In 1998, Blaze, Bleumer and Strauss introduced a cryptographic primitive called proxy re-encryption in which a proxy can transform-without seeing the plaintext-a ciphertext encrypted under one key into an encryption of the same plaintext under another key. The concept has recently drawn renewed interest. Notably, Canetti and Hohenberger showed how to properly define (and realize) chosen-ciphertext security for the primitive. Their system is bidirectional as the translation key allows converting ciphertexts in both directions. This paper presents the first unidirectional proxy re-encryption schemes with chosen-ciphertext security in the standard model (i.e., without the random oracle idealization). The first system provably fits a unidirectional extension of the Canetti-Hohenberger security model. As a second contribution, the paper considers a more realistic adversarial model where attackers may choose dishonest users' keys on their own. It is shown how to modify the first scheme to achieve security in the latter scenario. At a moderate expense, the resulting system provides additional useful properties such as non-interactive temporary delegations. Both constructions are efficient and rely on mild complexity assumptions in bilinear groups. Like the Canetti-Hohenberger scheme, they meet a relaxed flavor of chosen-ciphertext security introduced by Canetti, Krawczyk and Nielsen.
In 1998, Blaze, Bleumer and Strauss introduced a cryptographic primitive called proxy re-encryption in which a proxy can transform-without seeing the plaintext-a ciphertext encrypted under one key into an encryption of the same plaintext under another key. The concept has recently drawn renewed interest. Notably, Canetti and Hohenberger showed how to properly define (and realize) chosen-ciphertext security for the primitive. Their system is bidirectional as the translation key allows converting ciphertexts in both directions. This paper presents the first unidirectional proxy re-encryption schemes with chosen-ciphertext security in the standard model (i.e., without the random oracle idealization). The first system provably fits a unidirectional extension of the Canetti-Hohenberger security model. As a second contribution, the paper considers a more realistic adversarial model where attackers may choose dishonest users' keys on their own. It is shown how to modify the first scheme to achieve security in the latter scenario. At a moderate expense, the resulting system provides additional useful properties such as non-interactive temporary delegations. Both constructions are efficient and rely on mild complexity assumptions in bilinear groups. Like the Canetti-Hohenberger scheme, they meet a relaxed flavor of chosen-ciphertext security introduced by Canetti, Krawczyk and Nielsen.
Blaze et al. in 1998 introduced the concept of proxy re-encryption, which allows a proxy to transform a ciphertext computed under Alice's public key into one that can be opened under Bob's decryption key. In CCS'07, Canetti et al. proposed an IND-PRE-CCA2 bidirectional proxy re-encryption scheme, and later, Libert et al. proposed another IND-PRE-CCA2 secure unidirectional proxy re-encryption. However, both schemes rely on the costly bilinear pairings. In CANS'08, Deng et al. proposed the first IND-PRE-CCA2 secure proxy re-encryption without parings. Later, in PKC'09, Shao et al. proposed another IND-PRE-CCA2 secure proxy re-encryption without parings. But both of these schemes prove their security in the random oracle. In this paper, based on Hanaoka's efficient chosen ciphertext secure public key encryption under the computational Diffie-Hellman assumption, we present two new interesting bidirectional proxy re-encryption schemes, which are restricted IND-PRE-CCA2 secure without pairing nor random oracle.
A proxy re-encryption (PRE) scheme allows a designated proxy, that has beforehand received aso-called re-encryption key, to translate a ciphertext intended to one user to a ciphertext intendedto another one. Traditionally, the re-encryption key is generated at the initiative of the initialreceiver and ideally, no secret keys should be known to the proxy. Such scheme is said unidirectionalif the transformation from one user to another does not necessarily imply the possibility tomake the inverse transformation. Regarding the literature on unidirectional proxy re-encryption, itseems hard to prove the strongest security level (namely indistinguishability under chosen ciphertextattacks - IND-CCA) of such schemes. Most of the time, PRE either reaches a chosen-plaintextsecurity or a replayable CCA security. At Africacrypt 2010, Chow, Weng, Yang and Deng proposeda scheme that satisfies CCA security in the random oracle model. However, their modelcan actually be strengthen. Indeed, we show in this paper how to modify this scheme so that itsimproved security achieves a full CCA security. In particular, we now allow the adversary of theCCA security for re-encryption to corrupt the user i′ who is the initial receiver of the challengedciphertext and at the same time to obtain the re-encryption key from i′ to the targeted users. Theresulting scheme is therefore a fully secure PRE which does not rely on pairings, and secure in therandom oracle model. It can be implemented efficiently with any traditional modular arithmetic.
Proxy re-encryption, introduced by Blaze et al. in 1998, allows a proxy to transform a ciphertext computed under Alice's public key into one that can be opened under Bob's decryption key. An open problem of constructing (bidirectional or unidirectional) IND-PRE-CCA2 secure proxy re-encryption scheme in the standard model yet without pairings was left until now. In this paper, based on Hanaoka's efficient chosen ciphertext secure public key encryption under the computational Diffie-Hellman assumption, we try to solve this open problem by presenting two new bidirectional proxy re-encryption schemes, which are restricted IND-PRE-CCA2 secure without pairing nor random oracle.
Libert and Vergnaud proposed a unidirectional proxy re-encryption scheme with temporary delegation (IEEE Trans. Inf. Theory, vol. 57, no. 3, pp. 1786–1802, Mar. 2011). They claimed that the scheme is chosen ciphertext secure in the chosen key model. However, their proof has a minor error in the simulation of the re-encryption oracle. The adversary is able to distinguish between the simulated environment and the real attack environment by using responses from the re-encryption oracle. Fortunately, we can amend the proof without any modification of the original scheme.
In an identity-based proxy re-encryption scheme, a semi-trusted proxy can convert a ciphertext under Alice's public identity into a ciphertext for Bob.The proxy does not know the secret key of Alice or Bob, and also does not know the plaintext during the conversion.In identity-based proxy re-encryption, the collusion of the proxy and a delegatee may result in the decryption of ciphertext for delegator.In this paper, we present a new scheme which can avoid the collusion of proxy and delegatee.Our scheme improves the scheme of Chu and Tzeng while inheriting all useful properties such as unidirectionality and non-interactivity.In our scheme, we get the security by using added secret parameter and change the secret key and re-encryption key.Our sheme is secure against Chosen-Ciphertext Attack (CCA) and collusion attack in the standard model.
In this work, we study (the direct constructions of) bidirectional proxy re-encryption (PRE) with alleviated trust in the proxy, specifically the master secret security (MSS) and the nontransitivity (NT) security, in the standard model, and achieve the following: • A multi-hop MSS-secure bidirectional PRE scheme with security against chosen plaintext attacks (CPA) in the standard model, where the ciphertext remains constant size regardless how many times it has been re-encrypted. To the best of our knowledge, there exists previously no MSS-secure multi-hop bidirectional PRE scheme with constant size of ciphertexts (whether in the random oracle model or not). • A single-hop MSS-secure and non-transitive bidirectional PRE scheme with security against chosen ciphertext attacks (CCA) in the standard model. The CCA-secure scheme is based on the CPA-secure scheme, and particularly employs a new re-encryption key (REK) generation mechanism to which each user makes equal contributions, where a single REK is used in both directions with the same computation so that the proxy needs not to distinguish the transform direction when it re-encrypts ciphertexts. Besides alleviated trust in proxy, single-hop non-transitive bidirectional PRE schemes also enjoy better fine-grained delegate right control (against malicious proxy). The security analysis uses Coron’s technique [Coron, Crypto 2000], which particularly allows adaptive secret-key corruption. Along the way, we also refine and clarify the security models for bidirectional PRE. 1