Method and system of using an insecure crypto-accelerator

A method for performing calculations using a secret bitstring and a cipher key using an insecure processor, said method comprising:

• dividing said cipher key into first and second parts;
• computing, in a secure processor, a third product as a function of said bitstring and said first part of said cipher key;
• outputting said third product to said insecure processor;
• modifying said second part of said cipher key with said secure processor to obtain a modified second part of said cipher key;
• generating an indicator corresponding to said modified second part of said cipher key;
• computing a first product with said insecure processor as a function of said third product and said modified second part of said cipher key;
• computing a second product with said secure processor as a function of said bitstring and said indicator;
• and
• computing a final product with said secure processor as a function of said first product and said second product.

A computing device for exponentiating a bitstring with a secret exponent, said computing device comprising a secure processor and an insecure processor, wherein said secure processor is programmed to:

• divide said secret exponent into a plurality of partial values comprising a least a first partial value and a second partial value such that the sum of said plurality of partial values is equal to said exponent;
• output said first partial value to an insecure processor;
• receive a first product from said insecure processor computed as a function of said bitstring and said first partial value;
• compute a second product as a function of said second partial value and said bitstring;
• and
• compute a final product as a function of said first product and a second product.