Orange

France Telecom

Yannick Seurin

Henri Gilbert

Olivier Billet

Jacques Patarin

A method for converting, by means of a conversion entity, a first digit into a second digit, the first cipher corresponding to the result of a symmetric probabilistic encryption of an plain message element using a first secret matrix parameterized by a random vector, the second digit corresponding to the result of a symmetric probabilistic encryption of the plain message element using a second secret matrix that is parameterized by the random vector, characterized in that the method includes a step of: calculating the second digit by encrypting the first digit using a secret conversion matrix which is a function of the first and second secret matrices, and which is parameterized by the random vector.

Method for conversion of a first encryption into a second encryption

The invention relates to a method of probabilistic symmetric encryption of a plaintext message element with the aid of a secret key that can be represented in the form of a matrix. It comprises an operation of encrypting the plaintext message element, with the aid of the matrix parametrized by a random vector, so as to obtain an encrypted message element coupled to the random vector. Furthermore, there is envisaged a step of encoding the plaintext message element as a code word with the aid of an error correcting code having a given correction capacity and a step of adding a noise vector. The error correcting code and the noise vector are adapted so that the Hamming weight of the noise vector is less than or equal to the correction capacity of the correcting code.

Method and entity for probabilistic symmetrical encryption

The invention proposes a method and a device for decrypting an encrypted message represented by a sequence C or applying an electronic signature to a sequence C, said sequence C consisting of data belonging to a finite field K=GF(q), where q&#x3e;1, in which there are processed successive blocks each comprising (n&#xb7;d) successive data items from the sequence C, where n and d are predetermined integers greater than 1, the processing of such a block including the following steps: applying a predetermined affine invertible transformation tto said block; interpreting the resulting block as being formed of n successive elements (y, y, . . . , y) of an extension E=GF(q) of the field K; calculating an n-tuplet (x, x, . . . , x) of elements of the field E by solving a system f of n predetermined polynomials of the form in which the coefficients a, b, and cbelong to E and the exponents &#x3b1;, &#x3b2;, and &#x3b3;are positive or zero integers; interpreting said n-tuplet (x, x, . . . , x)as being a new block formed of (n&#xb7;d) successive elements from the field K; and applying a predetermined affine invertible transformation sto said new block.

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Saulx les Chartreux, France

Yannick Seurin