Part-I - Controller General of Patents Designs and Trademarks

(12) PATENT APPLICATION PUBLICATION (21) Application No.1630/CHE/2012 A
(19) INDIA
(22) Date of filing of Application :25/04/2012 (43) Publication Date : 21/06/2013
(54) Title of the invention : MODULAR EXPONENTIATION METHOD AND DEVICE RESISTANT AGAINST SIDE-
CHANNEL ATTACKS
(51) International classification :G06F 7/00
(31) Priority Document No :11305568.5
(32) Priority Date :11/05/2011
(33) Name of priority country :EPO
(86) International Application No
:NA
Filing Date
:NA
(87) International Publication No : NA
(61) Patent of Addition to Application Number :NA
Filing Date
:NA
(62) Divisional to Application Number
:NA
Filing Date
:NA
(71)Name of Applicant :
1)THOMSON LICENSING
Address of Applicant :1-5 RUE JEANNE D'ARC, 92130
ISSY LES MOULINEAUX France
(72)Name of Inventor :
1)MARC JOYE
(57) Abstract :
A modular exponentiation comprising iterative modular multiplications steps and taking as input a first modulus N, a secret
exponent d and a base x. During at least one modular multiplication step aiming at computing a result c from two values a, b and
the first modulus N so that c = ab mod N, a processor (120) takes as input the two values a, b and the first modulus N from which
are obtained two operands a, b and a second modulus AT using operations with at most linear complexity - at least one of the two
operands a, b is different from the two values a, b, and the two operands a, b are different when a is equal to b- so that the modular
multiplication c = ab mod N from a side-channel viewpoint behaves like a modular squaring except for when a equals b. An
intermediate result c = a, b mod AT is computed, and the result c is derived from the intermediate result c using an operation with
at most linear complexity; and the result c is used in the modular exponentiation.
No. of Pages : 14 No. of Claims : 9
The Patent Office Journal 21/06/2013 13868