# "Provably Fair"

## On Game Theory with Bitcoins

### What exactly does Provably Fair mean?

Provably Fair was a new revolution in fair game play accountability introduced with the dawn of Bitcoin. These gambling sites allow the public to see how outcomes are based on the gambler's input and a secret number that is disclosed and changed for the next rounds every hour for example. This allows online gamblers to verify if the website "played" fair.

BitLotto was likely the first blockchain based "provably fair". It uses the transaction ID as the "ticket", and the results of a large government-run lottery to determine the winning numbers.

SatoshiDICE (now rebranded as MegaDice became a blockbuster blockchain method for online gambling. It uses the transaction ID to determine the "lucky number" (between 0 and 65,535). The secret used for determining that lucky number is revealed after the end of the day.

### Theory of winning at provably fair games

There is no such thing as TRUE randomness

Provided enough data, patterns arise in seeming random events, even in nature

The idea behind actually beating the house requires that you first heuristically memorize the game flow.

This is evident in games like Baccarat, where you can notice patterns in the gameplay and use that to your advantage, by increasing or decreasing your bets at the most probably fair time.

# Source Code

This site invites you to examine the Javascript running the game!

Good example code, do a GitHub Search for provablyfair.

https://github.com/Quartzic/Hashly/blob/master/js/verify.js

## Simple Javascript Example

### SHA-256 function

Written by

``` function SHA256(s){ var chrsz = 8; var hexcase = 0; function safe_add (x, y) { var lsw = (x & 0xFFFF) + (y & 0xFFFF); var msw = (x >> 16) + (y >> 16) + (lsw >> 16); return (msw << 16) | (lsw & 0xFFFF); } function S (X, n) { return ( X >>> n ) | (X << (32 - n)); } function R (X, n) { return ( X >>> n ); } function Ch(x, y, z) { return ((x & y) ^ ((~x) & z)); } function Maj(x, y, z) { return ((x & y) ^ (x & z) ^ (y & z)); } function Sigma0256(x) { return (S(x, 2) ^ S(x, 13) ^ S(x, 22)); } function Sigma1256(x) { return (S(x, 6) ^ S(x, 11) ^ S(x, 25)); } function Gamma0256(x) { return (S(x, 7) ^ S(x, 18) ^ R(x, 3)); } function Gamma1256(x) { return (S(x, 17) ^ S(x, 19) ^ R(x, 10)); } function core_sha256 (m, l) { var K = [0x428A2F98, 0x71374491, 0xB5C0FBCF, 0xE9B5DBA5, 0x3956C25B, 0x59F111F1, 0x923F82A4, 0xAB1C5ED5, 0xD807AA98, 0x12835B01, 0x243185BE, 0x550C7DC3, 0x72BE5D74, 0x80DEB1FE, 0x9BDC06A7, 0xC19BF174, 0xE49B69C1, 0xEFBE4786, 0xFC19DC6, 0x240CA1CC, 0x2DE92C6F, 0x4A7484AA, 0x5CB0A9DC, 0x76F988DA, 0x983E5152, 0xA831C66D, 0xB00327C8, 0xBF597FC7, 0xC6E00BF3, 0xD5A79147, 0x6CA6351, 0x14292967, 0x27B70A85, 0x2E1B2138, 0x4D2C6DFC, 0x53380D13, 0x650A7354, 0x766A0ABB, 0x81C2C92E, 0x92722C85, 0xA2BFE8A1, 0xA81A664B, 0xC24B8B70, 0xC76C51A3, 0xD192E819, 0xD6990624, 0xF40E3585, 0x106AA070, 0x19A4C116, 0x1E376C08, 0x2748774C, 0x34B0BCB5, 0x391C0CB3, 0x4ED8AA4A, 0x5B9CCA4F, 0x682E6FF3, 0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208, 0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2]; var HASH = [0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A, 0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19]; var W = new Array(64); var a, b, c, d, e, f, g, h, i, j; var T1, T2; m[l >> 5] |= 0x80 << (24 - l % 32); m[((l + 64 >> 9) << 4) + 15] = l; for ( var i = 0; i>5] |= (str.charCodeAt(i / chrsz) & mask) << (24 - i%32); } return bin; } function Utf8Encode(string) { string = string.replace(/\r\n/g,"\n"); var utftext = ""; for (var n = 0; n < string.length; n++) { var c = string.charCodeAt(n); if (c < 128) { utftext += String.fromCharCode(c); } else if((c > 127) && (c < 2048)) { utftext += String.fromCharCode((c >> 6) | 192); utftext += String.fromCharCode((c & 63) | 128); } else { utftext += String.fromCharCode((c >> 12) | 224); utftext += String.fromCharCode(((c >> 6) & 63) | 128); utftext += String.fromCharCode((c & 63) | 128); } } return utftext; } function binb2hex (binarray) { var hex_tab = hexcase ? "0123456789ABCDEF" : "0123456789abcdef"; var str = ""; for(var i = 0; i < binarray.length * 4; i++) { str += hex_tab.charAt((binarray[i>>2] >> ((3 - i%4)*8+4)) & 0xF) + hex_tab.charAt((binarray[i>>2] >> ((3 - i%4)*8 )) & 0xF); } return str; } s = Utf8Encode(s); return binb2hex(core_sha256(str2binb(s), s.length * chrsz)); } function updateHashes() { console.log("Updating hashes!"); var shortcode = document.getElementById('shortcode'), longcode = document.getElementById('longcode'), number = document.getElementById('number'), salt = document.getElementById('salt'); salt.value = salt.value.toLowerCase(); number.value = number.value.substring(0,4); var tohash = ""; var hashresult = ""; tohash = number.value + salt.value; hashresult = SHA256(tohash); shortcode.innerHTML = hashresult.substring(0,12); longcode.innerHTML = hashresult.substring(0,48); } ```