feat: implement generateEphemeralKeyPair

README.md

@@ -18,7 +18,6 @@ needed for libp2p. This is based on this [go implementation](https://github.com/
 
 ## API
 
-
 ### `generateKeyPair(type, bits, cb)`
 
 - `type: String`, only `'RSA'` is currently supported
@@ -27,6 +26,16 @@ needed for libp2p. This is based on this [go implementation](https://github.com/
 
 Generates a keypair of the given type and bitsize.
 
+### `generateEphemeralKeyPair(curve)`
+
+- `curve: String`, one of `'P-256'`, `'P-384'`, `'P-521'` is currently supported
+
+Generates an ephemeral public key and returns a function that will compute the shared secret key.
+
+Focuses only on ECDH now, but can be made more general in the future.
+
+Returns a `Buffer`.
+
 ### `marshalPublicKey(key[, type])`
 
 - `key: crypto.rsa.RsaPublicKey`

package.json

@@ -25,6 +25,7 @@
   "author": "Friedel Ziegelmayer <dignifiedqurie@gmail.com>",
   "license": "MIT",
   "dependencies": {
+    "elliptic": "^6.2.3",
     "multihashing": "^0.2.1",
     "node-forge": "^0.6.39",
     "protocol-buffers": "^3.1.6"

src/ephemeral-keys.js

@@ -0,0 +1,30 @@
+'use strict'
+
+const EC = require('elliptic').ec
+
+const curveMap = {
+  'P-256': 'p256',
+  'P-384': 'p384',
+  'P-521': 'p521'
+}
+
+// Generates an ephemeral public key and returns a function that will compute
+// the shared secret key.
+//
+// Focuses only on ECDH now, but can be made more general in the future.
+module.exports = (curveName) => {
+  const curve = curveMap[curveName]
+  if (!curve) {
+    throw new Error('unsupported curve passed')
+  }
+
+  const ec = new EC(curve)
+
+  const priv = ec.genKeyPair()
+
+  return (theirPub) => {
+    const pub = ec.keyFromPublic(theirPub, 'hex')
+
+    return priv.derive(pub.getPublic()).toBuffer('le')
+  }
+}

src/index.js

@@ -8,6 +8,9 @@ const pbm = protobuf(fs.readFileSync(path.join(__dirname, './crypto.proto')))
 exports.utils = require('./utils')
 const keys = exports.keys = require('./keys')
 
+exports.keyStretcher = require('./key-stretcher')
+exports.generateEphemeralKeyPair = require('./ephemeral-keys')
+
 // Generates a keypair of the given type and bitsize
 exports.generateKeyPair = (type, bits, cb) => {
   let key = keys[type.toLowerCase()]
@@ -18,20 +21,6 @@ exports.generateKeyPair = (type, bits, cb) => {
   key.generateKeyPair(bits, cb)
 }
 
-// Generates an ephemeral public key and returns a function that will compute
-// the shared secret key.
-//
-// Focuses only on ECDH now, but can be made more general in the future.
-exports.generateEphemeralKeyPair = (curveName, cb) => {
-  throw new Error('Not implemented')
-}
-
-// Generates a set of keys for each party by stretching the shared key.
-// (myIV, theirIV, myCipherKey, theirCipherKey, myMACKey, theirMACKey)
-exports.keyStretcher = (cipherType, hashType, secret) => {
-  throw new Error('Not implemented')
-}
-
 // Converts a protobuf serialized public key into its
 // representative object
 exports.unmarshalPublicKey = (buf) => {

src/key-stretcher.js

@@ -0,0 +1,7 @@
+'use strict'
+
+// Generates a set of keys for each party by stretching the shared key.
+// (myIV, theirIV, myCipherKey, theirCipherKey, myMACKey, theirMACKey)
+module.exports = (cipherType, hashType, secret) => {
+  throw new Error('Not implemented')
+}

test/ephemeral-keys.spec.js

@@ -0,0 +1,17 @@
+/* eslint-env mocha */
+'use strict'
+
+const expect = require('chai').expect
+
+const crypto = require('../src')
+
+describe('generateEphemeralKeyPair', () => {
+  it('returns a function that generates a shared secret', () => {
+    const maker = crypto.generateEphemeralKeyPair('P-256')
+    const ourPublic = '044374add0df35706db7dade25f3959fc051d2ef5166f8a6a0aa632d0ab41cdb4d30e1a064e121ac56155235a6b8d4c5d8fe35e019f507f4e2ff1445e229d7af43'
+
+    expect(
+      maker(ourPublic)
+    ).to.have.length(32)
+  })
+})