Showing papers by "Chris J. Mitchell published in 1990"

Security defects in CCITT recommendation X.509: the directory authentication framework

Abstract: Security defects to be found in C.C.I.T.T. Recommendation X.509-1988 are described together with possible solutions.

Enumerating boolean functions of cryptographic significance

Abstract: In this paper we describe applications of functions from GF(2) m onto GF(2) n in the design of encryption algorithms. If such a function is to be useful it must satisfy a set of criteria, the actual definition of which depends on the type of encryption technique involved. This in turn means that it is important to ensure that the selected criteria do not restrict the choice of function too severely, i.e., the set of functions must be enumerated. We discuss some of the possible sets of criteria and then give partial results on the corresponding enumeration problems. Many open problems remain, some of them corresponding to well-known hard enumeration questions.

Key-minimal cryptosystems for unconditional secrecy

Abstract: This paper is concerned with cryptosystems offering perfect or unconditional secrecy. For those perfect-secrecy systems which involve using keys just once, the theory is well established; however, this is not the case for those systems which involve using a key several times. This paper takes a rigorous approach to the definition of such systems, and exhibits some new families of examples of systems providing perfect secrecy for which the number of keys is minimal.

Key-Minimal Cryptosystems for Unconditional Secrecy I

Abstract: This paper is concerned with cryptosystems offering perfect or un- conditional secrecy. For those perfect-secrecy systems which involve using keys just once, the theory is well established; however, this is not the case for those systems which involve using a key several times. This paper takes a rigorous approach to the definition of such systems, and exhibits some new families of examples of systems providing perfect secrecy for which the number of keys is minimal.

Infinite families of quasiperfect and doubly quasiperfect binary arrays

Abstract: A quasiperfect (doubly quasiperfect) binary array B is an s*t array with all entries plus or minus one, such that all periodic autocorrelation coefficients of the array are zero, except for shifts (u,v) where u identical to 0 mod s and v identical to 0 mod t. The authors construct a new infinite families of quasiperfect and of doubly quasiperfect binary arrays.

Key minimal authentication system for unconditional secrecy

Abstract: This paper is concerned with cryptosystems offering unconditional secrecy. For those perfect secrecy systems which involve using key just once, the theory is well established since Shannon’s works; however, this is not the case for those systems which involve using a key several times. This paper intends to take a rigorous approach to the definition of such systems. We use the basic model for a security code developped by Simmons, initially for unconditional authentication. We consider the definition of perfect L-fold secrecy given by Stinson and used by De Soete and others. We consider other definitions: Ordered Perfect L-fold secrety and Massey’s Perfect L-fold secrecy, and attempt to classify them. Lower bounds are given for the number of keys in such perfect systems, and characterisation of systems meeting these lower bounds are obtained. The last part of the paper is concerned with discussing examples of key minimal systems providing unconditional secrecy.