Showing papers on "Block cipher published in 1989"

On the Construction of Block Ciphers Provably Secure and Not Relying on Any Unproved Hypotheses

Abstract: One of the ultimate goals of cryptography researchers is to construct a (secrete-key) block cipher which has the following ideal properties: (1) The cipher is provably secure, (2) Security of the cipher does not depend on any unproved hypotheses, (3) The cipher can be easily implemented with current technology, and (4) All design criteria for the cipher are made public. It is currently unclear whether or not there really exists such an ideal block cipher. So to meet the requirements of practical applications, the best thing we can do is to construct a block cipher such thai it approximates the ideal one as closely as possible. In this paper, we make a significant step in this direction. In particular, we construct several block ciphers each of which has the above mentioned properties (2), (3) and (4) as well as the following one: (1’) Security of the cipher is supported by convincing evidence. Our construction builds upon profound mathematical bases for information security recently established in a series of excellent papers.

Methodologies for designing block ciphers and cryptographic protocols

Abstract: This thesis concerns two subjects whose primary applications are in the field of cryptography: reversible programs and multi-party protocols. The first part of the thesis investigates a model of computation called a "reversible program", and its relationship to the level of cryptographic security attainable by a "simple product cipher" (which is a type of method for encrypting fixed-length blocks of data). The notion of a simple product cipher is motivated by the design of some ciphers, including the widely used Data Encryption Standard. Informally, reversible programs and simple product ciphers both have the property that they can be expressed as a composition of "very simple" permutations on the set of n-bit binary strings. We show that, under a cryptographic assumption (namely, that there exists a pseudorandom function generator that is feasibly computed by a particular kind of computation, called an "iterated integer matrix product"), there exists a cryptographically secure simple product cipher. This can be regarded as progress towards showing that a secure simple product cipher exists. A by-product of our investigation of reversible programs is a result of independent interest in the field of algebraic complexity theory: over an arbitrary ring, any polynomial-size algebraic formula is computed by an algebraic straight-line program that uses only three registers. The second part of the thesis investigates the cryptographic security attainable in two-party protocols that carry out "collective coin flipping" transactions (or "games"), and "secret bit exchanging" transactions. In both cases, we construct protocols that, under some widely believed number theoretic intractability assumptions, attain various levels of security for the transaction. We also prove some non-trivial lower bounds on the level of security attainable by any protocol for either of the transactions.

Inside a KGB cipher

Abstract: This article is an exposition of a pencil and paper cipher used by Soviet secret agents working inside the U. S. that successfully defied the government's computer-aided attempt at cryptanalysis for several years.

System for keeping secrecy of data

Abstract: PURPOSE:To always perform required enciphering and decoding against any data input by performing the enciphering and decoding so that no data exceeding a prescribed integer value can be produced by using a modulo adder and modulo subtractor. CONSTITUTION:A modulo adder 302 inputs data M1, M2,... smaller than a specific integer value N and at the same time, data B, C1,... smaller than the integer value N from a delay buffer 303 and outputs the remainder X1 produced when the sum of M1 and B is divided by N, remainder X2 produced when the sum of M2 and C1 is divided by N,.... The remainders X1, X2,... are always smaller than the integer value N and a block cipher machine 301 inputs the output data X1, X2,... of the modulo adder 302 and an enciphering key 304, and outputs enciphered sentence data C1, C2,.... Therefore, enciphering and decoding can be performed in a CBC (Cipher Block Chaining) mode by using a block cipher machine and block decoding machine which respectively perform enciphering and decoding on numerals smaller than a specific integer value N.