RNG/DRBG/PRNG Cheat Sheet

• RNG (Random Number Generator) produces random bits
• non-deterministic
• uses external analog source
• DRBG (Deterministic Random Bit Generator) produces pseudorandom bits
• deterministic
• from a seed (taken from RNG)
• PRNG (Pseudo-Random Number Generator) produces pseudorandom bits
• non-deterministic
• from a seeds from an RNG to maintain entropy pool
• produces output bits using a DRBG

Analog Source + seed --> RNG --> 010..10 --> PRNG (DRBG is a component of PRNG) --> 0101011100..01 

Deterministic Random Bit Generator, DRBG
INPUT: short fixed-length seed (e.g. 256 bit)
OUTPUT: arbitrarily long

Bad, do not use	Good, do use
rand(3)	/dev/urandom
random(3)	Linux getrandom()
PHP rand()	Java SecureRandom
your own algorithm	Node.js crypto.randomBytes
&nbrp;	WINAPI BCryptGenRandom
&nbrp;	openssl rand