On the security of a modified Beth identity-based identification scheme

• We review Crescenzoʼs modified Beth-IBI scheme, Beth-IBI-1.
• We present an attack on Beth-IBI-1 that reveals the master secret key.
• We provide a short discussion on how and why the attack works.

In their seminal work for identity-based identification (IBI) schemes in 2004, Bellare et al. left open the question of whether the Beth identification scheme, and consequently the derived IBI scheme, can be proven secure against active and concurrent attackers. In 2008, Crescenzo answered the question in the positive by presenting a modified version of the Beth identification scheme as well as the corresponding derived IBI scheme. In this paper, we show that while the modified version of the Beth identification scheme proposed by Crescenzo is secure, an attack exists on the corresponding Beth-IBI scheme.