METHOD SECURED AGAINST SIDE-CHANNEL ATTACKS WITH A NEW MASKING SCHEME PROTECTING LINEAR OPERATIONS OF A CRYPTOGRAPHIC ALGORITHM

摘要

The present invention relates to a method secured against side channel attacks performing an operation (f) of a cryptographic algorithm on an input message in a whitebox implementation using a cryptographic key, said operation being linear with a Boolean exclusive OR (XOR) operation or an arithmetic operation (+), wherein : said method is performed by a client device comprising at least one hardware processor and a random generator and comprises : - generating (S1) a first mask and a second mask (m_k, m_x) by said random generator, - obtaining (S2) an encoded chunk of the cryptographic key (E'_k(k)) and an encoded chunk of the input message (E'_x(x)), - determining (S31) an encoded value (E_k(k⊕m_k)) of the chunk of the cryptographic key masked with the first mask (m_k), by using at least one look up table mapping the obtained encoded chunk of the cryptographic key (E'_k(k)) and the first mask (m_k) to said encoded value of the masked chunk of the cryptographic key (E_k(k⊕m_k)), - determining (S32) an encoded value (E_x(x⊕ m_x)) of the chunk of the input message (x) masked with the second mask (m_x), by using at least one look up table mapping the obtained encoded chunk of the input message (E'_x(x)) and the second mask (m_x) to said encoded value of the masked chunk of the input message (E_x(x⊕ m_x)), - determining (S4) an encoded value (E_y(y⊕m_x⊕m_k)) of the result (y) of performing said operation (f) on the chunk of the cryptographic key (k) and on the chunk of the input message (x), masked with the first and second masks, by using at least one look up table mapping the determined encoded value of the chunk of the cryptographic key masked with the first mask (E_k(k⊕m_k)) and the determined encoded value of the chunk of the input message masked with the second mask (E_x(x⊕ m_x)) to said encoded value of the masked result of said operation (E_y(y⊕m_x⊕m_k)).