Deploying and provisioning wireless handheld devices

In order to exchange one or more messages, the method of establishing the two-way communication course between this 1st system and the 2nd system which are performed by the 1st system is indicated. The pair of the 1st key which has the 1st public key and 1st secret key is generated, and the pair of the 2nd key which has the 2nd public key and 2nd secret key is generated. The 2nd public key is generated based on the shared secrecy which is known to the 1st system and 2nd system. The 2nd public key and 1st public key are transmitted to the 2nd system. The 3rd public key and 4th public key that are generated by the 2nd system are received, and the 4th public key is generated based on the shared secrecy. A master key is calculated based on the 1st secret key, this 2nd secret key, this 3rd public key, and this 4th public key, and the master key is constituted so that it may be used in encryption of one or more messages.