Affiliation: Jinan University
CCA-Secure Unidirectional Proxy Re-Encryption in the Adaptive Corruption Model without Random Oracles
Proxy re-encryption (PRE), introduced by Blaze, Bleumer and Strauss in Eurocrypt'98, allows a semi-trusted proxy to convert a ciphertext originally intended for Alice into an encryption of the same message intended for Bob. PRE has recently drawn great interest, and many interesting PRE schemes have been proposed. However, up to now, it is still an important question to come up with a chosen-ciphertext secure unidirectional PRE in the adaptive corruption model. To address this problem, we propose a new unidirectional PRE scheme, and prove its chosen-ciphertext security in the adaptive corruption model without random oracles. Compared with the best known unidirectional PRE scheme proposed by Libert and Vergnaud in PKC'08, our schemes enjoys the advantages of both higher efficiency and stronger security.
On the Security of a Bidirectional Proxy Re-Encryption Scheme from PKC 2010
In PKC 2010, Matsuda, Nishimaki and Tanaka proposed a bidirectional proxy re-encryption (PRE) scheme without bilinear maps, and claimed that their scheme is chosen-ciphertext secure in the standard model. However, by giving a concrete attack, in this paper we indicate that their PRE scheme fails to achieve the chosen-ciphertext security. The purpose of this paper is to clarify the fact that, it is still an open problem to come up with a chosen-ciphertext secure PRE scheme without bilinear maps in the standard model.
CCA-Secure PRE Scheme without Public Verifiability
In a proxy re-encryption (PRE) scheme, a semi-trusted proxy can transform a ciphertext under Alice's public key into another ciphertext that Bob can decrypt. However, the proxy cannot access the plaintext. Due to its transformation property, PRE can be used in many applications, such as encrypted email forwarding. All the existing CCA-secure PRE schemes have a crucial property: the public verifiability of the original ciphertext, i.e., everyone can check the validity of the original ciphertext. In this paper, we propose a novel CCA-secure PRE scheme without public verifiability. This proposal is proven-secure based on the DDH assumption in the standard model. To the best of our knowledge, our proposal is the first CCA-secure unidirectional PRE scheme without pairings in the standard model, which answers an open problem in the PRE field.
Fast Digital Signature Schemes as Secure as Diffie-Hellman Assumptions
This paper presents two fast digital signature schemes based on Diffie-Hellman assumptions. In the random oracle model, the first scheme S1 has a tight security reduction to the computational Diffie-Hellman (CDH) problem; and the second scheme S2 has a tight security reduction to the decisional Diffie-Hellman (DDH) problem. Comparing with existing signature schemes (whose security is tightly related to CDH problem) like EDL signature schemes, the signature generation of S1 is about 27% faster, and the verification is about 35% faster, if without considering the hash function evaluations. Comparing with existing signature schemes (whose security is tightly related to DDH problem) like KW-DDH signature scheme, the signing of S2 is about 40% faster and the verification is about 35% faster. The high efficiency of the proposed schemes is attributed to a new protocol EDL_mwz which implements the proof of equality of discrete logarithm. The EDL_mwz protocol outperforms its counterpart, the Chaum and Pedersen protocol, as its computation is about 38% faster and its bandwidth is |G| bits shorter. This new protocol may be of independent interests.