Towards a general model for secure speech communications

Abstract

It is clear that the activities of an increasingly information-centered societal infrastructure are driving the rapid expansion of digital communications technology. The demand for services integrating voice, data, and video traffic is increasing with the technical sophistication of the consumer, and has already spawned a host of alternative including ISDN, cellular, cable modem, personal communication systems, and Internet technologies. These technologies all represent steps in the evolution towards a global digital communications strategy. We will examine issues surrounding the implementation of speech services in a secure digital communications environment.

The reasons for the emergence of digital speech communications systems lie in their advantages over the older analog systems. These include improved signal quality, error recovery capabilities, and the ability to multiplex a signal with other conversations or with an entirely different form of digital service. Digital service also allows a significant improvement in the ability to protect a conversation from unwelcome scrutiny. This is fast becoming an important issue in the design of information systems. In the information age we have come to recognize that there is intrinsic value in most forms of communication, and that ensuring privacy can be tantamount to protecting material assets.

The addition of a cryptographic component into a speech communication system adds complications that are not encountered in a conventional system. The characteristics of an encryption coder increase the challenge of secure system design. The system designer must balance the requirements for high security and subjective speech quality with the conflicting desires for a low channel bit rate and limited system complexity. The optimal choice of source, encryption, and channel coder components to meet these objectives requires a thorough understanding of a large set of interrelated parameters.

In this research we will develop models of objective speech quality, bit rate, security, and complexity that are relevant to the design of an integrated secure speech communication system. We will present experimental and theoretical evidence leading to an understanding of the interrelationships among the parameters of the secure system. The parameter models will then be integrated to define a multidimensional constrained optimization problem as a general model for the secure speech communication system.