Computation of a multiplication operation with an electronic circuit and method

1. A computing method performed by an electronic circuit for computing a modular reduction operation of at least one operand by a modulus, the method comprising:

in a subtraction circuit, generating a first intermediate result representing a first intermediate result initialized with a value representing two to the power of k reduced by the modulus, where k designates the number of bits representing the modulus;

generating a second intermediate result with the k lowest significant bits of said operand, at least comprising iteratively for each bit of said operand;

in an addition circuit, if the state of the current bit of said operand is one, updating the second intermediate result by adding in the first intermediate result;

in a shifting circuit, doubling the value of a first intermediate result by shifting the bits of the first intermediate result towards the most significant bit, where the most significant bit is the k+1th bit;

in the subtraction circuit, while the most significant bit of the first intermediate result is one, updating the first intermediate result by subtracting the modulus;

in the subtraction circuit, and while the most significant bit of the second intermediate result is one, updating the second intermediate result by subtracting the modulus; and

in the subtraction circuit, generating an output of the modular reduction operation by updating the second intermediate result by subtracting the modulus if the second intermediate result is greater than the modulus.

2. An integrated circuit having a modular operation comprising a computation core receiving a first value and a second value representing the modulus, and providing an updated first value, said core comprising:

the shifting circuit;

the subtraction circuit; and

a control unit to perform the iterative steps of the computation according to the method of claim 1 .

3. The circuit of claim 2 , integrated in a processing unit of cryptographic algorithms.

4. A Set Top Box comprising a circuit according to claim 2 .

5. A circuit, comprising:

a subtraction circuit configured to generate a first intermediate result initialized with a value representing two to the power of k reduced by a modulus, where k designates the number of bits representing the modulus, the subtraction circuit further configured to generate a second intermediate result with the k lowest significant bits of an operand, at least comprising iteratively for each bit of the operand;

an addition circuit configured to update the second intermediate result by adding in the first intermediate result if the state of the current bit of the operand is one;

a shifting circuit configured to double the value of a first intermediate result by shifting the bits of the first intermediate result towards the most significant bit, where the most significant bit is the k+1th bit;

such that the subtraction circuit, while the most significant bit of the first intermediate result is one, is configured to update the first intermediate result by subtracting the modulus, and while the most significant bit of the second intermediate result is one, configured to update the second intermediate result by subtracting the modulus;

the subtraction circuit further configured to generate an output of the modular reduction operation by updating the second intermediate result by subtracting the modulus if the second intermediate result is greater than the modulus; and

a control circuit coupled to the subtraction, addition, and shifting, circuits and operable to the control the operation of these circuits.

6. The circuit of claim 5 wherein the control circuit controls the subtraction, addition, and shifting, circuits to utilize the output to encrypt data words.

7. An electronic system, comprising;

electronic circuitry operable to perform a desired function; and

an encryption/decryption circuit coupled to the electronic circuitry, the encryption/decryption circuit including,

a subtraction circuit configured to generate a first intermediate result initialized with a value representing two to the power of k reduced by a modulus, where k designates the number of bits representing the modulus, the subtraction circuit further configured to generate a second intermediate result with the k lowest significant bits of an operand, at least comprising iteratively for each bit of the operand;

an addition circuit configured to update the second intermediate result by adding in the first intermediate result if the state of the current bit of the operand is one;

a shifting circuit configured to double the value of a first intermediate result by shifting the bits of the first intermediate result towards the most significant bit, where the most significant bit is the k+1th bit;

such that the subtraction circuit, while the most significant bit of the first intermediate result is one, is configured to update the first intermediate result by subtracting the modulus, and while the most significant bit of the second intermediate result is one, configured to update the second intermediate result by subtracting the modulus;

the subtraction circuit further configured to generate an output of the modular reduction operation by updating the second intermediate result by subtracting the modulus if the second intermediate result is greater than the modulus; and

a control circuit coupled to the subtraction, addition, and shifting, circuits and operable to the control the operation of these circuits.

8. The electronic system of claim 7 wherein the electronic circuitry comprises one of set top box, computer, portable audio player, and video player circuitry.

9. The method of claim 1 , further comprising updating the second intermediate result again by subtracting the modulus if the current value of the second intermediate result is greater than the value of the modulus.

10. The method of 1 wherein a control circuit controls the subtraction, addition, and shifting, circuits to utilize the output to decrypt data words.