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https://github.com/dchest/ed2curve-js

Convert Ed25519 signing keys into Curve25519 Diffie-Hellman keys
https://github.com/dchest/ed2curve-js

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Convert Ed25519 signing keys into Curve25519 Diffie-Hellman keys

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README 

        
ed2curve.js

===========



Convert Ed25519 signing key pair into Curve25519 key pair suitable for

Diffie-Hellman key exchange. This means that by exchanging only 32-byte

Ed25519 public keys users can both sign and encrypt with NaCl.



Note that there's currently [no proof](http://crypto.stackexchange.com/a/3311/291)

that this is safe to do. It is safer to share both Ed25519 and Curve25519

public keys (their concatenation is 64 bytes long).



Written by Dmitry Chestnykh in 2014-2016, using public domain code from

[TweetNaCl.js](https://github.com/dchest/tweetnacl-js). Public domain.

No warranty.



Thanks to [@CodesInChaos](https://github.com/CodesInChaos) and

[@nightcracker](https://github.com/nightcracker) for showing how to

convert Edwards coordinates to Montgomery coordinates.



[![Build Status](https://travis-ci.org/dchest/ed2curve-js.svg?branch=master)

](https://travis-ci.org/dchest/ed2curve-js)



Installation

------------



Via NPM:



    $ npm install ed2curve



or just download `ed2curve.js` or `ed2curve.min.js` and include it after

[TweetNaCl.js](https://github.com/dchest/tweetnacl-js):



```html



```



Usage

-----



### ed2curve.convertKeyPair(keyPair) -> convertedKeyPair | null



Converts the given key pair as generated by

[TweetNaCl.js](https://github.com/dchest/tweetnacl-js)'s `nacl.sign.keyPair`

into a key pair suitable for operations which accept key pairs generated by

`nacl.box.keyPair`. This function is a combination of `convertPublicKey`

and `convertSecretKey`.



Returns `null` if the public key in the given key pair is not a valid

Ed25519 public key.



### ed2curve.convertPublicKey(edPublicKey) -> curvePublicKey | null



Converts a 32-byte Ed25519 public key into a 32-byte Curve25519 public key

and returns it.



Returns `null` if the given public key in not a valid Ed25519 public key.



### ed2curve.convertSecretKey(edSecretKey) -> curveSecretKey



Converts a 64-byte Ed25519 secret key (or just the first 32-byte part of it,

which is the secret value) into a 32-byte Curve25519 secret key and returns it.



Example

-------



(Note: example uses [tweetnacl-util](https://github.com/dchest/tweetnacl-util-js)

to convert bytes)



```javascript

// Generate new sign key pair.

var myKeyPair = nacl.sign.keyPair();



// Share public key with a peer.

console.log(myKeyPair.publicKey);



// Receive peer's public key.

var theirPublicKey = // ... receive



// Sign a message.

var message = nacl.util.decodeUTF8('Hello!');

var signedMessage = nacl.sign(message, myKeyPair.secretKey);



// Send message to peer. They can now verify it using

// the previously shared public key (myKeyPair.publicKey).

// ...



// Receive a signed message from peer and verify it using their public key.

var theirSignedMessage = // ... receive

var theirMessage = nacl.sign.open(theirSignedMessage, theirPublicKey);

if (theirMessage) {

  // ... we got the message ...

}



// Encrypt a message to their public key.

// But first, we need to convert our secret key and their public key

// from Ed25519 into the format accepted by Curve25519.

//

// Note that peers are not involved in this conversion -- all they need

// to know is the signing public key that we already shared with them.



var theirDHPublicKey = ed2curve.convertPublicKey(theirPublicKey);

var myDHSecretKey = ed2curve.convertSecretKey(myKeyPair.secretKey);



var anotherMessage = nacl.util.decodeUTF8('Keep silence');

var encryptedMessage = nacl.box(anotherMessage, nonce, theirDHPublicKey, myDHSecretKey);



// When we receive encrypted messages from peers,

// we need to use converted keys to open them.



var theirEncryptedMessage = // ... receive

var decryptedMessage = nacl.box.open(theirEncryptedMessage, nonce, theirDHPublicKey, myDHSecretKey);

```



Requirements

------------



* Requires [TweetNaCl.js](https://github.com/dchest/tweetnacl-js)

* Works in the same enviroments as it.



Other libraries

---------------



Some other libraries that can use a single Ed/Curve25519 key:



* [agl/../extra25519](https://github.com/agl/ed25519/blob/master/extra25519/extra25519.go) - Go

  (compatible with ed2curve)

* [CodesInChaos/../MontgomeryCurve25519](https://github.com/CodesInChaos/Chaos.NaCl/blob/master/Chaos.NaCl/MontgomeryCurve25519.cs) - C#

  (compatible with ed2curve)

* [nightcracker/ed25519](https://github.com/nightcracker/ed25519/blob/master/src/key_exchange.c) - C

  (compatible with ed2curve)

* [libsodium](https://github.com/jedisct1/libsodium) - C

  (compatible with ed2curve)

* [trevp/../curve_sigs](https://github.com/trevp/ref10_extract/blob/master/ed25519/additions/curve_sigs.c) - C

  (incompatible, as it converts the opposite way, and stores a sign bit of signing public key in a signature)