Key encryption system and method, pager unit, and pager proxy for a two-way alphanumeric pager network

A method and system allows encryption services can be added to an existing wireless two-way alphanumeric pager network by providing a pager proxy which is arranged to receive an encrypted message from a sending pager and re-packages it for re-transmission to the destination pager. The sending pager encrypts the message using a session key, and encrypts the session key so that it can only be recovered by a secret key of the pager proxy. The pager proxy, upon recovery of the session key, decrypts the message, generates a new session key, re-encrypts the message, and encrypts the new session key so that it can only be recovered by a secret key of the destination pager. Encryption of the session key can either be carried out by shared secret key encryption or encryption of the session key by a public key corresponding to a private key of the pager proxy or destination pager. Authentication of the sending pager and proxy server is provided by encryption of the session keys together with identifying data, and authentication of the message is provided by a message authentication code generated by computing a message authentication code based on the session key, identifying data, and the message.