Random Number Generator

A PRNG (pseudorandom number generator) is an algorithm that outputs numbers in a complex, seemingly unpredictable pattern. Truly random numbers (say, from a radioactive source) are utterly unpredictable, whereas all algorithms are predictable, and a PRNG returns the same numbers when passed the same starting parameters or seed.

PRNGs can be used for a variety of applications, such as games.

A cryptographically secure PRNG is a PRNG with certain extra properties making it suitable for use in cryptography. These include:

• that it's computationally unfeasible for an attacker (without knowledge of the seed) to predict its output
• that if an attacker can work out its current state, this should not enable the attacker to work out previously emitted numbers.

Most PRNGs are not cryptographically secure.

See also

• JavaScript's Math.random() and CSS's random() built-in PRNG functions. Note that these are not a cryptographically secure PRNG.
• Crypto.getRandomValues(): this is intended to provide cryptographically secure numbers.
• Pseudorandom number generator on Wikipedia