Stafford E. Tavares

Bio: Stafford E. Tavares is an academic researcher from Queen's University. The author has contributed to research in topics: Block cipher & Differential cryptanalysis. The author has an hindex of 21, co-authored 67 publications receiving 2367 citations.

On the Design of S-Boxes

Abstract: The ideas of completeness and the avalanche effect were first introduced by Kam and Davida [1] and Feistel [2], respectively. If a cryptographic transformation is complete, then each ciphertext bit must depend on all of the plaintext bits. Thus, if it were possible to find the simplest Boolean expression for each ciphertext bit in terms of the plaintext bits, each of those expressions would have to contain all of the plaintext bits if the function was complete. Alternatively, if there is at least one pair of n-bit plaintext vectors X and Xi that differ only in bit i, and f(X) and f(Xi) differ at least in bit j for all $$ \{ (i,j)|1 \leqslant i,j \leqslant n\}$$ then the function f must be complete.

The structured design of cryptographically good s-boxes

Abstract: We describe a design procedure for the s-boxes of private key cryptosystems constructed as substitution-permutation networks (DES-like cryptosystems). Our procedure is proven to construct s-boxes which are bijective, are highly nonlinear, possess the strict avalanche criterion, and have output bits which act (vitually) independently when any single input bit is complemented. Furthermore, our procedure is very efficient: we have generated approximately 60 such 4 × 4 s-boxes in a few seconds of CPU time on a SUN workstation.

Flexible access control with master keys

Abstract: We show how to create a master key scheme for controlling access to a set of services. Each master key is a concise representation for a list of service keys, such that only service keys in this list can be computed easily from the master key. Our scheme is more flexible than others, permitting hierarchical organization and expansion of the set of services.

Cryptanalysis of RC4-like Ciphers

Abstract: RC4, a stream cipher designed by Rivest for RSA Data Security Inc., has found several commercial applications, but little public analysis has been done to date. In this paper, alleged RC4 (hereafter called RC4) is described and existing analysis outlined. The properties of RC4, and in particular its cycle structure, are discussed. Several variants of a basic "tracking" attack are described, and we provide experimental results on their success for scaled-down versions of RC4. This analysis shows that, although the full-size RC4 remains secure against known attacks, keystreams are distinguishable from randomly generated bit streams, and the RC4 key can be recovered if a significant fraction of the full cycle of keystream bits is generated (while recognizing that for a full-size system, the cycle length is too large for this to be practical). The tracking attacks discussed provide a significant improvement over the exhaustive search of the full RC4 keyspace. For example, the state of a 5 bit RC4-like cipher can be obtained from a portion of the keystream using 242 steps, while the nominal keyspace of the system is 2160. More work is necessary to improve these attacks in the case where a reduced keyspace is used.

A Fast VLSI Multiplier for GF(2 m )

Abstract: Multiplication in the finite field GF(2^{m} ) has particular computational advantages in data encryption systems. This paper presents a new algorithm for performing fast multiplication in GF(2^{m} ), which is O(m) in computation time and implementation area. The bit-slice architecture of a serial-in-serial-out modulo multiplier is described and the circuit details given. The design is highly regular, modular, and well-suited for VLSI implementation. The resulting multiplier will have application in algorithms based on arithmetic in large finite fields of characteristic 2, and which require high throughput.

Handbook of Applied Cryptography

Abstract: 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.

PRESENT: An Ultra-Lightweight Block Cipher

Abstract: With the establishment of the AES the need for new block ciphers has been greatly diminished; for almost all block cipher applications the AES is an excellent and preferred choice. However, despite recent implementation advances, the AES is not suitable for extremely constrained environments such as RFID tags and sensor networks. In this paper we describe an ultra-lightweight block cipher, present . Both security and hardware efficiency have been equally important during the design of the cipher and at 1570 GE, the hardware requirements for present are competitive with today's leading compact stream ciphers.

[서평]「Applied Cryptography」

Abstract: The objective of this paper is to give a comprehensive introduction to applied cryptography with an engineer or computer scientist in mind. The emphasis is on the knowledge needed to create practical systems which supports integrity, confidentiality, or authenticity. Topics covered includes an introduction to the concepts in cryptography, attacks against cryptographic systems, key use and handling, random bit generation, encryption modes, and message authentication codes. Recommendations on algorithms and further reading is given in the end of the paper. This paper should make the reader able to build, understand and evaluate system descriptions and designs based on the cryptographic components described in the paper.

PRESENT: An Ultra-Lightweight Block Cipher

Abstract: With the establishment of the AES the need for new block ciphers has been greatly diminished; for almost all block cipher applications the AES is an excellent and preferred choice. However, despite recent implementation advances, the AES is not suitable for extremely constrained environments such as RFID tags and sensor networks. In this paper we describe an ultra-lightweight block cipher, present . Both security and hardware efficiency have been equally important during the design of the cipher and at 1570 GE, the hardware requirements for present are competitive with today's leading compact stream ciphers.