mirror of https://github.com/BTCPrivate/copay.git
124 lines
5.2 KiB
Markdown
124 lines
5.2 KiB
Markdown
[](http://travis-ci.org/bitpay/copay)
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Copay
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=====
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Installation:
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Copy config.template.js to config.js and edit to suit your needs. (Defaults to
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public PeerJS and Insight servers)
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Then execute these commands:
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```
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npm install
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bower install
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grunt --target=dev shell
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node app.js
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```
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To run on a different port:
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```
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PORT=3001 node app.js
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```
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To open up five different instances to test 3-of-5 multisig with yourself, then run this in 5 different terminals:
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```
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PORT=3001 node app.js
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PORT=3002 node app.js
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PORT=3003 node app.js
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PORT=3004 node app.js
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PORT=3005 node app.js
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```
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About Copay
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===========
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General
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-------
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*Copay* implements a multisig wallet using p2sh addresses. It support multiple wallet configurations, like 3-of-5
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(3 required signatures from 5 participant peers) or 2-of-3. To generate addresses to receive coins,
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*Copay* needs the public keys of all the participat peers in the wallet. Those public keys, among the
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wallet configuration, are combined to generate a single address to receive a payment.
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To unlock the payment, and spend the wallet's funds, the needed signatures need to be collected an put togheter
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in the transaction. Each peer manage her own private key, and that key is never transmited to other
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peers. Once a transaction proposal is created, the proposal is distributed among the peers and each peer
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can sign the transaction locally. Once the transaction is complete, the last signing peer will broadcast the
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transaction to the bitcoin network, using a public API for that (Insight API by default in *Copay*)..
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*Copay* also implements BIP32 to generate new addresses for the peers. This mean that the actual piece of
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information shared between the peers is an extended public key, from which is possible to derive more
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public keys so the wallet can use them. Each peer holds for himself his extended private key, to be able
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to sign the incoming transaction proposals.
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Serverless web
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--------------
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*Copay* software does not need an application server to run. All the software is implemented in client-side
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Javascript. For persistent storage, the client browser's *localStorage* is used. This information is
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stored encryped using the peer's password. Also it is possible (and recommended) to backup that information
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with using one of the options provided by *Copay*, like file downloading. Without a proper backup, all
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wallets funds can be lost if the browser's localStorage is deleted, or the browser installation deleted.
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Peer communications
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-------------------
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*Copay* use peer-to-peer (p2p) networking to comunicate the parties. Parties exchange transaction
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proposals, public keys, nicknames and some wallet options. As mentioned above, private keys are *no*
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sent to the network.
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webRTC is the used protocol. A p2p facilitator server is needed to allow the peers to find each other.
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*Copay* uses the open-sourced *peerjs*
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server implementation. Wallet participants can use a public peerjs server or install their own. Once the peers
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find each other, a true p2p connection is established and there is no flow of information to the
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server, only between the peers.
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webRTC uses DTLS to secure communications between the peers, and each peer use a self-signed
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certificate.
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Security model
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--------------
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On top of webRTC, *Copay* peers authenticate as part of the "wallet ring"(WR) by 2 factors: An identity
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key and a network key.
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The *identity key* is a ECDSA public key derived from their extended public
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key using a specific BIP32 branch. This special public key is never used for Bitcoin address creation, and
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should only be know by members of the WR.
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In *Copay* this special public key is named *copayerId*. To register into the peerjs server, while not
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reveling its copayerId to an entity outside the WR, each peer hash the copayerId and pass a SIN
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to the server. peer discovery is then entirely done using peer's SINs. Note that all copayers in the WR
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know the complete copayerIDs of the peers.
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The *network key* is a random key generated when the wallet is created an shared in the initial
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'secret string' that peers distribute while the wallet is been created. The network key is then stored
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by each peer on the wallet configuration. The network key is used for establishing a CCM/AES
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authenticated encrypted channel between all peers, on top of webRTC. The main reason of implementing
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the *network key* is to prevent man-in-the-middle attacks from a compromised peerjs server.
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Secret String
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-------------
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When a wallet is created, a secret string is provided to invite new peers to the new wallet. This string
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has the following format:
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- CopayerId of the peer generating the string. This is a 33 bytes ECDSA public key, as explained above.
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This allow the receiving peer to locate the generating peer.
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- Network Key. A 8 byte string to encrypt and sign the peers communication.
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The string is encoded using bitcoin's Base8Check encoding, to prevent transmision errors.
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Peer authentication
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-------------------
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It is important to note that all data in the wallet is shared between *all peers*, with the exception of each
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peer's private key, with are never transmited throught the network. There is not private messages or, in general,
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information that belongs to a subset of the WR.
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