France Telecom

David Lefranc

Marc Girault

A technique for secure delegation of calculation of a value f(X,Y) of a bilinear application in a computational server. The technique comprises selection of two secret parameters a and b; calculation of the numbers Xand Y; supply of the two numbers Xand Yto the computational server; calculation of f(X, Y) by said server; receipt of the value of f(X,Y) from the server; extraction of the abroot of f(X,Y).

Method for secure delegation of calculation of a bilinear application

A method and device for performing a cryptographic operation by a device controlled by a security application executed outside thereof in which a cryptographic value (y) is produced a calculation comprising at least one multiplication between first and second factors containing a security key (s) associated with the device and a challenge number (c) provided by the security application. The first multiplication factor comprises a determined number of bits (L) in a binary representation and the second factor is constrained in such a way that it comprises, in a binary representation, several bits at 1 with a sequence of at least L&#x2212;1 bits at 0 between each pair of consecutive bits to 1 while the multiplication is carried out by assembling the binary versions of the first factor shifted according to positions of the bits at 1 of the second factor, respectively.

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Caen, France

David Lefranc