Patent ID: 7747021

Claim:
A secure device, comprising: a vocoder configured to generate voice packets from a voice signal; a memory configured to store a previously established security association from a first session between the secure device and another secure device, wherein the stored security association comprises an encryption key and a first state vector, wherein the stored security association is adapted to be used during a second session between the secure device and the other secure device; a vector generator configured to generate an updated state vector comprising a synchronization message for maintaining secure call synchronization, wherein the vector generator comprises: a synchronization message generator configured to generate the synchronization message; an encryption engine configured to use the stored security association and the updated state vector to encrypt the voice packets; a modem configured to format the encrypted voice packets to fit within a half-duplex PTT voice channel, wherein the modem comprises: a synchronization message insertion unit configured to replace at least part of at least one of the encrypted voice packets of an encrypted voice frame being sent from the encryption engine with the synchronization message; and a first transceiver configured to transmit the formatted voice packets.