kb/data/developer.mozilla.org/en-US/docs/Glossary/RNG-0.md

title	chunk	source	category	tags	date_saved	instance
Random Number Generator - Glossary | MDN	1/3	https://developer.mozilla.org/en-US/docs/Glossary/RNG	reference	web, html, css, javascript, documentation	2026-05-05T05:41:56.298429+00:00	kb-cron

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1. Glossary
2. Random Number Generator

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.

In this article

• See also

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