A Multi-use CCA-Secure Proxy Re-encryption Scheme

Proxy re-encryption (PRE) can be classified as single-hop PRE and multi-use PRE according to the times which the ciphertext is transformed. Finding a unidirectional, multi-use, and chosen ciphertext attack (CCA) secure PRE is presented as an open problem by Canetti et al. Wang claimed to resolve this problem by proposing the first multi-use CCA-secure unidirectional PRE scheme. But we found that different with single-hop PRE, multi-use PRE without randomize encrypt key in its re-encryption algorithm could be vulnerable to attack. A new type attack to multi-use CCA-secure PRE named proxy bypass attack is proposed with a concrete attacks on Wang-Multi-Use-PRE scheme. This attack is also effective for other multi-use scheme. At last we propose an improvement for Multi-Use-PRE to resist proxy bypass attack by randomize re-encryption algorithm.