When a government official wants to make a confidential telephone call to, say, an embassy abroad he uses a voice scrambler. As the conversation travels between the two telephones it is nothing but incomprehensible noise to anyone ‘trapping’ into the line.
Most scramblers are electronic ciphering machines that invert the high and low tones of a human voice to make it unintelligible. Other scramblers conceal the voice in a background of continuous noise.
At one time scramblers were issued only to senior military commanders who had to exchange sensitive information over telephone lines that might be listened into by the enemy. Now scramblers have become more easily available, and are often used by international businessmen anxious to protect trade secrets from unscrupulous competitors. Modern technology has reduced their size so they fit into a briefcase.
Double unit
Scrambling requires two units, the transmitter and the receiver. The transmitter converts the caller’s speech into the unintelligible form and sends it down a normal telephone line. The receiver reverses the process so that the voice can be understood at the other end. Eavesdroppers tapping into the line will hear a highly distorted, synthetic noise that is hardly recognizable as human speech.
Most scramblers work by splitting the sound of the voice into five frequency bands which are then mixed through a complicated electronic process which moves and inverts them. In theory there are about 3840 possible combinations, but standard scramblers use 512 permutations.
Voice scramblers are not a complete safeguard against skilled eavesdroppers, as conversations can eventually be unscrambled. But the process is extremely time-consuming, requiring the use of specially programmed data processors and highly trained operators, so scramblers do give short-term protection.
In the early 1960s, the US Embassy in Moscow managed to pick up the scrambled conversations passing between the Politburo’s fleet of limousines. Although there was a long delay before the signals could be unscrambled, the exchanges contained some extremely useful political information – and quite a bit of Kremlin gossip. The operation eventually ended when new security measures were introduced.
Picture Credit : Google