Peter R. Wild
Cryptanalysis of a homomorphic public-key cryptosystem over a finite group
The paper cryptanalyses a public-key cryptosystem recently proposed by Grigoriev and Ponomarenko, which encrypts an element from a fixed finite group defined in terms of generators and relations to produce a ciphertext from SL(2, Z). The paper presents a heuristic method for recovering the secret key from the public key, and so this cryptosystem should not be used in practice.
Distributing the Encryption and Decryption of a Block Cipher
In threshold cryptography the goal is to distribute the computation of basic cryptographic primitives across a number of nodes in order to relax trust assumptions on individual nodes, as well as to introduce a level of fault-tolerance against node compromise. Most threshold cryptography has previously looked at the distribution of public key primitives, particularly threshold signatures and threshold decryption mechanisms. In this paper we look at the application of threshold cryptography to symmetric primitives, and in particular the encryption or decryption of a symmetric key block cipher. We comment on some previous work in this area and then propose a model for shared encryption / decryption of a block cipher. We will present several approaches to enable such systems and will compare them.