Voice Encryption - Why We Need It?

Why do I need Encryption?
Any general discussion on the need for voice encryption makes a few assumptions. These being, that the user of a communications system believes that;

1. a real or perceived threat exists in voice traffic collection from source who has the technical and financial means to collect and extract information from a communications system.
2. the information on the system is of some value to persons other than the sender and the intended receiver(s), e.g., personal; financial; intelligence; or otherwise information that is sensitive in nature.

If my voice audio circuit is already digitized; why do I need voice encryption?
The average eavesdropper with a simple analog radio or telephone wire tap may not be a real threat against a modern digitized communications channel, however, most people would agree that the 'average eavesdropper' is not representative of their threat. The standards placed on communications systems are global in nature, and the boxes that can intercept (monitor) most communications protocols 'off-the-shelf' purchases. Therefore, digitization alone only protects your voice channel from the 'casual listener' who's budget does not include the necessary, commercially available, monitoring products.

Voice Encryptor and Voice Circuit Types:

1. The Digital Voice Encryptor. The digital voice encryptor treats the voice signal as a digital data stream, and is therefore closer to a data encryptor than a voice encryptor in terms of its performance characteristics. It relies on some method of converting the voice signal into a digital data stream. Once it is digitized, it is then 'Exclusive ORed' with the key stream generator's output bit stream, thus producing the encrypted data stream signal sent out over the channel.
2. The Analog Voice Encryptor. Early methods of 'analog' encryption were nothing more than voice scrambles with little security to any aggressive attack. The advent of more powerful voice processing circuitry and software allowed more sophisticated voice processing techniques that use a key generator's secure key stream for selecting the given sound segment's permutations. There purmutations include band segmentation, sub-band frequency inversions (or non-inversions), and sub-band segment interleaving. The more combinations used, the harder to reconstruct the signal without knowledge of the key generator's key stream. This technique will generally provide a near-plain mode level of voice quality while containing the encrypted channel to within the plain modes voice channel bandwidth. It is common in the newer 'analog' techniques to digitize the signal, but it processes (in many respects) like an analog signal. In this respect, it is a bit of a minomer to call it 'analog encryption', however it is done primarily to differentiate it from 'digital' voice encryption techniques (see the discussions below).

The analog voice encryptor can be viewed as a hybrid between a digital encryptor and a voice scramber. It also digitizes the voice signal (often at a data rate much higher than the typical VoCoder), but handles the voice processing in a manner that allows digital-to-analog reconstruction in a bandwidth constrained manner. This means that although the analog voice signal is digitally processed, it retains sufficient voice-like chracteristics, that when transmitted out over the channel, maintains the energy within the original voice channel.

source: http://www.tccsecure.com/voicecrp.htm