An encryption code and at least one key are provided to a secure transmission device, via an external keying device, and stored in a volatile memory. A user code, entered via a keypad by a user, is received by the secure transmission device. An encrypted representation of the at least one key, based...http://www.google.ca/patents/US5412721?utm_source=gb-gplus-sharePatent US5412721 - Method for loading and utilizing a key in a secure transmission device
