Band 12, Heft 3

In this paper, we construct some cartesian authentication codes from geometries over finite commutative rings. We only assume the uniform probability distribution over the set of encoding rules in order to be able to compute the probabilities of successful impersonation attack and substitution attack. Our methods are comfortable and secure for users, i.e., our encoding rules reduce the probabilities of successful impersonation attack and substitution attack.

In this paper, we consider a two party key-exchange protocol proposed in [D. Grigoriev and V. Shpilrain, Tropical cryptography , Comm. Algebra 43 (2014), 2624–2632, Section 2], which uses tropical matrix algebra as the platform. Our analysis shows that the scheme is not secure.

We show how to build a binary matrix from the MRHS representation of a symmetric-key cipher. The matrix contains the cipher represented as an equation system and can be used to assess a cipher’s resistance against algebraic attacks. We give an algorithm for solving the system and compute its complexity. The complexity is normally close to exhaustive search on the variables representing the user-selected key. Finally, we show that for some variants of LowMC, the joined MRHS matrix representation can be used to speed up regular encryption in addition to exhaustive key search.

Composite order pairing setting has been used to achieve cryptographic functionalities beyond what is attainable in prime order groups. However, such pairings are known to be significantly slower than their prime order counterparts. Thus emerged a new line of research – developing frameworks to convert cryptosystems from composite to prime order pairing setting. In this work, we analyse the intricacies of efficient prime order instantiation of cryptosystems that can be converted using existing frameworks. To compare the relative efficacy of these frameworks we mainly focus on some representative schemes: the Boneh–Goh–Nissim (BGN) homomorphic encryption scheme, ring and group signatures as well as a blind signature scheme. Our concrete analyses lead to several interesting observations. We show that even after a considerable amount of research, the projecting framework implicit in the very first work of Groth–Sahai still remains the best choice for instantiating the BGN cryptosystem. Protocols like the ring signature and group signature which use both projecting and cancelling setting in composite order can be most efficiently instantiated in the Freeman prime-order projecting only setting. In contrast, while the Freeman projecting setting is sufficient for the security reduction of the blind signature scheme, the simultaneous projecting and cancelling setting does provide some efficiency advantage.