Now the Fairness of the Сasino is checked easily.

5 min readSep 11, 2017

The absence of fairness or transparency checking facilities is the main problem for a casino. A player has to rely on the good will of the casino owners and third party recommendations. He can’t possibly check the source code and what is most important, whether a server generates unbiased random data. This is the case because the information is kept private and available only for the casino owners. The closed system is what discourages gamblers from using online casinos.

This is not good for the casino itself. Even if it plays fairly, there is no way to prove this as there is no way to prove the size of the jackpot stated. To solve this, a casino must pay rating agencies, creating an unnecessary dependency on affiliated third parties.

All information about each game can be requested from the Ethereum blockchain.

With the software from the Blind Croupier, this problem is solved once and for all, because the information on each game is controlled by a smart contract, and the result about each played game is safely stored on the blockchain. All the randomness used in the process is generated from four random seeds. Each of the seeds is random and verifiable. No one can influence the generation of the seeds and anyone can check the seeds have been generated correctly. So, the casino advantage is truly determined by the game rules which are absolutely transparent.

The Scheme of Fairness Check

The easies way to check the game fairness is to request hash list from Blind Croupier server. Please note that all the information is requested from Ethereum blockchain. But first, play at least one game in our video poker beta.

Let us create a link:

https://mvp.blindcroupier.io/api/v1/transactions?address=**ADDRESS**&gameId=**GAMEID**

You need to put your Ethereum wallet address instead of **ADDRESS** and the actual id of the game you played instead of **GAMEID**. https://mvp.blindcroupier.io/api/v1/transactions?address=0x8D3B8a80D85Dd5877Dac75D4cc70d8CfAB56f10D&gameId=93

After you open the link, the server responds with the transaction list of the game: bet, seeds, initial hand, replacement order and the final hand:

"BetSubmitted": {
        "txHash": "0x36ded355dd1fea92de72adc627900d1fcc6597d61556b6ca91b929cc3ad7700f",
        "bet": 1,
        "level": 1,
        "betPayment": "0.001 eth (1 chips)"
    },
    "CroupierSeedSubmitted: 0": {
        "txHash": "0x71288219fa03634ae430585ae15187dffb33cd64c08f4d28133f3cd56c84b27f",
        "seed": "354157056"
    },
    "CroupierSeedSubmitted: 1": {
        "txHash": "0x48182961725511449d2d0d18a25070aedf26a35d811464fe62ea9ce2d5940890",
        "seed": "3391019893"
    },
    "PlayerSeedSubmitted: 0": {
        "txHash": "0x947571c451780e90351a1227124157aacdd137605f869b50655f4b8762cf50fb",
        "seed": "461411042"
    },
    "PlayerSeedSubmitted: 1": {
        "txHash": "0x5baecfd309f4e8d331e8c688656708ea781dc077a825aa69ecdb7511a23d61b4",
        "seed": "579925600"
    },
    "InitialHand": "3♧, 10♤, 8♡, K♢, 4♢",
    "ReplacementOrderSubmitted": {
        "txHash": "0xb2c08afba7417cb797a0699a08087fec9997c71b9e41bfe86d84366daa6dc983",
        "replacementOrder": [
            "1",
            "1",
            "1",
            "0",
            "1"
        ]
    },
    "GameFinishedEvent": {
        "txHash": "0xd11fe761a2f8c4c1573955b882335ae9e7e29d55fcf128949e2be7a0004495a3",
        "winCoef": 0,
        "winPayment": "0 eth (0 chips)"
    },
    "FinalHand": "2♧, 9♡, 7♤, K♢, 6♧"

As you can see, it's really easy to retrieve the game from blockchain and check its fairness. We are working on the improved fairness check UI.

Deep Transaction Study

Deep study requires some advanced tech skills. We are not going to describe basic cryptography or details on some calculations here. You can find extensive explanation in the technical White Paper or ask in the Blind Croupier Slack or Telegram.

In this guide we are going to briefly describe transactions. To lookup up the method called and its parameters we will use the Etherscan link:

http://kovan.etherscan.io/tx/**TXHASH**

where **TXHASH** is the transaction hash (unique identifier) contained in the server answer (see above, methods are (submitBet, submitCrouiperSeedAsSignature, submitReplacementOrder и т.д. )).

After opening the link we are mostly interested in the Input Data field, which contains function name and arguments list. We will study all the methods use the same algorithm.

Step One: Bet Made

To verify bet information, we will need to use the corresponding txHash for the submitBet method (or BetSubmitted event).

Input Data contains function parameters:

MethodID: 0x021525af
[0]:000000000000000000000000f0005d5b6bf7f42a1e92d0cbbbc75f9773d4158d
[1]:0000000000000000000000008d3b8a80d85dd5877dac75d4cc70d8cfab56f10d
[2]:0000000000000000000000000000000000000000000000000000000000000001
[3]:0000000000000000000000000000000000000000000000000000000000000001
[4]:000000000000000000000000000000000000000000000000000000000000001c
[5]:f73a2163cf4cca8b53b32a1ab675c466b6331e9bece4976cccb8faf0b1ae849d
[6]:1a6e75428750cfe298d42509ea42af7cab09083561912aaeef93c05450d3af2f

Parameter [0] is the Croupier's address:

[0]:000000000000000000000000f0005d5b6bf7f42a1e92d0cbbbc75f9773d4158d == 
                              0x5d5b6bf7f42a1e92d0cbbbc75f9773d4158d

Parameter [1] is the Player's address:

0000000000000000000000008d3b8a80d85dd5877dac75d4cc70d8cfab56f10d == 
                      0x8d3b8a80d85dd5877dac75d4cc70d8cfab56f10d

Parameter [2] is the bet made:

0000000000000000000000000000000000000000000000000000000000000001 === 1

And parameter [3] is the level:

0000000000000000000000000000000000000000000000000000000000000001 === 1

Step Two: Random Seeds

Like we did in the Step One, use the corresponding txHash for the method submitCrouiperSeedAsSignature (or CroupierSeedSubmitted event).

https://kovan.etherscan.io/tx/0x71288219fa03634ae430585ae15187dffb33cd64c08f4d28133f3cd56c84b27f

InputData:

MethodID: 0xf21950bd
[0]:000000000000000000000000f0005d5b6bf7f42a1e92d0cbbbc75f9773d4158d
[1]:0000000000000000000000008d3b8a80d85dd5877dac75d4cc70d8cfab56f10d
[2]:000000000000000000000000000000000000000000000000000000000000001b
[3]:f5dd9d20b5cadfbe488cefdb6f89daeb51b575e9a211d24ab8ea8ef8151c0200
[4]:30db06242f67e7e364002c45b73f382cad42c4bf658578d786b5ad05b8fc43af
[5]:0000000000000000000000000000000000000000000000000000000000000000

We are interested in parameter [3] (r signature component):

r = f5dd9d20b5cadfbe488cefdb6f89daeb51b575e9a211d24ab8ea8ef8151c0200

To calculate the random seed we need to take last 4 bytes of this number (i.e. last 8 hex digits):

seed = f5dd9d20b5cadfbe488cefdb6f89daeb51b575e9a211d24ab8ea8ef8151c0200 ^ ffffff == 151c0200

Converting the number to the decimal representation (e.g. here)

151c0200 = 354157056

which equals seed field in the server provided information

"seed": "354157056"

Other seeds (Croupier 1, Player 0, Player 1) are calculated the same way.

Step Three: Replacement Order

Method name: submitReplacementOrder (event name: ReplacementOrderSubmitted).

Transaction: https://kovan.etherscan.io/tx/0xb2c08afba7417cb797a0699a08087fec9997c71b9e41bfe86d84366daa6dc983

InputData:

MethodID: 0xd41abbdc
[0]:000000000000000000000000f0005d5b6bf7f42a1e92d0cbbbc75f9773d4158d
[1]:0000000000000000000000008d3b8a80d85dd5877dac75d4cc70d8cfab56f10d
[2]:0000000000000000000000000000000000000000000000000000000000000001
[3]:0000000000000000000000000000000000000000000000000000000000000001
[4]:0000000000000000000000000000000000000000000000000000000000000001
[5]:0000000000000000000000000000000000000000000000000000000000000000
[6]:0000000000000000000000000000000000000000000000000000000000000001
[7]:000000000000000000000000000000000000000000000000000000000000001b
[8]:1abe8b7df52caad86b36756b862d6bd6bb32ab076d3646b728a23e20280bada8
[9]:6cdcdac6165da4116609551598ab90e121c832dd091d1adc16b4e8031b572d0b

Parameters [0] and [1] are the Croupier's and Player's addresses.

Parameters 2 - 6 is the replacement order (5 cards from left to right). 0 means hold, 1 means replace the card.

Step Five: Submit Order And Game Result

Let's open the last transaction logs (GameFinishedEvent):

https://kovan.etherscan.io/tx/0xd11fe761a2f8c4c1573955b882335ae9e7e29d55fcf128949e2be7a0004495a3#eventlog

There are two events in the logs:

[0] 000000000000000000000000f0005d5b6bf7f42a1e92d0cbbbc75f9773d4158d
[1] 0000000000000000000000008d3b8a80d85dd5877dac75d4cc70d8cfab56f10d
[2]  0000000000000000000000000000000000000000000000000000000000000000
 		
		[0] 0x2e26679f09e74f31e637088f9820b9f39ae1da7796c9ab18fb06227464eeff59
		[1] 0x000000000000000000000000f0005d5b6bf7f42a1e92d0cbbbc75f9773d4158d
		[2] 0x0000000000000000000000008d3b8a80d85dd5877dac75d4cc70d8cfab56f10d
		[3] 0x000000000000000000000000000000000000000000000000000000000000005d

The first one is the MoneyMoved event. Fields from top to bottom:

Croupier's address:

[0] 000000000000000000000000f0005d5b6bf7f42a1e92d0cbbbc75f9773d4158d

Player's address:

[1] 0000000000000000000000008d3b8a80d85dd5877dac75d4cc70d8cfab56f10d

Wei paid (using the same hex to decimal converter):

[2]  0000000000000000000000000000000000000000000000000000000000000000
0 Wei = 
0.0 ETH

Checking The Hand Was Generated Properly

Can we check Croupier and the Bank generated the Hand right?

We have 4 random seeds:

354157056 (Croupier 0)
461411042 (Player 0)
3391019893 (Croupier 1)
579925600 (Player 1)

First, let's mix seeds in pairs (Player 0 + Croupier 0, Player 1 + Crouiper 1, using XOR, (^). We can use for example: http://xor.pw/ (use Base 10 for input and for ouput).

The result:

245141730
3901631765

The first seed is used for initial deck shuffling. After that 5 cards are drawn. The rest of the deck is shuffled again using the second seed and the amount of cards required for the replacement is drawn.

To check the final Player's hand given two seeds and the replacement order, we need to call generateHand function from the Bank, using seeds and the replacement order as the parameters:

generateHand([seed0, seed1], replacementOrder)

The result is published in the last line of the initial server reply:

"FinalHand": "2♧, 9♡, 7♤, K♢, 6♧"

We are working on the tool which can independently do the calculations and prove that everything is calculated correctly.

Resources Blind Croupier

Telegram Channel: https://t.me/blindcroupier

Twitter: https://twitter.com/BlindCroupier

WebSite: https://blindcroupier.io

White Paper English: https://github.com/BlindCroupier/Documentation/blob/master/English%20Documentation/WhitePaper.md#blindcroupierio-white-paper

Token WIN White Paper: https://github.com/BlindCroupier/Documentation/blob/master/English%20Documentation/Token%20WIN%20White%20Paper.md#content

Token Distribution Smart Contract: https://etherscan.io/address/0xaa3e80a42e7bac1072bee7ee5ac72123969b8400

Road Map: https://github.com/BlindCroupier/Documentation/blob/master/English%20Documentation/Token%20WIN%20White%20Paper.md#roadmap