Method to prevent power dissipation attacks on a cryptographic algorithm by implementing a random transformation step

Abstract

The invention relates to a data protection method using a cryptographic algorithm comprising at least one execution cycle of repetitive operations for processing data elements (K 2 , R 1 ) so as to generate encrypted information (C), this method comprising at least one step ( 120, 220 ) for randomly modifying the execution of at least one operation from one cycle to another, or at least one of the data elements, so that the encrypted information is unchanged by this random modification.

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       9 . Data protection method for operating a microprocessor of a chip card to protect data elements contained in a memory of the chip card from discovery by analysis of the electric power consumption of the microprocessor, said method using a symmetric cryptographic algorithm of the DES-type with a permutation step for executing operations for processing data elements so as to generate encrypted information, said method comprising: 
 operating the microprocessor to randomly determine a processing order of the bits of an input data for the execution of the permutation step, thereby protecting said data elements from discovery by analysis of the microprocessor's electric power consumption.    
   
   
       10 . The data protection method of  claim 9  wherein the cryptographic algorithm for executing operations for processing data elements includes a group of operations executed repeatedly.  
   
   
       11 . The data protection method of  claim 9  wherein said data elements are keys.