Abstract: A method for allocating a first range of identifiers to a customer-system from a register. The method comprising the steps of: receiving a request for identifiers from a new customer-system; identifying a largest range of unallocated identifiers to define an available range within the entire range of identifiers belonging to the register; identifying a midpoint in the largest available range; and allocate the identified midpoint as a start location for the customer-system range. Identifiers can be issued as identifier pairs, one being an encrypted identifier and the other being a corresponding unencrypted identifier.