Thales

Sandrine Agagliate

Eric Garrido

Philippe Painchault

Renaud Dubois

The invention relates to a method for broadcasting data in a system using a BES (A) stateless scheme using a binary tree T with a KEKs No 2 key structure, i.e. such that a key kis associated with each difference of subsets S, and a root key kassociated with the set of the tree T and a BES (A) 'stateful' scheme using the same binary tree T with a KEKs No 1 key structure, i.e. such that a key kis associated with each subtree Swherein the scheme (A) is used for the current broadcast session and the keys known by the denied users are updated with a 'stateful' scheme (A) from time to time.

Hybrid method for distributing keys for the diffusion of encrypted data

A method for managing keys making it possible for a user to access one or more given services S in a communication system, in which the user is not able to be continuously connected to this service. A key K(t) is generated, which provides access to the service of day [t] for all the t&#x3c;tby using a one-way function in the following manner (a one-way function being defined as being a function for which it is not currently possible by computing means to obtain the inverse function). A root key K(t) is used and the key K(t) is generated for the day [t] prior to the day t, by using a function f such that K(t&#x2212;1)=f(K(t)). The new value of key K(t) is used in order to generate the key for the previous day K(t) and this step is reiterated over the limited time period of day [t] to day [t+d] in order to obtain the chain K(t+d&#x2212;1), K(t+d&#x2212;2), etc. Each day t the key K(t+d) is sent to the users or user group having a trust level d (giving potential access to the service for d consecutive days).

Method for managing and controlling the access keys to services in a communication system

Method and system are disclosed for managing erratic interruptions in a transmission system where the messages to be transmitted are composed of data packets and are expressed by means of a polynomial of degree t&#x2212;1. The senders and the receivers share information making it possible to reference the data packets. In the course of the transmission of a message represented by a polynomial P, at least t points Ai are generated and P(Ai) of the polynomial P is evaluated, with t' greater than or equal to t. The evaluations P(Ai) are transmitted of the t&#x2032; points to the receiver or receivers concerned, with information allowing the receivers to detect the transmission errors. Each receiver verifies that it has received t valid evaluations, that is to say free of transmission errors, uses the information referencing the packets and the t valid evaluations P(Ai) of the polynomial to determine the points Ai, and on the basis of the P(Ai) and of the Ai and determines the polynomial P used and on the basis of said polynomial deduces the message therefrom.

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Paris, France

Sandrine Agagliate