3.2.1. Using Existing Sound/Video Input

Many computers are built with inputs that digitize some real-world analog source, such as sound from a microphone or video input from a camera. The "input" from a sound digitizer with no source plugged in or from a camera with the lens cap on is essentially thermal noise. If the system has enough gain to detect anything, such input can provide reasonably high quality random bits. This method is extremely dependent on the hardware implementation.

For example, on some UNIX-based systems, one can read from the /dev/audio device with nothing plugged into the microphone jack or with the microphone receiving only low level background noise. Such data is essentially random noise, although it should not be trusted without some checking, in case of hardware failure, and it will have to be de-skewed.

Combining this approach with compression to de-skew (see Section 4), one can generate a huge amount of medium-quality random data with the UNIX-style command line:

cat /dev/audio | compress - >random-bits-file

A detailed examination of this type of randomness source appears in [TURBID].