[Cryptography] randomness +- entropy

[Bill Stewart]

At 01:01 PM 11/8/2013, David Johnston wrote:
>On 11/7/2013 11:08 AM, Jerry Leichter wrote:
>>The smartphone and the embedded system are *very* different.  Any 
>>phone has a microphone and a radio.  Unfortunately, the radios are 
>>usually sealed off so you couldn't use them as a source of radio 
>>noise; but the microphones are wide open.
>I disagree about the 'sealed-off' thing.

Most smartphones have wifi, and can tell you things like signal 
strength and noise levels on different channels, even if they don't 
show you the cellular signals.  It's probably not a rapidly-changing 
signal, but it's going to have some entropy (and if there's not 
enough noise, go microwave some coffee.)  There's also typically an 
accelerometer, and even dumb phones almost all have cameras.

But unfortunately, that $29 cable modem or dsl router isn't going to 
have any spare hardware, even a 5-cent photocell, so it's network 
noise only unless there's wifi.