An Efficient Certificateless Proxy Re-Encryption Scheme without Pairing

Proxy re-encryption (PRE) is a cryptographic primitive introduced by Blaze, Bleumer and Strauss to provide delegation of decryption rights. PRE allows re-encryption of a ciphertext intended for Alice (delegator) to a ciphertext for Bob (delegatee) via a semi-honest proxy, who should not learn anything about the underlying message. In 2003, Al-Riyami and Patterson introduced the notion of certificateless public key cryptography which offers the advantage of identity-based cryptography without suffering from the key escrow problem. The existing certificateless PRE (CLPRE) schemes rely on costly bilinear pairing operations. In ACM ASIA-CCS SCC 2015, Srinivasan et al. proposed the first construction of a certificateless PRE scheme without resorting to pairing in the random oracle model. However, in this work, we demonstrate a flaw in the CCA-security proof of their scheme. Also, we present the first construction of a CLPRE scheme without pairing which meets CCA security under the computational Diffie-Hellman hardness assumption in the random oracle model

A Provably Secure Conditional Proxy Re-Encryption Scheme without Pairing

Blaze, Bleumer and Strauss introduced the notion of proxy re-encryption (PRE), which enables a semi-trusted proxy to transform ciphertexts under Alice\u27s public key into ciphertexts under Bob\u27s public key. The important property to note here is, the proxy should not learn anything about the plaintext encrypted. In 2009, Weng et al. introduced the concept of conditional proxy re-encryption (CPRE), which permits the proxy to re-encrypt only ciphertexts satisfying a condition specified by Alice into a ciphertext for Bob. CPRE enables fine-grained delegation of decryption rights useful in many practical scenarios, such as blockchain-enabled distributed cloud storage and encrypted email forwarding. Several CPRE schemes exist in the literature based on costly bilinear pairing operation in the random oracle model. We propose the first construction of an efficient CPRE scheme without pairing, satisfying chosen ciphertext security under the computational Diffie Hellman (CDH) assumption and its variant in the random oracle model

On the security of a Certificateless Proxy Re-Encryption Scheme without Pairing

Proxy re-encryption (PRE) is a cryptographic primitive introduced by Blaze, Bleumer and Strauss to provide delegation of decryption rights. A semi-trusted proxy agent re-encrypts ciphertexts under the public key of Alice into ciphertexts under the public key of Bob, without learning anything about the underlying message. In IWSEC 2017, Kuchta et al. presented a pairing-free certificateless proxy re-encryption scheme, and claimed that their scheme is the first to provide the certificateless property without resorting to pairing. They proved their construction is CCA-secure in the random oracle model, under the Computational Diffie-Hellman assumption. In this work, we show that the recently proposed construction of Kuchta et al. is vulnerable to several attacks

Sharing of Encrypted files in Blockchain Made Simpler

Recently, blockchain technology has attracted much attention of the research community in several domains requiring transparency of data accountability, due to the removal of intermediate trust assumptions from third parties. One such application is enabling file sharing in blockchain enabled distributed cloud storage. Proxy re-encryption is a cryptographic primitive that allows such file sharing by re-encrypting ciphertexts towards legitimate users via semi-trusted proxies, without them learning any information about the underlying message. To facilitate secure data sharing in the distributed cloud, it is essential to construct efficient proxy re-encryption protocols. In this paper, we introduce the notion of proxy self re-encryption (SE-PRE) that is highly efficient, as compared to the existing PRE schemes in the literature. We show that our self encryption scheme is provably CCA secure based on the DLP assumption and our proxy re-encryption scheme with self encryption is CCA secure under the hardness of the Computational Diffie Hellman (CDH) and Discrete Logarithm (DLP) assumption. Our novel encryption scheme, called self encryption, has no exponentiation or costly pairing operation. Even the re-encryption in SE-PRE does not have such operations and this facilitates the service provider with efficiency gain