From 002969f78d46a0788fe02cd815dc713974f5c7e3 Mon Sep 17 00:00:00 2001
From: Emil Bay <github@tixz.dk>
Date: Thu, 15 Feb 2018 22:31:13 +0100
Subject: [PATCH] Preliminary kx api

Missing dependent apis and tests
---
 crypto_kx.js | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 crypto_kx.js

diff --git a/crypto_kx.js b/crypto_kx.js
new file mode 100644
index 0000000..f7d60c9
--- /dev/null
+++ b/crypto_kx.js
@@ -0,0 +1,79 @@
+var assert = require('nanoassert')
+var randombytes_buf = require('./randombytes').randombytes_buf
+var generichash = require('./crypto_generichash')
+var crypto_scalarmult_base = require('./crypto_scalarmult').crypto_scalarmult_base
+
+exports.crypto_kx_PUBLICKEYBYTES = 32
+exports.crypto_kx_SECRETKEYBYTES = 32
+exports.crypto_kx_SEEDBYTES = 32
+exports.crypto_kx_SESSIONKEYBYTES = 32
+exports.crypto_kx_PRIMITIVE = ''
+
+exports.crypto_kx_keypair = function (pk, sk) {
+  assert(sk.byteLength >= exports.crypto_kx_SECRETKEYBYTES, 'sk must be at least crypto_kx_SECRETKEYBYTES')
+  assert(pk.byteLength >= exports.crypto_kx_PUBLICKEYBYTES, 'pk must be at least crypto_kx_PUBLICKEYBYTES')
+
+  randombytes_buf(sk.subarray(0, exports.crypto_kx_SECRETKEYBYTES))
+
+  crypto_scalarmult_base(
+    pk.subarray(0, exports.crypto_kx_PUBLICKEYBYTES),
+    sk.subarray(0, exports.crypto_kx_SECRETKEYBYTES)
+  )
+}
+
+exports.crypto_kx_seed_keypair = function (pk, sk, seed) {
+  assert(sk.byteLength >= exports.crypto_kx_SECRETKEYBYTES, 'sk must be at least crypto_kx_SECRETKEYBYTES')
+  assert(pk.byteLength >= exports.crypto_kx_PUBLICKEYBYTES, 'pk must be at least crypto_kx_PUBLICKEYBYTES')
+  assert(seed.byteLength >= exports.crypto_kx_SEEDBYTES, 'seed must be at least crypto_kx_SEEDBYTES')
+
+  generichash.crypto_generichash(
+    sk.subarray(0, exports.crypto_kx_SECRETKEYBYTES),
+    seed.subarray(0, exports.crypto_kx_SEEDBYTES)
+  )
+
+  crypto_scalarmult_base(
+    pk.subarray(0, exports.crypto_kx_PUBLICKEYBYTES),
+    sk.subarray(0, exports.crypto_kx_SECRETKEYBYTES)
+  )
+}
+
+exports.crypto_kx_client_session_keys = calc.bind(null, false)
+
+exports.crypto_kx_server_session_keys = calc.bind(null, true)
+
+
+function calc (server, rx, tx, pk, sk, remote_pk) {
+  if (rx == null) rx = tx
+  if (tx == null) tx = rx
+
+  assert(rx >= exports.crypto_kx_SESSIONKEYBYTES, 'rx must be at least crypto_kx_SESSIONKEYBYTES')
+  assert(tx >= exports.crypto_kx_SESSIONKEYBYTES, 'tx should be at least crypto_kx_SESSIONKEYBYTES')
+  assert(sk.byteLength >= exports.crypto_kx_SECRETKEYBYTES, 'sk must be at least crypto_kx_SECRETKEYBYTES')
+  assert(pk.byteLength >= exports.crypto_kx_PUBLICKEYBYTES, 'pk must be at least crypto_kx_PUBLICKEYBYTES')
+  assert(remote_pk.byteLength >= exports.crypto_kx_PUBLICKEYBYTES, 'remote_pk must be at least crypto_kx_PUBLICKEYBYTES')
+
+  rx = rx.subarray(0, exports.crypto_kx_SESSIONKEYBYTES)
+  tx = tx.subarray(0, exports.crypto_kx_SESSIONKEYBYTES)
+
+  sk = sk.subarray(0, exports.crypto_kx_SECRETKEYBYTES)
+  pk = pk.subarray(0, exports.crypto_kx_PUBLICKEYBYTES)
+  remote_pk = remote_pk.subarray(0, exports.crypto_kx_PUBLICKEYBYTES)
+
+  var keys = new Uint8Array(2 * exports.crypto_kx_SESSIONKEYBYTES)
+  var hash = generichash.crypto_generichash_instance(null, keys.byteLength)
+  var q = new Uint8Array(scalarmult.crypto_scalarmult_BYTES)
+
+  scalarmult.crypto_scalamult(q, sk, remote_pk)
+
+  hash.update(q)
+  q.fill(0)
+  // if server, then remote_pk == client_pk
+  hash.update(server ? remote_pk : pk)
+  hash.update(server ? pk : remote_pk)
+  hash.final(keys)
+
+  // TODO clear out hash
+
+  rx.set(keys.subarray(0, exports.crypto_kx_SESSIONKEYBYTES))
+  tx.set(keys.subarray(exports.crypto_kx_SESSIONKEYBYTES))
+}