Abstract. Certificateless public key cryptography (CLPKC) is a paradigm to solve the inherent key escrow problem suffered by identity-based cryptography (IBC). While certificateless signature is one of the most important security primitives in CLPKC, there are relatively few proposed schemes in the literature. In this paper, we manage to construct an efficient certificateless signature scheme based on the intractability of the computational Diffie-Hellman problem. By using a shorter public key, two pairing computations can be saved in the verification algorithm. Besides, no pairing computation is needed in the signing algorithm. The proposed scheme is existential unforgeable in the random oracle model. We also present an extended construction whose trust level is the same as that of a traditional signature scheme.
Abstract. In this paper, we first formalize the concept of ID-based identification scheme. Secondly, we show a transformation from any digital signature scheme satisfying certain condition to an ID-based identification scheme. As an instance, we present the first provably secure ID-based identification scheme based on the hardness of discrete logarithm problem. (More precisely, the hardness of gap Diffie-Hellman (GDH) problem.) We further show that for the ID-based signature scheme which is obtained by the Fiat-Shamir heuristic, a tight security bound is easily derived due to our transformation.
Abstract. In undeniable signature schemes, zero-knowledgeness and non-transferability have been identified so far. In this paper, by separating these two notions, we show the first 3-move confirmation and disavowal protocols for Chaum's undeniable signature scheme which is secure against active and concurrent attacks. Our main observation is that while the signer has one public key and one secret key, there exist two witnesses in the confirmation and disavowal proofs of Chaum's scheme.
Wang and Guo (Nonlinear Dyn 76(4): 1943-1950 proposed a new image alternate encryption algorithm based on chaotic map. The image alternate encryption can be conceptually treated as a block cipher where a round function which provides both confusion and diffusion is applied on a plain image iteratively. After performing the round function for T iterations, the processed image is denoted as the encrypted image. We analyse the security of Wang and Guo image encryption scheme, especially from cryptographic point of view, in line with the designers' approach in their security analyses. Negatively, we show that the image encryption scheme is vulnerable to an impossible differential attack (a type of chosen plaintext attack) and a divide-and-conquer attack when a large all black image is encrypted. This paper serves as another important security result showing that any future design of image encryption schemes based on chaotic map should be evaluated through systematic cryptanalytic approaches which include impossible differential attack. To the best of our knowledge, this is the first impossible differential attack applied on an image encryption algorithm.
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