The ElGamal cryptosystem is the most widely used public key cryptosystem. It uses the discrete logarithm problem as the cryptographic primitive. The MOR cryptosystem is a similar cryptosystem. It uses the discrete logarithm problem in the automorphism group as the cryptographic primitive. In this paper, we study the MOR cryptosystem for finite p-groups. The study is complete for p-automorphisms...

More than 70 years ago, P. Hall showed that if G is a finite p -group such that a term G(d+1) of the derived series is non-trivial, then the order of the quotient G(d)/G(d+1) is at least p2 +1 . Recently Mann proved that, in a finite p -group, Hall’s lower bound can be taken for at most two distinct d . For odd p , we prove a sharp version of this result and characterise the groups with two sma...

We construct two classes of Gray maps, called type-I Gray map and type-II Gray map, for a finite p-group G. Type-I Gray maps are constructed based on the existence of a Gray map for a maximal subgroup H of G. When G is a semidirect product of two finite p-groups H and K, both H and K admit Gray maps and the corresponding homomorphism ψ : H −→ Aut(K) is compatible with the Gray map of K in a sen...

It would be interesting to extend this result by allowing B to have nilpotence class 2 instead of necessarily being abelian. This cannot be done if p = 2 (Example 4.2), but perhaps it is possible for p odd. (It was done by the author ([Gor, p.274]; [HB, III, p.21]) for the special case in which p is odd and [B,B] ≤ A.) However, there is an application of Thompson’s Replacement Theorem that can ...

Several properties of the products of finite maximal prefix, maximal biprefix, semaphore, synchronous, maximal infix and maximal outfix codes are discussed respectively. We show that, for two nonempty subsets X and Y of A such that the product XY being thin, if XY is a maximal biprefix code, then X and Y are maximal biprefix codes. Also, it is shown that, for two finite nonempty subsets X and Y...