Controlling access to an access object

1. A method for controlling access to an access object, the method being performed in an access control device and comprising the steps of:

receiving a user input to reset the access control device;

generating a unique new identifier for the access control device, and discarding, from the access control device, all previously used identifiers for the access control device to thereby invalidate all previous access delegations relating to the access control device;

communicating with an electronic key to obtain an identity of the electronic key;

obtaining a plurality of delegations, wherein each delegation is a delegation from a delegator to a receiver; and

granting access to the access object only when the plurality of delegations comprise a sequence of delegations covering a delegation path from the access control device, identified using the new identifier, to the electronic key such that, in the sequence of delegations, the delegator of the first delegation is the access control device, and the receiver of the last delegation is the electronic key.

2. The method according to claim 1 , wherein in the step of generating a unique new identifier, the new identifier comprises at least one cryptographic key pair.

3. The method according to claim 1 , further comprising the step of:

receiving an input to store the first delegation in storage of the access control device.

4. The method according to claim 1 , wherein the step of obtaining a plurality of delegations comprises obtaining at least one delegation from the electronic key.

5. The method according to claim 4 , wherein each delegation obtained from the electronic key is digitally signed by the delegator of the respective delegation.

6. The method according to claim 1 , further comprising the step of:

evaluating time constraints of all of the plurality of delegations and wherein the step of granting access is only performed when none of the time constraints are violated.

7. The method according to claim 1 , further comprising the step of:

evaluating operation constraints of all of the plurality of delegations and wherein the step of granting access is only performed when none of the operation constraints deny the granting access operation.

8. An access control device for controlling access to an access object, the access control device comprising:

a processor; and

a memory storing instructions that, when executed by the processor, causes the access control device to:

receive a user input to reset the access control device;

generate a unique new identifier for the access control device, and discard all previously used identifiers for the access control device thereby invalidating all previous access delegations relating to the access control device;

communicate with an electronic key to obtain an identity of the electronic key;

obtain a plurality of delegations, wherein each delegation is a delegation from a delegator to a receiver; and

grant access to the access object only when the plurality of delegations comprise a sequence of delegations covering a delegation path from the access control device, identified using the new identifier, to the electronic key such that, in the sequence of delegations, the delegator of the first delegation is the access control device, and the receiver of the last delegation is the electronic key.

9. The access control device according to claim 8 , further comprising the instructions that, when executed by the processor, causes the access control device to:

receive an input to store the first delegation in storage of the access control device.

10. The access control device according to claim 9 , wherein the instructions to obtain a plurality of delegations comprise instructions that, when executed by the processor, causes the access control device to obtain at least one delegation from the electronic key.

11. The access control device according to claim 10 , wherein each delegation obtained from the electronic key is digitally signed by the delegator of the respective delegation.

12. A computer program for controlling access to an access object, the computer program comprising computer program code which, when run on a access control device causes the access control device to:

receive a user input to reset the access control device;

generate a unique new identifier for the access control device, and discard all previously used identifiers for the access control device to thereby invalidate all previous access delegations relating to the access control device;

communicate with an electronic key to obtain an identity of the electronic key;

obtain a plurality of delegations, wherein each delegation is a delegation from a delegator to a receiver; and

grant access to the access object only when the plurality of delegations comprise a sequence of delegations covering a delegation path from the access control device, identified using the new identifier, to the electronic key such that, in the sequence of delegations, the delegator of the first delegation is the access control device, and the receiver of the last delegation is the electronic key.

13. A computer program product comprising a computer program according to claim 12 and a computer readable means on which the computer program is stored.