Choi et al. proposed the modified Paillier cryptosystem (M-Paillier cryptosystem). They use a special public-key g ∈ ZZ/nZZ such that gφ(n) = 1 + n mod n2, where n is the RSA modulus. The distribution of the public key g is different from that of the original one. In this paper, we study the security of the usage of the public key. Firstly, we prove that the one-wayness of the M-Paillier crypto...

The classical certificate systems are computationally inefficient, since they use signature operations based on public key cryptosystems. The nested certificates (A. Levi, Design and performance evaluation of the nested certification scheme and its applications in public key infrastructures, Ph.D. Thesis, Department of Computer Engineering, Boğaziçi University, Istanbul, Turkey) are proposed to...

In 1991, Damgård proposed a simple public-key cryptosystem that he proved CCA1-secure under the Diffie-Hellman Knowledge assumption. Only in 2006, Gjøsteen proved its CCA1-security under a more standard but still new and strong assumption. The known CCA2-secure public-key cryptosystems are considerably more complicated. We propose a hybrid variant of Damgård’s public-key cryptosystem and show t...

We demonstrate that the public key cryptosystems using the modular group suggested in [4,5] are vulnerable to very simple ciphertextonly attacks. Consequently, in the present form both of these systems cannot be considered as sufficiently secure for cryptographic purposes.

We show that if the private exponent d used in the RSA public-key cryptosystem is less than N then the system is insecure. This is the first improvement over an old result of Wiener showing that when d < N the RSA system is insecure. We hope our approach can be used to eventually improve the bound to d < N.

Public-key cryptosystems are suggested based on invariants of groups. We give also an overview of known cryptosystems which involve groups.

In this paper, we present a new method for sharing images between two parties exploiting homomorphic property of public key cryptosystem. With our method, we show that it is possible to multiply two encrypted images, to decrypt the resulted image and after to extract and reconstruct one of the two original images if the second original image is available. Indeed, extraction and reconstruction o...

In this paper we describe a cryptanalysis of MST 3, a public key cryptosystem based on non-commutative groups recently proposed by Lempken, Magliveras, van Trung and Wei.

A public key infrastructure (PKI) is for facilitating the authentication and distribution of public keys. Currently, the most commonly employed approach to PKI is to rely on certificate authorities (CAs), but recently there has been arising more need for decentralized peer-to-peer certification like Webs of Trust. In this paper, we propose an identity-embedding method suitable for decentralized...

Throughout the history of cryptography, hundreds of cryptosystems have been developed. The earliest ones, as well as many later ones, relied on the complete secrecy in transferring keys between the sender and recipient. These kinds of systems, called secret key cryptosystem, have just a single key which is used for both encryption and decryption; therefore, these systems are more frequently kno...