Python Random Number Generator for OTP

[Bill Stewart]

> > >Â  Why not use /dev/random, instead of "ensuring you have entropy"Â

> > /dev/random limits the output size to the 
> estimated entropy. So it has abysmal 
> performance unless there are high performance entropy sources available.

This is for a one-time pad.  Limiting the output 
size to the estimated entropy is a 
*requirement*.  Abysmal performance is fine, 
because you're going to transfer the pad using a 
briefcase handcuffed to a courier's arm or some 
similarly high-cost high-latency physical 
distribution method, though if you've got a 
higher-performance entropy source, great.

>  After the initial seeding this gains very little security in practice.

If "gains very little security in practice" is 
good enough for you, you don't need a one-time 
pad.  Yes, the pseudo-random bits you get out of 
/dev/urandom will probably be much better than 
the bits the Russians got by mashing down the 
keys on typewriters, and you're probably not 
going to be attacked with the persistence of the 
Venona decrypters, but don't waste your time 
using one-time pads unless you're going to use 
them perfectly.  You're much better off using a 
long-enough RSA key and some Diffie-Hellman 
session key generation.  (Of course, you still 
want good random numbers for those, but 
/dev/random is plenty fast enough for that, at 
least on any non-virtual machine.)