Add node modules and compiled JavaScript from main (#54)

Co-authored-by: Oliver King <oking3@uncc.edu>

node_modules/jose/lib/jwa/ecdh/derive.js

@@ -0,0 +1,40 @@
+const { createHash } = require('crypto')
+const ecdhComputeSecret = require('./compute_secret')
+
+const concat = (key, length, value) => {
+  const iterations = Math.ceil(length / 32)
+  let res
+
+  for (let iter = 1; iter <= iterations; iter++) {
+    const buf = Buffer.allocUnsafe(4 + key.length + value.length)
+    buf.writeUInt32BE(iter, 0)
+    key.copy(buf, 4)
+    value.copy(buf, 4 + key.length)
+    if (!res) {
+      res = createHash('sha256').update(buf).digest()
+    } else {
+      res = Buffer.concat([res, createHash('sha256').update(buf).digest()])
+    }
+  }
+
+  return res.slice(0, length)
+}
+
+const uint32be = (value, buf = Buffer.allocUnsafe(4)) => {
+  buf.writeUInt32BE(value)
+  return buf
+}
+
+const lengthAndInput = input => Buffer.concat([uint32be(input.length), input])
+
+module.exports = (alg, keyLen, privKey, pubKey, { apu = Buffer.alloc(0), apv = Buffer.alloc(0) } = {}, computeSecret = ecdhComputeSecret) => {
+  const value = Buffer.concat([
+    lengthAndInput(Buffer.from(alg)),
+    lengthAndInput(apu),
+    lengthAndInput(apv),
+    uint32be(keyLen)
+  ])
+
+  const sharedSecret = computeSecret(privKey, pubKey)
+  return concat(sharedSecret, keyLen / 8, value)
+}