What Is a Random Number Generator?

A Random Number Generator (RNG) is the algorithmic engine that determines outcomes in online casino games — from which symbol lands on a slot reel to which card is dealt in a virtual blackjack hand. Without certified RNG technology, no online casino can credibly claim its games are fair. Understanding how RNGs work is valuable for operators evaluating game studios, developers building platforms, and players who want to understand what "certified fair" actually means.

Two Types of RNG: PRNG vs. TRNG

Pseudo-Random Number Generators (PRNGs)

The overwhelming majority of online casino games use PRNGs — algorithms that generate sequences of numbers that appear statistically random but are actually produced by a deterministic mathematical formula seeded with an initial value. The most widely used PRNG in iGaming contexts is the Mersenne Twister algorithm, valued for its extremely long period and strong statistical properties.

Key characteristics of PRNGs in iGaming:

  • The seed value is typically derived from system entropy sources (hardware timers, OS entropy pools) to ensure unpredictability
  • New seeds are generated continuously — often thousands of times per second — regardless of whether a player is actively spinning or betting
  • The output sequence is statistically tested against industry standards such as NIST SP 800-22 before certification

True Random Number Generators (TRNGs)

TRNGs derive randomness from physical phenomena — thermal noise, atmospheric noise, or radioactive decay. While theoretically "more random" than PRNGs, TRNGs are rarely used in online casino games in practice because they are slower to generate numbers and offer no meaningful advantage for game fairness when properly implemented PRNGs are used instead.

How Outcomes Are Mapped from Numbers to Game Results

The RNG produces a raw number within a defined range. A mapping function then translates that number into a game outcome:

  1. The RNG generates a number, e.g., between 0 and 4,294,967,295 (for a 32-bit generator).
  2. This number is divided into outcome buckets corresponding to each possible game result and its intended probability weight.
  3. The bucket the number falls into determines the displayed outcome — a specific symbol combination, card value, or roulette number.
  4. The weighting of these buckets is what determines a game's Return to Player (RTP) percentage.

RNG Certification: What It Means and Who Does It

A certified RNG has been independently tested by an accredited laboratory to verify that its output meets statistical randomness standards and that game outcomes match the declared probability distributions. Major testing houses include:

  • eCOGRA — UK-based; widely recognized across European regulated markets
  • BMM Testlabs — global footprint; recognized in numerous jurisdictions
  • iTech Labs — Australian-founded; recognized in many Asia-Pacific and European markets
  • GLI (Gaming Laboratories International) — one of the largest global gaming test labs

Certification is not a one-time event. Certified RNGs must be re-tested whenever the underlying algorithm is modified, and many jurisdictions require periodic re-certification regardless of changes.

Provably Fair: Blockchain-Based Verification

Some crypto-native casinos implement "provably fair" systems using cryptographic hashing, allowing players to independently verify that game outcomes were not manipulated after bets were placed. The mechanism typically works as follows:

  1. Before the game round, the server generates and hashes a server seed, sharing the hash (but not the seed itself) with the player.
  2. The player contributes a client seed.
  3. After the round, both seeds are revealed and combined to derive the outcome, which any player can verify independently.

While provably fair systems are transparent by design, they are not yet accepted as equivalent to traditional RNG certification under most regulatory frameworks.

Takeaways for Operators

When evaluating game studios or building your own game content, always verify RNG certification status and understand which jurisdictions that certification is recognized in. A game certified by one testing house may not meet the requirements of every regulatory authority where you intend to operate.