May 26, 2018
Cryptographically Secure, True Random Number Generator
CryptRandom is an interface module to the /dev/random device found on most modern Unix systems. The /dev/random driver gathers environmental noise from various non-deterministic sources including inter-keyboard timings and inter-interrupt timings that occur within the operating system environment.
The /dev/random driver maintains an estimate of true randomness in the pool and decreases it every time random strings are requested for use. When the estimate goes down to zero, the routine blocks and waits for the occurrence of non-deterministic events to refresh the pool.
The /dev/random kernel module also provides another interface, /dev/urandom, that does not wait for the entropy-pool to recharge and returns as many bytes as requested. /dev/urandom is considerably faster at generation compared to /dev/random, which should be used only when very high quality randomness is desired.