France Telecom

Orange

David Arditti Modiano

Marc Girault

Henri Gilbert

Sébastien Canard

Jacques Traore

Dimitri Mouton

Laurent Frisch

Oliver Billet

A traceable method for encrypting and/or decrypting data broadcast by at least one transmitter towards several decoders includes the steps: during encryption of broadcast data, the transmitter implements (in) at least one first secret function to transform an unencrypted message into an encrypted message; and during decryption of the broadcast data, all the decoders implement (in) at least one common second secret function, each decoder using therefor a mathematical description of the second function stored in a memory (), the mathematical description of the second function being different from one decoder to another or from one group of decoders to another such that the mathematical description used identifies exclusively the particular decoder or group of decoders.

Traceable method and system for encrypting and/or decrypting data, and recording media for implementing the method

The invention concerns a system enabling a member (M) of a group (G) to produce, by means of customized data (z; K), a message (m) accompanied by a signature () proving to a verifier that the message originates from a member of the group (G). The invention is characterized in that the customized data is in the form of an electronic physical medium (). Advantageously, the latter also incorporates: encrypting means (B) for producing a customized cipher (C) from the customized data prior to the signature S of the message (m), means (B) for producing a combination of a message m to be signed and the cipher (C) associated with said message, for example in the form of a concatenation of the message (m) with the cipher (C), and means (B) for signing (Sig) the message (m) with the customized data (z; K) in the form of a cipher (C) associated with said message. Advantageously, the physical medium is a smart card () or the like.

Cryptographic system for group signature

A ring-signature scheme is adapted so that at least one of the variability parameter values used is an identity trace of the anonymous signatory, determined as a function of anonymity withdrawal data stored and held secret by an anonymity withdrawal entity in connection with an identification of the anonymous signatory. This provides a subsequent controlled capacity of withdrawing the anonymity of the signatory, either by an authority, or by the signatory himself.

Electronic group signature method with revocable anonymity, equipment and programs for implementing the method

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Clamart, France

David Arditti Modiano