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How to make tough scrambling?

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Newbie level 6
Dec 23, 2005
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i wanna ask about the more effective scrambling methods in a Tx Rx link. I dont know anything about scrambling or encryption.

anyone has recommendations ?

In radio terminology "scrambling" somtimes means a systems to make the number
of 1's and the number of 0's aproximatley equal.

I take it you want to make it as hard for someone to receive the data passing
between your transmitter and receiver?

Wikipedia article on encryption.

I like the book "applied crytography" by Bruce Schneider

On a radio link you have to allow for some data gettting lost.
If you have a two way radio link you can detect packet loss and resend data,
you can use block encryption or stream encryption.
One a one way link you have to use block encryption so you can cope with some
block being lost.

With a two way radio link you can use public key cryptography where the two nodes
generate a key when they start talking to each other or both ends can have a key
in permanent memory read to use. Generating a public key tends to be
processor intensive.

If you have a one way link then you have to use a symetric algorithm and
install a key in both units before they can communicate.

If you want to prevent a unauthorised transmitter talking to your receiver
then thats a slightly different problem.

For high security it's best to use a well known algorithm since encryption
algorthims made by engineers and programmers tend to have problems that
are only obvious to crytography experts.

You need to consider your threat model. Are you trying to protect
against a radio enthusiast with a scanner from radio shack, an adversary
with money and expertise, the USA national security agency?
How valuable is the information you are protecting?

You need to balance security against the amount of memory and processing
power you need.


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