Chopper (radio technology)
Chopper is an internal name for previously used analog encryption techniques , such as those used by the security authorities ( BOS ) and secret services in radio communication . Earlier technologies (before the time of digital technology ) chopped up speech into small segments, which were distributed into different frequency ranges with a ring modulator , which made the speech almost incomprehensible to a listener.
There was a concealment addition to the analog German authorities radio BOS radio . Through this the speech signals were only mirrored (inverted). This made them incomprehensible in a normal receiver, but fragments of conversation could still be guessed at. With knowledge of the correct image frequency, the complete signal could be restored.
The manufacturer Motorola supplied additional boards for encryption (so-called option boards ) for its handheld radios . Of these, the following used patented, proprietary standards:
- DVP, Digital Voice Protection
- DVP-XL, as above, extended key space
- DVI, Digital Voice International, approved for export (smaller key space)
There were also these boards for open US government standards:
- DES, Data Encryption Standard
- DES-XL, as above, extended key space
Before use, the radios must be charged with a current daily key . To do this, all devices in a task force must be connected to a KVL (Key Variable Loader) by cable. In order to simplify this procedure, the OTAR ( Over The Air Rekeying ) process was invented, whereby the daily key is transmitted by radio.