A secure real time voice communication system 70 is provided that allows
for the secure transmission of voice communications between a sending device 72
and a receiving device 78 through the public switch telephone network
76. The device 72 uses an encryption decryption engine 30 which
is capable of executing a number of encryption algorithms which are selected using
an encryption selection table 80. An encryption key can be calculated from
a periodic key value and a public variable key value. Further, the encryption algorithm
used can be periodically changed during a voice communication session so that multiple
encryption techniques can be used within the same communication session.
