Alice and Bob share a common time series signal.
1. What can be the largest possible secret key?
2. Will the entropy and secrecy of system depends on this length?
Ideally if after passing though analog to digital converter(ADC) number of bits a signal gives depends on $N_S$ sampling rate. Suppose I had s 1 second window of signal. Through ADC I got $N_S$ samples. I apply threshold on these samples and generate keys. Maximum length hence is $N_S$ bits of secret keys.
Is this the best key? I mean is there any relation between entropy/secrecy of the key vs length I choose from $N_S$?