We explore whether non-malleability is necessary for the applications typically used to mo-tivate it, and propose two alternatives. The first we call weak non-malleability (wnm) and showthat it suffices to achieve secure contract bidding (the application for which non-malleability wasinitially introduced), despite being strictly weaker than non-malleability. The second we callta...

A presentation of a group with two generators having unsolvable word problem and an explicit countable presentation of Mihailova subgroup of F2 × F2 with finite number of generators are given. Where Mihailova subgroup of F2 × F2 enjoys the unsolvable subgroup membership problem. One then can use the presentation to create entities’ private keys in a public key cryptsystem.

Constructing identity based schemes is one of the hot topics of current cryptography. Hierarchical identity based cryptography is a generalization of identity based encryption that mirrors an organizational hierarchy. It allows a root public key generator to distribute the workload by delegating public key generation and identity authentication to lower-level public key generators. Currently, t...

Rainbow is a fast asymmetric multivariate signature algorithm proposed by J. Ding and D. Schmidt in [5]. This paper presents a cryptanalysis of Rainbow which enables an attacker provided with the public key to recover an equivalent representation of the secret key, thus allowing her to efficiently forge a signature of any message. For the set of parameter values recommended by the authors of Ra...

Key establishment in sensor networks is a challenging problem because asymmetric key cryptosystems are unsuitable for use in resource constrained sensor nodes, and also because the nodes could be physically compromised by an adversary. We present three new mechanisms for key establishment using the framework of pre-distributing a random set of keys to each node. First, in the q-composite keys s...

After making the decision to use public-key cryptography, an organisation still has to make many important decisions before a practical system can be implemented. One of the more difficult challenges is to decide the length of the keys which are to be used within the system: longer keys provide more security but mean that the cryptographic operation will take more time to complete. The most com...

Csiszàr and Narayan[3] show that the secret-key capacity CSK(A) with unlimited public discussion and the smallest achievable rate RCO(A) of communication for omniscience of a group A of at least two active users sum up to the entropy rate H(XM) of the discrete multiple memoryless sources (Xi, i ∈ M) for all terminals M ⊃ A. They then derive a heuristically appealing upperbound[3, (26)] on the s...