From fe202607ebb5d2d44ccfb9db208fbd664f3736ca Mon Sep 17 00:00:00 2001
From: Friedel Ziegelmayer <dignifiedquire@gmail.com>
Date: Fri, 20 May 2016 12:50:16 +0200
Subject: [PATCH] first pass at stretchKey

---
 README.md                   |  8 +++-
 src/ephemeral-keys.js       |  7 ++-
 src/key-stretcher.js        | 92 ++++++++++++++++++++++++++++++++++++-
 test/ephemeral-keys.spec.js |  8 +++-
 test/fixtures/go-rsa.key    |  0
 test/key-stretcher.spec.js  | 25 ++++++++++
 6 files changed, 135 insertions(+), 5 deletions(-)
 create mode 100644 test/fixtures/go-rsa.key
 create mode 100644 test/key-stretcher.spec.js

diff --git a/README.md b/README.md
index 49dafd0..78304aa 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,13 @@ Generates an ephemeral public key and returns a function that will compute the s
 
 Focuses only on ECDH now, but can be made more general in the future.
 
-Returns a `Buffer`.
+Returns an object of the form
+```js
+{
+  key: Buffer,
+  genSharedKey: Function
+}
+```
 
 ### `marshalPublicKey(key[, type])`
 
diff --git a/src/ephemeral-keys.js b/src/ephemeral-keys.js
index 12ce31c..ff2f5c2 100644
--- a/src/ephemeral-keys.js
+++ b/src/ephemeral-keys.js
@@ -22,9 +22,14 @@ module.exports = (curveName) => {
 
   const priv = ec.genKeyPair()
 
-  return (theirPub) => {
+  const genSharedKey = (theirPub) => {
     const pub = ec.keyFromPublic(theirPub, 'hex')
 
     return priv.derive(pub.getPublic()).toBuffer('le')
   }
+
+  return {
+    key: priv.getPublic(),
+    genSharedKey
+  }
 }
diff --git a/src/key-stretcher.js b/src/key-stretcher.js
index 0c05312..9751253 100644
--- a/src/key-stretcher.js
+++ b/src/key-stretcher.js
@@ -1,7 +1,97 @@
 'use strict'
 
+const forge = require('node-forge')
+const createBuffer = forge.util.createBuffer
+
+const cipherMap = {
+  'AES-128': {
+    ivSize: 16,
+    keySize: 16
+  },
+  'AES-256': {
+    ivSize: 16,
+    keySize: 32
+  },
+  'Blowfish': {
+    ivSize: 8,
+    cipherKeySize: 32
+  }
+}
+
+const hashMap = {
+  'SHA1': 'sha1',
+  'SHA256': 'sha256',
+  'SHA512': 'sha512'
+}
+
 // 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')
+  const cipher = cipherMap[cipherType]
+  const hash = hashMap[hashType]
+
+  if (!cipher) {
+    throw new Error('unkown cipherType passed')
+  }
+
+  if (!hash) {
+    throw new Error('unkown hashType passed')
+  }
+
+  if (Buffer.isBuffer(secret)) {
+    secret = createBuffer(secret.toString('binary'))
+  }
+
+  const cipherKeySize = cipher.keySize
+	const ivSize = cipher.ivSize
+	const hmacKeySize = 20
+  const seed = 'key expansion'
+  const resultLength = 2 * (ivSize + cipherKeySize + hmacKeySize)
+
+  const m = forge.hmac.create()
+  m.start(hash, secret)
+  m.update(seed)
+
+  let a = m.digest().bytes()
+  const result = createBuffer()
+
+  let j = 0
+  for (; j < resultLength;) {
+    m.start(hash, secret)
+    m.update(a)
+    m.update(seed)
+
+    const b = createBuffer(m.digest(), 'raw')
+    let todo = b.length()
+
+    if (j + todo > resultLength) {
+      todo = resultLength - j
+    }
+
+    result.putBytes(b.getBytes(todo))
+
+    j += todo
+
+    m.start(hash, secret)
+    m.update(a)
+    a = m.digest().bytes()
+  }
+
+  const half = resultLength / 2
+  const r1 = createBuffer(result.getBytes(half))
+  const r2 = createBuffer(result.getBytes())
+
+  const k1 = {
+    IV: r1.getBytes(ivSize),
+    CipherKey: r1.getBytes(cipherKeySize),
+    MacKey: r1.getBytes()
+  }
+
+  const k2 = {
+    IV: r2.getBytes(ivSize),
+    CipherKey: r2.getBytes(cipherKeySize),
+    MacKey: r2.getBytes()
+  }
+
+  return {k1, k2}
 }
diff --git a/test/ephemeral-keys.spec.js b/test/ephemeral-keys.spec.js
index f6a4ea9..30cec4e 100644
--- a/test/ephemeral-keys.spec.js
+++ b/test/ephemeral-keys.spec.js
@@ -7,11 +7,15 @@ const crypto = require('../src')
 
 describe('generateEphemeralKeyPair', () => {
   it('returns a function that generates a shared secret', () => {
-    const maker = crypto.generateEphemeralKeyPair('P-256')
+    const res = crypto.generateEphemeralKeyPair('P-256')
     const ourPublic = '044374add0df35706db7dade25f3959fc051d2ef5166f8a6a0aa632d0ab41cdb4d30e1a064e121ac56155235a6b8d4c5d8fe35e019f507f4e2ff1445e229d7af43'
 
     expect(
-      maker(ourPublic)
+      res.genSharedKey(ourPublic)
     ).to.have.length(32)
+
+    expect(
+      res.key
+    ).to.exist
   })
 })
diff --git a/test/fixtures/go-rsa.key b/test/fixtures/go-rsa.key
new file mode 100644
index 0000000..e69de29
diff --git a/test/key-stretcher.spec.js b/test/key-stretcher.spec.js
new file mode 100644
index 0000000..a8f590e
--- /dev/null
+++ b/test/key-stretcher.spec.js
@@ -0,0 +1,25 @@
+/* eslint-env mocha */
+'use strict'
+
+const expect = require('chai').expect
+
+const crypto = require('../src')
+
+describe('keyStretcher', () => {
+  describe('generate', () => {
+    const ciphers = ['AES-128', 'AES-256', 'Blowfish']
+    const hashes = ['SHA1', 'SHA256'/*, 'SHA512'*/]
+    const res = crypto.generateEphemeralKeyPair('P-256')
+    const secret = res.genSharedKey(res.key)
+
+    ciphers.forEach((cipher) => {
+      hashes.forEach((hash) => {
+        it(`${cipher} - ${hash}`, () => {
+          const keys = crypto.keyStretcher(cipher, hash, secret)
+          expect(keys.k1).to.exist
+          expect(keys.k2).to.exist
+        })
+      })
+    })
+  })
+})