Cryptology ePrint Archive: Report 2012/431

On the Security of Dynamic Group Signatures: Preventing Signature Hijacking

Yusuke Sakai and Jacob C.N. Schuldt and Keita Emura and Goichiro Hanaoka and Kazuo Ohta

Abstract: We identify a potential weakness in the standard security model for dynamic group signatures which appears to have been overlooked previously. More specifically, we highlight that even if a scheme provably meets the security requirements of the model, a malicious group member can potentially claim ownership of a group signature produced by an honest group member by forging a proof of ownership. This property leads to a number of vulnerabilities in scenarios in which dynamic group signatures are likely to be used. We furthermore show that the dynamic group signature scheme by Groth (ASIACRYPT 2007) does not provide protection against this type of malicious behavior.

To address this, we introduce the notion of \emph{opening soundness} for group signatures which essentially requires that it is infeasible to produce a proof of ownership of a valid group signature for any user except the original signer. We then show a relatively simple modification of the scheme by Groth which allows us to prove opening soundness for the modified scheme without introducing any additional assumptions.

We believe that opening soundness is an important and natural security requirement for group signatures, and hope that future schemes will adopt this type of security.

Category / Keywords: public-key cryptography / group signature

Publication Info: An extended abstract appears in The 15th International Conference on Practice and Theory in Public Key Cryptography (PKC 2012).

Date: received 30 Jul 2012

Contact author: yusuke sakai at uec ac jp

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Version: 20120805:145246 (All versions of this report)

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