Paper 2010/333

Cryptanalysis of Libert-Vergnaud Proxy Re-encryption Scheme

Zhengjun Cao

Abstract

In 2008, Libert and Vergnaud put forth a proxy re-encryption scheme (LV08 for short). Unlike some earlier PRE schemes, the LV08 scheme specifies a validity-checking process to guarantee that the received ciphertext is well-formed. In this paper, we clarify an ultimate fact that the received message is well-formed is the premise to decryption in all encryption schemes. The underlying mechanism to keep the communicated message well-formed in encryption schemes is another topic. The authors ignored the fact and proposed a cumbersome presentation. We will simplify the LV08 scheme and show its security level is the same as that of the scheme proposed by Ateniese et al in 2005. Therefore, the LV08 scheme can not ensure chosen-ciphertext security as claimed.