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Ethereum based time-locked wallet contracts and DApp to keep ether and ERC20 tokens
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Time Locked Wallet - TopCoder/ConsenSys Hackathon

Update: this project won a prize in ConsenSys/Topcoder - uPort Blockchain and Identity Hackathon:

Time Locked Wallets - Use Cases

There are many different applications of the Ethereum smart contracts, the most popular at the moment being cryptocurrencies aka ERC20 tokens and crowd funding token sales aka ICOs. In this hackathon, I would like to explore something different, like the idea of locking funds in crypto wallet contracts.

Here are several examples, starting with, probably the most common reason at the moment, to lock the funds called vesting. Imagine that you have just raised a successful ICO and your company still holds a majority of the tokens distributed between the team members. It would be beneficial to all the parties to ensure that the tokens hold by employees cannot be traded straight away. If they are no controls in place, employees might take action and sell all of them, cash out and quit the company. At the same time it would negatively affect the market price and make all the contributors to the project unhappy.

Another idea is to use smart contract as a crypto will/testament. Imagine I would like to store my crypto savings in a contract which will be accessible by members of the family, but only after something has happened to me. Let's say I should 'check-in' with the wallet, by evoking some contract call every so-often. If I don't check in on time, something might have happened to me and they can withdraw the funds. Either by reaching a consensus between the family members or by explicitly setting in the contract the proportions of the funds corresponding to each of them.

Different application of locking funds could be to create a small pension fund or time based safe/saving account that prevents the owner from withdrawing the funds before a certain time in the future. It could be particurarly useful for addicted crypto traders in helping keep their Ether intact e.g. HODL wallet. Also, what is a use case for this hackathon, to put some crypto money away for later for someone else, like a future birthday gift.


Why don't I introduce the actors of the demo first. Lets assume Alice is going to be the creator of the time locked wallet and Bob will be the recipient/owner of the funds.

Here comes the demo outline:

  • Alice creates a time locked wallet for Bob and sends some ETH
  • Alice additionally sends some ERC20 TopCoder tokens
  • Bob can see the wallets he has access to and the ones he created
  • Bob cannot withdraw any funds before the wallet time lock expires or is empty
  • Bob withdraws the ETH when the wallet gets unlocked
  • Bob withdraws all TopCoder tokens

The demo is recorded and uploaded here:

Technical Details

There are three contracts of essence to this demo: TimeLockedWallet.sol, TimeLockedWalletFactory.sol and TopCoderToken.sol.

TimeLockedWalletFactory is deployed to Rinkeby test network here: and TopCoderToken here: A new TimeLockedWallet contract is deployed automatically by calling newTimeLockedWallet on the TimeLockedWalletFactory.

Running Locally

Firstly, install Node and Git on your machine. Once it's done install Truffle with:

npm install -g truffle

Checkout this project source code:

git clone
cd uport-time-locked-wallets

And then compile and migrate the contracts:

truffle develop
> compile
> migrate

Finally, you can run the DApp:

npm run dev

which will launch a browser tab on http://localhost:3000/.

Install the uPort app on your smartphone and give it a go.


I've discovered the following issues:

  • When sending Ether using payable methods on uPort wrapped contract object, invalid value is sent. I filed a bug report here:
  • Rinkeby Etherscan is not reflecting correctly TimeLockedWallet contracts, probably because they were deployed from within the factory contract. Neither it is showing correctly all Ether transactions.
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