We are launching our own version of what people call Crash games, made popular by Bustabit, at
https://betking.io We use the same provably fair system as Bustabit.
I'll quote RHavar throughout this post.
Starting with a secret I've generated a chain of 10,000,000 SHA256 hashes. Each element is the hash of the lowercase, hexadecimal string representation of the previous hash.
The hash of the BetKing chain's last element is 863165db9a59e5720b3ea5659313e1f8c0546d3ef113d0959cb076cc79eec244.
Every game maps to a hash in the chain: The 10,000,000th element of the chain is the hash of game #1 and the first element in the chain is the hash of game #10,000,000. To verify that a hash belongs to a game #n, simply hash it n times and compare the result with the terminating hash.
To calculate a game's result from its hash:
const crypto = require("crypto")
function gameResult(seed, salt) {
const nBits = 52 // number of most significant bits to use
// 1. HMAC_SHA256(key=salt, message=seed)
const hmac = crypto.createHmac("sha256", salt)
hmac.update(seed)
seed = hmac.digest("hex")
// 2. r = 52 most significant bits
seed = seed.slice(0, nBits/4)
const r = parseInt(seed, 16)
// 3. X = r / 2^52
let X = r / Math.pow(2, nBits) // uniformly distributed in [0; 1)
// 4. X = 99 / (1-X)
X = 99 / (1 - X)
// 5. return max(trunc(X), 100)
const result = Math.floor(X)
return Math.max(1, result / 100)
}
Before being used to calculate the corresponding result, each game hash is salted with the lowercase, hexadecimal string representation of the hash of a bitcoin block that has not been mined yet, proving that I have not deliberately picked a chain that is unfavorable for players.
The block we will use is
bitcoin block 545340Quoted for future reference. Also archived.