![]() ![]() making a mother key in the security means correspond to the identifier of the second controller, transmitting the identifier of the second controller and an identifier of the selected application from the second controller to a distant security means through the first controller, To this end, a method for protecting data exchanges between first and second controllers, the first controller managing communications to a telecommunications network for applications implemented in the second controller, the second controller containing a controller identifier and keys for the applications derived from a mother key, is characterised by the following steps for each application selected in the second controller: The invention aims to mitigate the inadequacies of the prior art at least for the particular context above, so as to protect a data exchange between the controllers of any card and any additional card. Obtaining only one of these mother keys associated with only one of the SIM cards would make it possible to manufacture clones of any additional card. This principle is precisely flouted if the SIM cards contain the mother key. This is because, with regard to security, if a card is “broken”, that is to say if all the keys which it contains are obtained, under no circumstances should all the security means be threatened. In addition to the practical aspect of the storage of the mother keys in all the SIM cards, there is a very great risk in entrusting the mother key to all the users. It is therefore impossible to pre-store all the mother keys of the additional cards in the SIM identity cards. The telephone operator selling the SIM cards is incapable of providing, when they are parameterised, for the introduction of all the mother keys into each SIM card, relating to the various additional cards or to the applications which they contain. ![]() In this case, the user of each terminal can acquire various additional cards emanating from various card issuers, and a priori each containing several applications. The other legal entity is an issuer of application smart cards, referred to as additional cards, each containing a “second” controller, which are introduced into additional card readers in terminals. According to an example to which reference will be made hereinafter, one of the legal entities is the operator of a radio telephony network who sells removable identity smart cards or SIM (Subscriber Identity Module) cards in mobile radio telephony terminals, which each contain a “first” controller. However, the invention relates more particularly to another context in which two controllers emanate from two distinct legal entities who a priori are not sufficiently connected for one to impose security data on the other. The daughter key of a second controller results from the application of the mother key and a serial number of the second controller, the smart card, to a key diversification algorithm. ![]() To protect the dialogue between the two controllers, one known solution consists of pre-storing a mother key in the first controller, such as for example that of a security module in a point of sale terminal, and pre-storing daughter keys in second controllers for user smart cards, such as credit cards or electronic purse cards. The present invention concerns the protection of data exchange between two controllers. ![]()
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