A method for encrypting bill validation data generated by a bill validator is disclosed. Such data includes an inserted bill's denomination and country of origin as determined by sensors in the bill validator. Once such information is obtained, it is encrypted by combination with an encryption key selected from a table of such keys. The encrypted data is then communicated to a machine associated with the bill validator such as a gaming or vending machine. Upon receipt, the machine decrypts the data to obtain the original bill validation data. If the machine finds the denomination and issuing country of the inserted bill to be acceptable, the machine instructs the bill validator to accept the bill and store it in a bill repository.