International Association for Cryptologic Research

International Association
for Cryptologic Research


Howard M. Heys


Results from a Search for the Best Linear Approximation of a Block Cipher
Kashif Ali Howard M. Heys
In this paper, we investigate the application of an algorithm to find the best linear approximation of a basic Substitution-Permutation Network block cipher. The results imply that, while it is well known that the S-box used for the Advanced Encryption Standard has good nonlinear properties, it is straightforward to randomly select other S-boxes which are able to provide a similar level of security, as indicated by the exact bias of the best linear approximation found by the algorithm, rather than a simple upper bound on the maximum bias.
A Hybrid Approach to Concurrent Error Detection for a Compact ASIC Implementation of the Advanced Encryption Standard
Namin Yu Howard M. Heys
In this paper, we investigate the application of concurrent error detection circuitry to a compact application-specific integrated circuit (ASIC) implementation of the Advanced Encryption Standard (AES). The specific objective of the design is to develop a method suitable for compact ASIC implementations targeted to embedded systems such that the system is resistant to fault attacks. To provide the error detection, recognizing that previously proposed schemes are not well suited to compact implementations, it is proposed to adopt a hybrid approach consisting of parity codes in combination with partial circuit redundancy. For compact ASIC implementations, taking such an approach gives a better ability to detect faults than simple parity codes, with less area cost than proposed schemes which use full hardware redundancy. The results of the implementation analysis in this paper show that it is possible to implement an error detection scheme that is robust to multiple faults in a compact AES design such that about 39% of the overall system is devoted to the error detection functionality.
An Improved Power Analysis Attack Against Camellia's Key Schedule
Lu Xiao Howard M. Heys
This paper presents an improved simple power analysis attack against the key schedule of Camellia. While the original attack required an exact determination of the Hamming weight of intermediate data values based on power measurements, in this paper, two variants of the simple power analysis attack are presented and shown to be tolerant of errors that might occur in the Hamming weight determinations. In practical applications of the attack such errors are likely to occur due to noise and distortion in the power measurements and their mapping to the Hamming weights of the data. Further, we propose a practical method to evaluate the susceptibility of other block ciphers to simple power analysis attacks. To resist these attacks, the required design rationale of key schedules and several practical countermeasures are suggested.


Kashif Ali (1)
Stafford E. Tavares (1)
Lu Xiao (1)
Namin Yu (1)