There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

From the Publisher:
A valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography, this book provides easy and rapid access of information and includes more than 200 algorithms and protocols; more than 200 tables and figures; more than 1,000 numbered definitions, facts, examples, notes, and remarks; and over 1,250 significant references, including brief comments on each paper.

Handbook of Applied Cryptography

A new signature scheme is proposed, together with an implementation of the Diffie-Hellman key distribution scheme that achieves a public key cryptosystem. The security of both systems relies on the difficulty of computing discrete logarithms over finite fields.

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A public key cryptosystem and a signature scheme based on discrete logarithms

For many applications, a randomized algorithm is either the simplest or the fastest algorithm available, and sometimes both. This book introduces the basic concepts in the design and analysis of randomized algorithms. The first part of the text presents basic tools such as probability theory and probabilistic analysis that are frequently used in algorithmic applications. Algorithmic examples are also given to illustrate the use of each tool in a concrete setting. In the second part of the book, each chapter focuses on an important area to which randomized algorithms can be applied, providing a comprehensive and representative selection of the algorithms that might be used in each of these areas. Although written primarily as a text for advanced undergraduates and graduate students, this book should also prove invaluable as a reference for professionals and researchers.

Randomized Algorithms

We discuss the use of elliptic curves in cryptography. In particular, we propose an analogue of the Diffie-Hellmann key exchange protocol which appears to be immune from attacks of the style of Western, Miller, and Adleman. With the current bounds for infeasible attack, it appears to be about 20% faster than the Diffie-Hellmann scheme over GF(p). As computational power grows, this disparity should get rapidly bigger.

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Use of Elliptic Curves in Cryptography

Matrix multiplication via arithmetic progressions

We present a new method for accelerating matrix multiplication asymptotically. This work builds on recent ideas of Volker Strassen, by using a basic trilinear form which is not a matrix product. We make novel use of the Salem-Spencer Theorem, which gives a fairly dense set of integers with no three-term arithmetic progression. Our resulting matrix exponent is 2.376.

We show how to find sufficiently small integer solutions to a polynomial in a single variable modulo N, and to a polynomial in two variables over the integers. The methods sometimes extend to more variables. As applications: RSA encryption with exponent 3 is vulnerable if the opponent knows two-thirds of the message, or if two messages agree over eight-ninths of their length; and we can find the factors of N=PQ if we are given the high order $\frac{1}{4} \log_2 N$ bits of P.

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Small Solutions to Polynomial Equations, and Low Exponent RSA Vulnerabilities

The Data Encryption Standard (DES) was developed by an IBM team around 1974 and adopted as a national standard in 1977. Since that time, many cryptanalysts have attempted to find shortcuts for breaking the system. In this paper, we examine one such attempt, the method of differential cryptanalysis, published by Biham and Shamir. We show some of the safeguards against differential cryptanalysis that were built into the system from the beginning, with the result that more than 10 15 bytes of chosen plaintext are required for this attack to succeed.

The Data Encryption Standard (DES) and its strength against attacks

We show how to solve a polynomial equation (mod N) of degree k in a single variable x, as long as there is a solution smaller than N1/k. We give two applications to RSA encryption with exponent 3. First, knowledge of all the ciphertext and 2/3 of the plaintext bits for a single message reveals that message. Second, if messages are padded with truly random padding and then encrypted with an exponent 3, then two encryptions of the same message (with different padding) will reveal the message, as long as the padding is less than 1/9 of the length of N. With several encryptions, another technique can (heuristically) tolerate padding up to about 1/6 of the length of N.

/pdf/finding-a-small-root-of-a-univariate-modular-equation-5cb1vq8jwm.pdf

Don Coppersmith

Papers

Matrix multiplication via arithmetic progressions

Matrix multiplication via arithmetic progressions

Small Solutions to Polynomial Equations, and Low Exponent RSA Vulnerabilities

The Data Encryption Standard (DES) and its strength against attacks

Finding a small root of a univariate modular equation