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Scrambler

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Electrix

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Hi
Could someone please explain how "scrambling" in digital communication works ? In particular what is the theory behind Tapped Shift Register in achiveing scrambling of data.

ALso if you could provide me Links to websites offering info on this


Thanks.
 
A shift register with feedback generates a "pseudo random" bit sequence.
This is fed to one input of an XOR and the data to be encrypted fed to the other.
The output of the XOR is the encypted stream.

At the receiving end an identical pseudo random sequence and the encrypted information are fed to another XOR. The output will be the recovered original data.
 
When you tap a shift register, instead of taking bit 1 as bit 1 it is changed for bit 5 for example, and so on. There are many methods but wireing your ADC to your PISO register through a switch array is the most common, and easiest. Then on the other side you wire up your SIPO register to the DAC in the oposite way.

Scrambling is not a very good way of encrypting data though, it can be pseudo cracked by brute force, and completely or effecively cracked just by listening or using an oscilloscope.
 
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