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(11)    Patent No :    AP 1949   
(21)    Application No :    AP/P/2005/003444   
(22)    Filing Date :    02.09.2004   
(24)    Date of Grant &    05.02.2009   
(45)    Publication :

(30)  Priority Data       
(33) Country    (31) Number    (32) Date
EP    03103307.9    05.09.2003

(84)    Designated State

BW    GM    GH    KE    LS    MW  MZ   NA   SL
SD    SZ    T Z    UG    ZM    ZW
(73) Applicant(s)

NAGRAVISION S. A., Route de Geneve, 22, CH-1033 Cheseaux-sur-Lusanne,

(72) Inventors

VAUDENAY Serge, Switzerland

JUNOD Pascal, Switzerland

(74) Representative


(51)  International  Classification   H04L 9/06 (2006.01)    H04L 9/22 (2006.01)

(54)    Title

Method for generating pseudo-random sequence.

(57)    Abstract

The aim of this invention is to propose a method to generate sequences or sub-keys based on a main key, in which each sub-key gives no information to recover the main key or any other sub-keys. The aim is achieved with a method to generate sub-keys based on a main key (MKEY), comprising the following steps: - obtaining a first value (Al) by applying to the main key (MKEY) a linear diversification layer by mixing the main key (MKEY) with a constant, - applying to the first value (Al) a non-linear transformation, this transformation comprising the steps of: - obtaining a second value (A2) by applying the first value (Al) to a substitution layer, the substitution layer comprising at least one substitution box (sbox), each substitution box containing at least one table of constants for which the input serves as the pointer and the pointed constant serves as the output, - obtaining a third value (A3) by using a diffusion box of multi-permutation type based on the second value (A2), - dividing the third value (A3) in N blocks of same size, obtaining the output fourth value (A4) formed by N blocks, each block of the fourth value (A4) being the result of the combination of N-I blocks of the third

value (A3), the missing block being the block of the same index. - obtaining the fifth value (A5) by applying to the fourth value (A4) a substitution layer, - obtaining the sub-key (RKEY) by applying to the fifth value (A5) a symmetrical

(56)    Documents Cited :    US 5 745 577 A   US 2002/044651 A


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