IACR News item: 20 December 2015
Hui Guo, Zhenfeng Zhang, Jing Xu
ePrint Report
Proxy re-encryption (PRE) allows a semi-trusted proxy to transform a ciphertext for Alice into a ciphertext of the same message for Bob. The traditional security notion of PRE focuses on preventing the proxy with the re-encryption key learning anything about the encrypted messages. However, such a basic security requirement is clearly not enough for many scenarios where the proxy can collude with Bob. A desirable security goal is therefore to prevent a malicious proxy colluding with Bob to re-delegate Alices decryption right. In 2005, Ateniese, Fu, Green and Hohenberger first proposed this intriguing problem called non-transferability, in the sense that the only way for Bob to transfer Alices decryption capability is to expose his own secret key. It captures the notion that Bob cannot collude with the proxy and transfer Alices decryption right without compromising his own decryption capability. However, over the last decade, no solutions have achieved this property.
In this paper, we positively resolve this open problem. In particular, we give the first construction of nontransferable proxy re-encryption where the attacker is allowed to obtain one pair of keys consisting of Bobs secret key and the corresponding re-encryption key. Using indistinguishability obfuscation and k-unforgeable authentication as main tools, our scheme is provably secure in the standard model. The essential idea behind our approach is to allow Bobs secret key to be evoked in the process of decrypting Alices ciphertext while hiding the fact that only Bob could decrypt it by the obfuscated program. In addition, we also show a negative result: a CPA secure proxy re-encryption scheme with error-freeness property cannot be non-transferable.
In this paper, we positively resolve this open problem. In particular, we give the first construction of nontransferable proxy re-encryption where the attacker is allowed to obtain one pair of keys consisting of Bobs secret key and the corresponding re-encryption key. Using indistinguishability obfuscation and k-unforgeable authentication as main tools, our scheme is provably secure in the standard model. The essential idea behind our approach is to allow Bobs secret key to be evoked in the process of decrypting Alices ciphertext while hiding the fact that only Bob could decrypt it by the obfuscated program. In addition, we also show a negative result: a CPA secure proxy re-encryption scheme with error-freeness property cannot be non-transferable.
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