Open Savings Initiative lets you set aside cryptocurrency that can only be spent after a certain date. It's like a certificate of deposit that you can add more money to anytime, but doesn't require a bank.
You can also use it to gift money that can't be spent until a certain date, like writing a cheque for a future date, except it can't bounce or be cancelled.
The app accomplishes this by utilizing features of the blockchain protocol, rather than depending on some custom infrastructure.
The Open Savings Initiative app is built with Typescript, Anuglar, and Electron, and can be packaged for deployment to the web, or as a native Windows/Mac/Linux desktop app.
This app was developed by Ransom Christofferson and the Prestige IT team with guidance from Yeoman's Capital, and was funded by a generous donation from Ricardo Jimenez.
Development was bootstrapped from maximegris/angular-electron.
The Open Savings Initiative logo was built from two icons created by AllienWorks, licenced under CC BY 3.0.
TL;DR---The app uses the OP_CHECKLOCKTIMEVERIFY opcode to build a pay-to-script-hash (P2SH) address. The coins sent to the P2SH address are only spendable by a newly generated private key, which is given to the user for safe keeping, digitally or printed. This effectively creates a time-locked paper wallet.
The script used to build the P2SH (i.e. the "redeem script") is:
<timestamp> OP_CHECKLOCKTIMEVERIFY OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG
This is a standard pay-to-pubkey-hash (P2PKH) script, but with a time-locking element added to it. The script to spend coins at this P2SH address (i.e. the "scriptSig") is:
<sig> <pubKey> <redeemScript>
Just as with a common P2PKH transaction, only the owner of a specific address may spend the coins sent to the P2SH address. We'll call this person the "recipient".
<timestamp> is a date and time specified by the user---the coins are unspendable until this time.
<pubKeyHash> is the recipient's address.
<sig> is the signature of the transaction, signed with the recipient's private key.
<pubKey> is the recipient's public key.
<redeemScript> is the serialized redeem script.
The recipient's private key must be used in order to spend the time-locked coins, and typical wallets don't support spending from nonstandard P2SH address like this one. To get around this problem (and not require the user to export his wallet's private keys in order to use them in this app), the app generates a fresh private key to use as the recipient. The user must keep this private key safe.
The user is given this new private key, along with the redeem script. This is all that's needed to spend the coins.
Use Node 12 with this repo.
Clone this repository locally and install dependencies with npm:
git clone https://github.com/coinbackup/opensavings.git
cd opensavings
npm install| Command | Description |
|---|---|
npm start |
Run the app in electron |
npm run ng:serve:web |
Run the app in the browser with hot reload (native libraries don't work in this mode) |
npm run build:prod:web |
Build the app with Angular aot, packaged for deployment as a website. The files will be in dist. |
npm run electron:linux |
Builds the app as a native linux application |
npm run electron:windows |
On Windows, builds the app as a native Windows application |
npm run electron:mac |
On Mac OS, builds the app as a native Mac application |
See maximegris/angular-electron for more dev/build commands.
The app uses bitcore-lib and bitcore-lib-cash to handle most operations. The custom P2SH address and scriptSig are built in TimeLockService (services/time-lock/time-lock.service.ts).
Transactions are built in components/redeem/redeem.component.ts.
The app makes HTTP calls to certain bitcoin nodes which expose a public REST API to read data from the blockchain or broadcast transactions to it.
BlockchainService -> BlockchainType -> Explorer -> NetworkService
- To read from or broadcast to the blockchain, call methods on the
BlockchainService (services/blockchain/blockchain.service.ts). This service makes http requests to multiple APIs simultaneously, to achieve high availability. - APIs and endpoint URLs for BTC, BCH, and their testnets are defined in
BlockchainType (models/blockchain-types.ts). - API responses are handled and normalized in
Explorerclasses(models/explorer-types.ts). - Raw http requests are handled in
NetworkService (services/network/network.service.ts).
To add another API endpoint, define its behavior in models/explorer-types.ts, and add its URL in models/blockchain-types.ts.