HMAC

HMAC (Hash-based Message Authentication Code) is a cryptographic algorithm that combines a secret key with a hashing function to produce a tamper-proof verification code, used in crash games to prove that round outcomes were predetermined and not manipulated after bets are placed.

In provably fair crash games, the casino generates a server seed before a round begins and combines it with a client seed and a nonce using HMAC — typically HMAC-SHA256. The resulting hash determines the crash multiplier. Because the hash is published before the round and the underlying seeds are revealed afterward, any player can independently recalculate the result and confirm it matches. If even a single character in the input changes, the output hash changes completely, making silent manipulation mathematically detectable.

Here is a simplified example of how HMAC protects a result: suppose the server seed is abc123, the client seed is xyz789, and the nonce is 1. The casino feeds these three values into HMAC-SHA256 and gets a fixed output hash. That hash is converted into the crash point — say, 3.41×. After the round, you can paste those exact seeds into any HMAC-SHA256 calculator and verify you get the same hash and the same multiplier. No other input combination produces that output, so the casino cannot retroactively change when the game crashed.

Pigaboom is one example of a provably fair crash game that publishes its HMAC verification method openly, allowing players to audit every round using standard cryptographic tools available online.

One practical caveat: HMAC verification only works if you actually check it. Most players never do, which means the fairness guarantee exists but goes unused. To get real value from provably fair systems, bookmark a SHA256 HMAC calculator and spot-check rounds periodically — especially after unusually low crash points.

See also: Provably Fair Crash Games Explained