<commit_before>[![Build Status](https://secure.travis-ci.org/bitpay/copay.png)](http://travis-ci.org/bitpay/copay)

Copay
=====

Installation:

Copy config.template.js to config.js and edit to suit your needs. (Defaults to
public PeerJS and Insight servers)

Then execute these commands:
```
npm install
bower install
grunt --target=dev shell
node app.js
```

To run on a different port:
```
PORT=3001 node app.js
```

To open up five different instances to test 3-of-5 multisig with yourself, then run this in 5 different terminals:
```
PORT=3001 node app.js
PORT=3002 node app.js
PORT=3003 node app.js
PORT=3004 node app.js
PORT=3005 node app.js
```

About Copay
===========

General
-------

*Copay* implements a multisig wallet using p2sh addresses. It supports multiple wallet configurations, like
3-of-5 (3 required signatures from 5 participant peers) or 2-of-3. To generate addresses to receive coins,
*Copay* needs the public keys of all the participant peers in the wallet. Those public keys, among the 
wallet configuration, are combined to generate a single address to receive a payment.  

To unlock the payment, and spend the wallet's funds, the needed signatures need to be collected and put
togheter in the transaction. Each peer manages her own private key, and that key is never transmited to
other peers. Once a transaction proposal is created, the proposal is distributed among the peers and each peer
can sign the transaction locally. Once the signing is complete, the last signing peer will broadcast the 
transaction to the bitcoin network, using a public API for that (Insight API by default in *Copay*)..

*Copay* also implements BIP32 to generate new addresses for the peers. This means that the actual piece of 
information shared between the peers is an extended public key, from which it is possible to derive more
public keys so the wallet can use them. Each peer holds for himself his extended private key, to be able
to sign the incoming transaction proposals.

Serverless web
--------------
*Copay* software does not need an application server to run. All the software is implemented in client-side
Javascript. For persistent storage, the client browser's *localStorage* is used. This information is
stored encryped using the peer's password. Also it is possible (and recommended) to backup that information
with using one of the options provided by *Copay*, like file downloading. Without a proper backup, all 
wallets funds can be lost if the browser's localStorage is deleted, or the browser installation deleted.

Peer communications
-------------------
*Copay* use peer-to-peer (p2p) networking for comunication between the parties. Parties exchange transaction 
proposals, public keys, nicknames and some wallet options. As mentioned above, private keys are *not*
sent to the network. 

webRTC is the used protocol for p2p communication. A p2p facilitator server is needed to allow the peers
to find each other. *Copay* uses the open-sourced *peerjs* server implementation. Wallet participants
can use a public peerjs server or install their own. Once the peers find each other, a true p2p
connection is established and there is no flow of information to the server, only between the peers.

webRTC uses DTLS to secure communications between the peers, and each peer uses a self-signed
certificate.

Security model
--------------
On top of webRTC, *Copay* peers authenticate as part of the "wallet ring"(WR) by 2 factors: An identity 
key and a network key. 

The *identity key* is a ECDSA public key derived from peers' extended public key using a specific BIP32
branch. This special public key is never used for Bitcoin address creation, and should only be know by
members of the WR. 
In *Copay* this special public key is named *copayerId*. To register into the peerjs server, while not
reveling its copayerId to an entity outside the WR, each peer hashes the copayerId and sends a SIN 
to the server. peer discovery is then entirely done using the peer's SINs. Note that all copayers in
the WR know the complete copayerIDs of the peers.

The *network key* is a random key generated when the wallet is created an shared in the initial 
'secret string' that peers distribute while the wallet is been created. The network key is then stored 
by each peer in their wallet configuration. The network key is used for establishing a CCM/AES 
authenticated encrypted channel between all peers, on top of webRTC. The main reason for implementing
the *network key* is to prevent man-in-the-middle attacks from a compromised peerjs server.

Secret String
-------------
When a wallet is created, a secret string is provided to invite new peers to the new wallet. This string
has the following format:

  - CopayerId of the peer generating the string. This is a 33 byte ECDSA public key, as explained above.
This allow the receiving peer to locate the generating peer.
  - Network Key. A 8 byte string to encrypt and sign the peers communication.

The string is encoded using bitcoin's Base8Check encoding, to prevent transmision errors.

Peer authentication
-------------------

It is important to note that all data in the wallet is shared between *all peers*, with the exception of each
peer's private key, which are never transmited throught the network. There are no private messages or, in general,
information that belongs to a subset of the WR. 










<commit_msg>Copyedit readme This started out as spelling and grammar fixes, but a bit of structural editing crept in.  Please review and send feedback.<commit_after>[![Build Status](https://secure.travis-ci.org/bitpay/copay.png)](http://travis-ci.org/bitpay/copay)

Copay
=====

Installation:

Copy config.template.js to config.js 

and edit to suit your needs. (Defaults to public PeerJS and Insight servers)

Copy bitcore/browser/bundle.js to copay/lib/bitcore.js

Then execute these commands:
```
npm install
bower install
grunt --target=dev shell
node app.js
```

To run on a different port:
```
PORT=3001 node app.js
```

To open up five different instances to test 3-of-5 multisig with yourself, then run this in 5 different terminals:
```
PORT=3001 node app.js
PORT=3002 node app.js
PORT=3003 node app.js
PORT=3004 node app.js
PORT=3005 node app.js
```

About Copay
===========

General
-------

*Copay* implements a multisig wallet using p2sh addresses. It supports multiple wallet configurations, 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* needs the public keys of all the wallet participants. Those public keys are incorporated into the 
wallet configuration and are combined to generate a payment address with which funds can be sent into the wallet.  

To unlock the 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). 
Each participant manages their own private key, and that private key is never transmitted anywhere. 
Once a transaction proposal is created, the proposal is distributed among the 
wallet participants for each participant to sign the transaction locally. 
Once the transaction is signed, the last signing participant will broadcast the 
transaction to the Bitcoin network using a public API (defaults to the Insight API).

*Copay* also implements BIP32 to generate new addresses for the peers. The public key 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. Each participant keeps their own private keys locally. Private keys are not shared. 
Private keys are used to sign transaction proposals to make a payment from the shared wallet.

Serverless web
--------------
*Copay* software does not need an application server to run. All the software is implemented in client-side
JavaScript. For persistent storage, the client browser's *localStorage* is used. Locally stored data is
encrypted using a password provided by the local user. Data kept in browser local storage should be
backed up for safekeeping using one of the methods provided by *Copay*, such as downloading the data into a file.  
Without a proper backup of the user's private key data, all funds stored in the 
wallet may be lost or inaccessible if the browser's localStorage is deleted, the browser uninstalled, 
the local hard disk fails, etc.

Peer communications
-------------------
*Copay* uses peer-to-peer (p2p) networking to communicate between wallet participants. Participants exchange transaction 
proposals, public keys, nicknames and information about the wallet configuration. Private keys are *not* shared with anyone. 

*Copay* network communications use the webRTC protocol. A p2p facilitator server is needed to enable the peers to find each other.
 *Copay* uses the open-sourced *peerjs* server implementation for p2p discovery. Wallet participants can use a 
 public peerjs server or install their own. Once the peers find each other, a true p2p connection is established between the
 peers and there is no further flow of information to the p2p discovery server.

webRTC uses DTLS to secure communications between the peers, and each peer uses a self-signed
certificate.

Security model
--------------
On top of webRTC, *Copay* peers authenticate as part of the "wallet ring"(WR) using an identity 
key and a network key. 

The *identity key* is a ECDSA public key derived from the participant's extended public 
key using a specific BIP32 branch. This special public key is never used for Bitcoin address creation, and
should only be known by members of the WR. 
In *Copay* this special public key is named *copayerId*.  The copayerId is hashed and the hash is used to 
register with the peerjs server. Registering with a hash avoids disclosing the copayerId to parties outside of the WR.
Peer discovery is accomplished using only the hashes of the WR members' copayerIds. All members of the WR
know the full copayerIds of all the other members of the WR.

The *network key* is a random key generated and distributed among the wallet members during wallet creation. 
The network key is stored by each peer in the wallet configuration. The network key is used in establishing a CCM/AES 
authenticated encrypted channel between all members of the WR, on top of webRTC. Use of this
*network key* prevents man-in-the-middle attacks from a compromised peerjs server.

Secret String
-------------
When a wallet is created, a secret string is provided to invite new peers to the new wallet. This string
has the following format:

  - CopayerId of the peer generating the string. This is a 33 byte ECDSA public key, as explained above.
This allows the receiving peer to locate the generating peer.
  - Network Key. A 8 byte string to encrypt and sign the peers communication.

The string is encoded using Bitcoin's Base58Check encoding, to prevent transmission errors.

Peer Authentication
-------------------

It is important to note that - except for private keys - *all data* in the wallet is shared with *all members of the wallet*. 
Private keys are never shared with anyone and are never sent over the network. There are no *private* messages between 
individual members of the wallet. All members of a wallet see everything that happens in that wallet.











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