pwarren/rtl-entropy

What's the samplerate for?

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webernetz commented

Hello Paul,

I have a question concerning the samplerate (-s ). What exactly does it? When I am running your program with the default value nothing passes the FIPS tests. But when I decrease the value to "-s 2.4M" I get much random data.
I am confused because to my mind the samplerate is the speed of reading out the data from the stick which should not change the entropy, isn't it?

Thanks a lot!
Johannes

pwarren commented

So the -s parameter of rtl_entropy exposes the samplerate parameter of the underlying rtl-sdr library. It correlates with the bandwidth of the sampled RF. So a 2MHz sample rate gives you data from your centre frequency -1 and +1 MHz. Lower sample rates use less CPU to turn that RF stream in to useful entropy. Pretty much any x86 computer that can still run Chrome shoudl be easily able to cope with the full 3MHz bandwidth, raspberry pi and other similar devices might struggle at that rate.

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kovacs-andras commented

Better late than never. :D Thanks!

Remmy commented

Unless I am misunderstanding, I don't yet see how this explains the failing FIPS tests?