AUTHENTICATING ELECTRONIC KEY DEVICES

An example method may include receiving, from a key device, a first counter value and a first encoded counter value, identifying, among one or more mapping table entries in an access control unit mapping table, an access control unit mapping table entry specifying a second counter value that corresponds to the received first counter value, determining whether a second encoded counter value specified by the identified access control unit mapping table entry corresponds to the received first encoded counter value, and responsive to determining that the second encoded counter value corresponds to the received first encoded counter value, sending, to a control unit, an indication that permission is granted. The first encoded counter value may include a cryptographic encoding of the first counter value generated in view of a secret key.