Implementation process for the use of cryptographic data of a user stored in a data base
A security module (“SM”) implements user cryptographic data by means of a user terminal. The cryptographic data is encrypted by a first encryption key established from a secret key from the terminal and the user's authentication element and by a second encryption key specific to the SM. An authentication is performed between the SM and the terminal, based on an asymmetric cryptographic protocol, and, in the event of a positive authentication of the SM and the terminal, an authentication of the SM and the user is performed. In the event of positive authentication between the SM and the terminal and between the SM and the user, the SM obtains the user's cryptographic data, and the terminal calculates the first encryption key and sends the first encryption key to the SM. The user's cryptographic data is decrypted by the SM using the second encryption key and then the first encryption key.
1. A method for the implementation, via a security module (SM), of a user U's cryptographic data (Usk) stored in a database (BD), by means of a terminal (T) that the user uses and which communicates with the security module (SM) via a communication network (R), the method comprising the following steps and sequences:
an authentication sequence comprising the following successive steps:
mutual authentication between the security module (SM) and the terminal (T), based on an asymmetric cryptographic protocol, establishing a secure channel between the security module (SM) and the terminal (T);
in the event of a positive mutual authentication of the security module and the terminal;
mutual authentication of the security module and the user based on an asymmetric cryptographic protocol;
in the event of a positive mutual authentication between, on the one hand, the security module and the terminal and, on the other hand, the security module and the user:
the security module (SM) obtains the user's cryptographic data (Usk) from the database (BD), the cryptographic data being stored in the database (BD) in encrypted form by means of at least a first encryption key (KDF(Tsk,PIN)) established from at least one secret key from the terminal (Tsk) and the user's authentication element (PIN) and by means of a second encryption key (SMk) specific to the security module (SM), encryption by means of the second encryption key taking place after encryption by means of the first encryption key;
the terminal calculates the first encryption key (KDF(Tsk,PIN));
the terminal sends the first encryption key to the security module via the secure channel; and
implementation of the user's cryptographic data (Usk) by the security module (SM) after decryption, by the security module (SM) of the user's cryptographic data (Usk) at least first of all by means of the second encryption key (SMk) and then the first encryption key (KDF(Tsk,PIN)).
2. Method according to claim 1 , wherein the step of mutual authentication is based on:
at least one terminal authentication element (ZK(Tsk)); and
at least one user authentication element (ZK(PIN));
obtained by the security module (SM) from the database (BD), the authentication elements being stored in the database (BD) in encrypted form by means of an encryption key (SMk) specific to the security module (SM).
3. Method according to claim 2 , wherein the method uses a terminal authentication element ZK(Tsk) established at least in part from a terminal secret key (Tsk) stored in the terminal (T).
4. Method according to claim 3 , wherein the terminal authentication element comprises a proof ZK(Tsk) of possession of the terminal secret key (Tsk) via the terminal (T) intended to be used in the context of a zero disclosure authentication protocol.
5. Method according to claim 2 , wherein the user (U) authentication element (ZK(PIN) is established at least in part from a password (PIN) entered by the user (U).
6. Method according to claim 5 , wherein the user (U) authentication element comprises a proof ZK(PIN) of knowledge of the password PIN intended to be used in the context of a zero disclosure authentication protocol.
7. Method according to claim 1 , wherein the security module (SM) implements the user's cryptographic data (Usk) to perform cryptographic processing on data to be processed that is received via the communication network (R) and secured by the secure channel established during mutual authentication between the security module and the terminal.
8. Method according to claim 7 , wherein the data to be processed comprises the data used in the context of a digital signature process for an electronic document.
9. Method according to claim 1 , wherein the terminal implements a client module which manages at least communications with the security module, input of the user authentication element, the authentication sequence and calculation of the first encryption key.
10. Method according to claim 9 , wherein the client module is suitable for:
retaining the value of the client authentication element from the time of its input by the user and up to calculation of the first encryption key;
clearing the value of the authentication element after calculation of the first encryption key; and
clearing the value of the first encryption key after sending it to the security module.
11. Method according to claim 9 , wherein the client module is adapted to prevent access to the value of the client authentication element and to the value of the first encryption key via another resource or another program, from the terminal or external to the terminal, other than the security module.
12. Method according to claim 7 , wherein the client module transmits the data to be processed to the security module.
13. Method according to claim 9 , wherein the client module transmits the data to be processed to the security module.