Method for creating a secure counter on an on-board computer system comprising a chip card
According to the inventive method, the chip card, a counting function (FC), a counter (Cpt) and a private key (Cf) stored in the write-only part of the memory region are stored in a persistent memory, the counter and the private key (Cf) being accessible only by the counting function (FC). When the chip card receives a counter request emitted by an requesting entity (ER), the counting function (FC) performs a modification of the counter (Cpt) and a calculation of a signature, and sends a response to the applicant entity (ER). When the on-board system receives the response to the counter request, the signature contained in the response is checked.
1. A method to provide a secure counter on an embedded system having a chip card, the embedded system comprising a non re-writable public persistent memory; the method comprising the following operating phases:
(i) storing, in a private persistent memory of the chip card: a counting function, a counter, and a private key stored in a re-writable read-protected part of the private persistent memory, the counter and the private key being accessible solely by the counting function;
(ii) executing, upon receipt by the chip card of a counter request emitted by a requesting entity, the following operations:
(a) modifying, by the counting function, the counter ensuring uniqueness of a counter value given in reply to a given request,
(b) calculating, by the counting function, a signature using the value of the counter modified at operation (a) and the private key;
(c) sending, by the counting function, a reply to the requesting entity, the reply including the value of the counter modified at operation (a) and the signature calculated at operation (b);
(iii) verifying, upon receipt by the requesting entity of the reply to the requesting entity, the signature contained in the reply to the requesting entity with a public key or an associated public key certificate of the private key.
2. The method according to claim 1 , further comprising authenticating the requesting entity, and wherein the calculating a signature during the execution phase (ii) the counter request is only executed when authenticating the requesting entity is successful.
3. The method according to claim 1 , wherein the counter is stored encoded.
4. The method according to claim 1 , wherein modifying the counter by the counting function consists of an increment of the counter.
5. The method according to claim 1 , wherein the public key or the associated public key certificate is stored into the public persistent memory on the embedded system.
6. The method according to claim 1 , wherein the public key or the associated public key certificate is stored in the persistent memory of the chip card and returned to the embedded system at the request of the embedded system.
7. The method according to claim 1 , wherein the public key or the associated public key certificate is provided by a public key infrastructure and returned to the embedded system at the request of the embedded system.
8. The method according to claim 6 wherein the public persistent memory on the embedded system is a One Time programmable memory.
9. The method according to claim 6 , wherein the public key is an imprint of the public key.