Copay is an easy-to-use, open-source, multiplatform, multisignature, secure bitcoin wallet platform for both individuals and companies. Copay uses [Bitcore Wallet Service](https://github.com/bitpay/bitcore-wallet-service) (BWS) for peer synchronization and network interfacing.
Binary versions of Copay are available for download at [Copay.io](https://copay.io/#download). Copay Binaries are signed with the key copay@bitpay.com [See here for details](https://github.com/bitpay/copay#how-to-verify-copay-signatures)
- Available for [iOS](https://itunes.apple.com/us/app/copay/id951330296), [Android](https://play.google.com/store/apps/details?id=com.bitpay.copay&hl=en), [Windows Phone](http://www.windowsphone.com/en-us/store/app/copay-wallet/4372479b-a064-4d18-8bd3-74a3bdb81c3a), [Chrome App](https://chrome.google.com/webstore/detail/copay/cnidaodnidkbaplmghlelgikaiejfhja?hl=en), [Linux](https://github.com/bitpay/copay/releases/latest), [Windows](https://github.com/bitpay/copay/releases/latest) and [OS X](https://github.com/bitpay/copay/releases/latest) devices
> **Note:** Other browser extensions could have access to Copay internal data and compromise the user's private key when running Copay as a web page. For optimal security, you should disable all third-party browser extensions when using Copay in this manner.
On success, the Chrome extension will be located at: `browser-extensions/chrome/copay-chrome-extension`. To install it go to `chrome://extensions/` in your browser and ensure you have the 'developer mode' option enabled in the settings. Then click on "Load unpacked chrome extension" and choose the directory mentioned above.
Copay implements a multisig wallet using [p2sh](https://en.bitcoin.it/wiki/Pay_to_script_hash) addresses. It supports multiple wallets, each with with its own configuration, such as 3-of-5 (3 required signatures from 5 participant peers) or 2-of-3. To create a multisig wallet shared between multiple participants, Copay requires the extended public keys of all the wallet participants. Those public keys are then incorporated into the wallet configuration and combined to generate a payment address where funds can be sent into the wallet. Conversely, each participant manages their own private key and that private key is never transmitted anywhere.
To unlock a payment and spend the wallet's funds, a quorum of participant signatures must be collected and assembled in the transaction. The funds cannot be spent without at least the minimum number of signatures required by the wallet configuration (2 of 3, 3 of 5, 6 of 6, etc). Once a transaction proposal is created, the proposal is distributed among the wallet participants for each to sign the transaction locally. Finally, when the transaction is signed, the last signing participant will broadcast the transaction to the Bitcoin network.
Copay also implements [BIP32](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki) to generate new addresses for peers. The public key that each participant contributes to the wallet is a BIP32 extended public key. As additional public keys are needed for wallet operations (to produce new addresses to receive payments into the wallet, for example) new public keys can be derived from the participants' original extended public keys. Once again, it's important to stress that each participant keeps their own private keys locally - private keys are not shared - and are used to sign transaction proposals to make payments from the shared wallet.
For more information regarding how addresses are generated using this procedure, see: [Structure for Deterministic P2SH Multisignature Wallets](https://github.com/bitcoin/bips/blob/master/bip-0045.mediawiki).
Copay encrypts the backup with the [Stanford JS Crypto Library](http://bitwiseshiftleft.github.io/sjcl/). To extract the private key of your wallet you can use https://bitwiseshiftleft.github.io/sjcl/demo/, copy the backup to 'ciphertext' and enter your password. The resulting JSON will have a key named: `xPrivKey`, that is the extended private key of your wallet. That information is enough to sign any transaction from your wallet, so be careful when handling it!
The backup also contains the key `publicKeyRing` that holds the extended public keys of the Copayers. Using a tool like [Bitcore PlayGround](http://bitcore.io/playground/#/multisig), and following [BIP45](https://github.com/bitcoin/bips/blob/master/bip-0045.mediawiki) it is possible to generate all wallet address. Note that addresses generated at BWS use the 'shared cosigner index' (2147483647) so Copay address indexes look like: `m/45'/2147483647/0/x` for main addresses and `m/45'/2147483647/1/y` for change addresses, where `x` and `y` are integers starting from `0`. The maximum values of `x` and `y` depend on the wallet usage, and in a restore procedure, the generated addresses are scanned on the blockchain for transactions (this is the 'scan' procedure that you can see inside the Copay App settings). To generate the wallet addresses, the required number of Copayers also need to be specified (backup key `m`).
Copay depends on [Bitcore Wallet Service](https://github.com/bitpay/bitcore-wallet-service) (BWS) for blockchain information, networking and Copayer synchronization. A BWS instance can be setup and operational within minutes or you can use a public instance like `https://bws.bitpay.com`. Switching between BWS instances is very simple and can be done with a click from within Copay. BWS also allows Copay to interoperate with others wallet like [Bitcore Wallet CLI] (https://github.com/bitpay/bitcore-wallet).
Copay uses standard gettext PO files for translations and [Crowdin](https://crowdin.com/project/copay) as the front-end tool for translators. To join our team of translators, please create an account at [Crowdin](https://crowdin.com) and translate the Copay documentation and application text into your native language.
Copay uses the `MAJOR.MINOR.BATCH` convention for versioning. Any release that adds features should modify the MINOR or MAJOR number.
### Bug Fixing Releases
We release bug fixes as soon as possible for all platforms. Usually around a week after patches, a new release is made with language translation updates (like 1.1.4 and then 1.1.5). There is no coordination so all platforms are updated at the same time.
- t+0: tag the release 1.2 and "text lock" (meaning only non-text related bug fixes. Though this rule is sometimes broken, it's good to make a rule.)
- t+7: testing for 1.2 is finished, translation is also finished, and 1.2.1 is tagged with all translations along with bug fixes made in the last week.
- t+7: iOS is submitted for 1.2.1. All other platforms are submitted with auto-release off.
- t + (~17): All platforms 1.2.1 are released when Apple approves the iOS application update.
Copay is released under the MIT License. Please refer to the [LICENSE](https://github.com/bitpay/copay/blob/master/LICENSE) file that accompanies this project for more information including complete terms and conditions.
