Improved Alpha-Information Bounds for Higher-Order Masked Cryptographic Implementations

Embedded cryptographic devices are usually protected against side-channel attacks by masking strategies. In this paper, the security of protected cryptographic implementations is evaluated for any masking order, using alpha-information measures. Universal upper bounds on the probability of success of any type of side-channel attack are derived. These also provide lower bounds on the minimum number of queries required to achieve a given success rate. An important issue, solved in this paper, is to remove the loss factor due to the masking field size.