Patent ID: 7123717

Claim:
A method for decrypting an encrypted message in electronic microprocessors in conjunction with a terminal, making it possible to not disclose information relating to secret data through current consumption of the microprocessor executing the instructions of a program that performs a random calculation modulus at each new execution of an RSA decryption algorithm using the Chinese Remainder Theorem, said method using as inputs a message c, a decryption exponent d and a security parameter s, to generate a decrypted message m, comprising the following steps: 1) Select three random numbers r, t and u between 0 and 2^s; 2) Calculate p′=p*r and q′=q*t, p and q being two distinct prime numbers of the same size; 3) Replace c by c+u*n, where n is the calculation modulus; 4) Calculate cp=c modulo p′ and cq=c modulo q′; 5) Calculate dp=d′ modulo p−1 and dq=d′ modulo q−1; 6) Calculate mp′=cp^dp modulo p′ and mq′=cq^dq modulo q′; 7) Calculate m=((mq−mp)*(p^(−1) mod q) mod q′)*p+mp; 8) Replace m by m mod n to thereby generate the decrypted message.