The document describes Linux's random number generator which collects entropy from various sources and stores it in an entropy pool to provide random numbers. The entropy sources include hardware generators, user input, device I/O, timers, and third party daemons. The entropy is collected in the kernel space entropy pool and can then be read from /dev/random and /dev/urandom by applications in user space.

1. LINUX RANDOM NUMBER
GENERATOR
2016/3/28

2. Linux Random Number
Generator
Entropy Source
Entropy Pool (random.c)
input_pool
nonblocking_pool blocking_pool
add_input_randomness() add_hwgenerator_randomness()
add_timer_randomness()
add_device_randomness()
/dev/random/dev/urandom
Interrupt
Requests
Human
Input
Device I/O
HW RNG
(hw_random.c)
Application
Read Read
3rd
party entropy
generator Daemon
(like rngd, haveged)
Write Write
User
space
Kernel
space
Get

3. Reference
 Ensuring Randomness with Linux's Random
Number Generator
 https://blog.cloudflare.com/ensuring-
randomness-with-linuxs-random-number-
generator/
 The Linux Random Number Generator
 https://pthree.org/2014/07/21/the-linux-random-
number-generator/