METHOD AND DEVICE FOR RANDOMIZING A SECRET KEY FOR PROTECTING AGAINST ATTACKS BY AUXILIARY CHANNELS

摘要

The invention relates to a method for randomizing components S₁ ⁽⁰⁾' …' S_D+1⁽⁰⁾, belonging to a group G, of a reference mask for a secret key k, characterized in that it comprises at least the following steps: 1 - using the components of a reference mask for the given key k, S₁⁽⁰⁾' …' S_D+1⁽⁰⁾ G a group provided with an internal operation O with k = S₁⁽⁰⁾ O …O S_D+1(0)' executing a loop on i=0 to λ-1 including the following steps 2 and 3: 2 - generating a new reference or working mask for said key k using a randomizer (7) producing the first D components of the mask of iteration i+1 where D and λ are security parameters (s₁⁽ⁱ⁺¹⁾,...,S_D(ⁱ⁺¹)←rand(G^D); 3- then determining the last component S_D+1⁽ⁱ⁺¹⁾ of the working or reference mask of iteration i+1 by combining the components S₁⁽ⁱ⁾' …' S_D+1⁽ⁱ⁾ of the mask of iteration i with the components S₁⁽ⁱ⁺¹⁾' …, S_D⁽ⁱ⁺¹⁾ of the mask of iteration i+1 generated in step 2, while observing an alternation of a component of iteration i and a component of iteration i+1; 4 - after λ iterations of steps 2 and 3 carried out in order to obtain said mask of components (S₁^(λ)' …'S_D+1^(λ), using said mask either to update the reference mask, or to execute a cryptographic process.