An electronic door lock system comprising a door control unit, a key reader and an encrypted binding between the key reader and the door control unit. When tampering is detected the encrypted binding is terminated thereby preventing the door from being opened. There is also disclosed a method for retrofitting a door comprising a key reader with a door control unit. The door control unit, key reader and the latch release mechanism may also be powered by a key comprising a power supply, the key also supplying a coded sequence to the door control unit.