Cryptography Reference
In-Depth Information
than
m
, then we don't use it and generate another number instead. Consequently,
in what follows we only elaborate on the generation of random bits, and we
consider the construction of random numbers from random bits to be simple and
straightforward.
According to the leading quote of this chapter, random numbers (and random
bits) should not be generated with a method chosen at random, and hence the
question of how to actually generate random bits arises immediately. This question
is addressed next.
9.2
REALIZATIONS AND IMPLEMENTATIONS
In informational RFC 1750 [2], it is recommended that special hardware is used to
generate truly random bits. There are, however, also some situations in which special
hardware is not available, and software must be used to generate random bits instead.
Consequently, there is room for both hardware-based and software-based random bit
generators. Some general ideas about how to realize and implement such generators
are overviewed next. Afterwards, the notion of deskewing techniques is introduced
and very briefly explained.
9.2.1
Hardware-Based Random Bit Generators
Hardware-based random bit generators exploit the randomness that occurs in phys-
ical processes and phenomena. According to [3], examples of such processes and
phenomena include:
•
The elapsed time between emission of particles during radioactive decay;
•
The thermal noise from a semiconductor diode or resistor;
•
The frequency instability of a free-running oscillator (e.g., [4]);
•
The amount a metal insulator semiconductor capacitor is charged during a
fixed period of time (e.g., [5]);
•
The air turbulence within a sealed disk drive that causes random fluctuations
in disk drive sector read latency times (e.g., [6, 7]);
•
The sound from a microphone or video input from a camera.
It goes without saying that other physical processes and phenomena may be
employed by hardware-based random bit generators.
Hardware-based random bit generators could be easily integrated into contem-
porary computer systems. This is not yet the case, and hardware-based random bit
