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EtherJack.io is the first fully smart contract based jackpot game. The core game
process is safe and secure, running completely on-chain, operated by contracts
with disclosed source code, with only optional extensions basing off-chain.
In EtherJack, the whole game process is controlled by participants, in this sense
it’s a massively multiplayer community game.
The rules are simple: bids fill up the jackpot, the last to bid wins and gets the
The developers (or anyone else) can’t affect the game process, can’t manipulate or
adjust it, or change the rules on the fly. The fixed contract code ensures the game
is transparent and fair to all participants.
Smart Contracts in Online Gambling
The advantages of Blockchain systems are apparent when it comes to entrusting
currency to some medium. The medium being a smart contract on a blockchain, for
which the source code is disclosed, and which allows no backdoors for developers,
completely solves the trust issue...
Smart Contracts in Online Gambling
This has lead to a situation where on-chain gambling is something everyone is
talking about, but actually most people keep playing old-fashioned off-chain
games, being susceptible to all the same dirty tricks like rigged RNGs and more.
The problem is likely to be resolved in the future when blockchains become faster
and most transactions are included in blocks and confirmed within a few seconds,
but not today.
EtherJack offers a game, for which quick transaction processing is not critical, and
which is latency tolerant. The game is designed in such a way that the presence
of the latency does neither break the game nor make it less interactive or
Thus, EtherJack enjoys all the advantages of an on-chain game (100% fair and
transparent, with clearly defined and unchangeable rules) and doesn’t suffer from
the downsides associated with slow processing speeds.
One Time Offer and One Time Chance
Unlike many ICOs, the EtherJack ICO is not ...
The basic rules are quite simple. There’s a jackpot, at every moment it’s claimed by
a player (the last to bid), and there’s a countdown timer running. If someone bids
(by sending an amount of Ether to the Jackpot smart contract), that person now
claims the jackpot, the bid is added to the jackpot, and the timer is reset.
If nobody claims the jackpot by the moment the timer runs out, it goes to the last
person who placed a bid. Over time, the bid price goes up (from 0.005 ETH, up to
over 1 ETH), and timer duration goes down (from 3 hours down to 5 minutes).
There’s a second level meta-game present: each 20th, 50th, and 100th bid also win
“minor prizes”: 10% of bids’ worth during the corresponding period. For example,
each 20th bid wins 10% of Ether used for last 20 bids. If all of these bids were
made in Ether, and the bid price didn’t change, it will be precisely double the bid
price. If some of the bids were made in JACK, the amount will be smaller. If the
When the game is running, the bid price changes over time. The bid price depends
on the total amount of bids made, and is defined by the following formula:
Bid amount formula (in wei).
uint256 newBetAmount = 10 finney + (totalBets / 100) * 6 finney;
Bid amount rule. Solidity code present in the Jackpot contract.
Since during the game JACK is purchased or sold at this price, and 1 JACK can
replace this amount of Ether in a bid, this price naturally corresponds to the JACK
intrinsic value during the game stage.
Price at selected points is listed in the table below.
Table. Bid price during the game stage
Bidding an amount of Ether exceeding the bid price at least twice returns ...
The timeout duration after each bid changes over time and depends on the total
amount of bids made. It is defined by the following formula:
Timeout duration formula.
(5 + 19200 / (100 + totalBets)) * 1 minutes
Timeout duration rule. Solidity code present in the Jackpot contract.
The duration at selected points is listed in the table below.
Table. Timeout duration
Bidding an amount of Ether exceeding the bid price at least twice returns JACK
token or tokens to the player (provided there’s supply of JACK available for sale).
See “JACK Token Economy” for details.
Every participant can post messages on the game’s website, for self-advertising,
or for fun.
Posting a message is accomplis...
The confirmation stage also associates the message with a specific Ethereum
address (from where the bid was made) and its total sum of of invested Ether.
The more Ether the poster has invested into the game (across both the ICO and
game stage), the higher their message will be ranked in the Top Messages
section. The “investment weight” is counted just by amount of Ether sent into the
game, not by amount of JACK held or stored in the Vault.
The Last Messages section simply lists the latest messages in the order or their
A player can edit a previously published message by posting a new one and
confirming it from the same Ethereum account or wallet. The message will retain
all weight it has from the invested Ether. Messages can be edited at any time and
at any rate.
The game has four primary components:
JACK Token smart contract
deployed at address 0xe64d5f33E28387855d33980719f27f0d579392aF
Token Smart Contract
The Token smart contract:
Defines the JACK Token and its transfer functions
Handles deposits and withdrawals (intercepts transfers to Croupier and
applies custom logic)
Handles token bids (intercepts transfers to Jackpot and applies custom logic)
Handles deposit freezing and unfreezing (API available for Croupier only) for
token sales through the Jackpot contract
There’s fixed supply of 1 million JACK, which can only decrease. Each time a token
is used for a bet, it’s burned irreversibly, thus decreasing the total supply.
JACK Tokens can be freely transferred between players or traded at exchanges.
When Tokens are sent to Croupier, they are counted towards the user’s deposit
with Croupier on-chain. Later, the entire deposit can be withdrawn, on-chain using
the deposit data stored in the blockchain.
If a deposit owner wants to be selling tokens through the Jackpot contr...
All critical parts of the game are implemented in this smart contract and happen
on-chain. This includes tracking bids, last bidder, keeping the jackpot, checking
game end conditions, paying out the jackpot.
The smart contract interacts with other parts of the system (Token Contract,
Croupier, the website) via method calls and events.
Communication with players is done solely by accepting and emitting transfers
(JACK and Ether).
Actions on incoming Ether transfer depend on the stage:
transfer bought JACK to the investors
accept Ether as a bid, if it’s double bid price or more, sell JACK;
accept JACK as a bid
if the jackpot hasn’t been paid out yet, and there’s an incoming
transfer for any amount from the winner, transfer the jackpot to the winner.
This operation is not really needed, since Croupier will automatically make Jackpot
perform the payment when it det...
Start of development.
Security tests and audit
Demo mode launched on the game website
Kickstart-ICO started. Aim is to collect 333 ETH to form a jackpot
ICO completed and the game starts
1,000 bids made.
1 JACK = 0.07 ETH
1 JACK = 0.07 ETH
5,000 bids made.
1 JACK = 0.31 ETH
1 JACK = 0.31 ETH
No one cant tell how far it can go.