
•Implementation
•Conclusion

3. what is group signature ?
A digital signature is a mathematical scheme for providing the authenticity of a
digital information or document.
“A group signature scheme is a technique of signing the documents or any relevant
information anonymously on behalf of group, where group consist of manager and
various designated members”.
According to the Chaum and Heyst, the group signature must include following policies -
• Group members are only role person to sign the messages.
• The integrity of the signature should be checked without revealing the identity of the
signer.
• If necessary, the signature can be opened to reveal the identity of signer.

4. Cryptography Concepts and
Signature Requirements
Cryptography can be defined as protecting information by transforming into an unreadable
format, called cipher text. Only those who possess a secret key can decipher the message
into plain text. Encrypted messages can sometimes be broken by cryptanalysis, also called
code breaking, although modern cryptography techniques are virtually unbreakable.
Cryptography systems can be broadly classified into-
• symmetric-key systems
• Asymmetric-key systems

5. Applications of group signature
• Voting System : E-voting also known as electronic voting collectively means to cast
vote and count the votes electronically. E-voting is physically supervised by
representatives of governmental or independent electoral authorities where group
signature would be beneficial.
• Sales and Bidding System : E-commerce, is a type of industry where buying and selling
of product or service is conducted over electronic systems such as the Internet and other
computer networks. Group signature is effective and efficient way of providing security
in communicating within an organization.
• Corporate Organisation : Group signature proves to be efficient way to authorize the
information among everyone and saving the valuable time with a reliable approach.

6. Classification of group signature
• Static Group Signature : The static group signature determines all the parameters
initially with the group member in the group and also revocation is possible only
through removing of member but no addition of member allowed.
• Dynamic Group Signature : Random and non-deterministic nature of scheme.
• Group Signature with Verifiable Opening
• Group Signature with Distributed Roles

7. • System setup: includes key generation
mechanism.
• Join: includes joining of members in the group.
• Sign: performs the signature generation.
• Verify: verification of signature via group's
public key
• Open: the identity of signer can be revealed by
the group manager, if necessary.
Phases of group signature scheme

8. COllusion
Collusion as the name suggest is a act of cooperation between two person or set
of person for the sake of achieving mainly the illegal benefits.
Collusion is a very common and risky problem to be faced in every field which cannot be
controlled easily as the unpredictable nature of attack.
Scenario of collusion attack shown -

9. Group signature scheme resistant
against colluding attack
A trusted third party (TTP) is an entity involved in the proposed scheme who manages all
critical communications among the group members and group manager.
Proposed Scheme :
The proposed group signature scheme consists of four participants namely, group
manager, group members, designated verifier, and trusted third party. The scheme
consisting of following five phases -

10. • Setup phase-
• Join phase- QA. The trusted third party has database maintained for the member
according to the slot and structure defined.

11. • Signature generation phase- Key encrypted via manager's public key are finally
encrypted using group key and send to the verifier.
• Verification phase- The verifier gets the encrypted data which he decrypts using
the group key and verifier's private key accordingly.
• Open phase- The encrypted signature can be decrypted by manager with the
group key and can check the hash value that is encrypted with the manager's key.
As manager has the key hashed with respect to each member so can say who has
generated the signature.

12. implementation
The implementation of proposed scheme is done using Java platform and Mysql as
database for storing the key parameters.
The implementation consists of following steps in proposed scheme:
• Setup phase
• Join phase
• Signature generation phase
• Verify phase

13. • Setup phase-
• Join phase-

14. • Signature generation and Verification phase-

15. • The proposed scheme satisfies standard security features like anonymity, unforgeability,
and unlinkability.
• The proposed scheme is member independent such that any member leaving or
joining would not affect the signature generation scheme.
• The size of signature is still needed to be considered.
• The signers can be employees of the organization and the verifier may be a specific
customer.
• This scheme can also be applicable in e-voting system, e-cash system and e-commerce
applications.
Conclusion

16. Thank you