The WAHKDF class is used to derive keys, salts and nonces for initializing SRTP streams.

WAHKDF.js

const crypto = require("crypto");

// master secret
const keyMaterial = new Buffer(
  "09a38e76fe90e4f126ed66d05a6783bad48776b61daaf7c939c005ea2d8ccdf6",
  "hex"
);
// JID param: 4915905771620@s.whatsapp.net
const info = "3439313539303537373136323040732e77686174736170702e6e6574";
const salt = new Buffer(
  "0000000000000000000000000000000000000000000000000000000000000000",
  "hex"
);
const initialKey = crypto.createHmac("sha256", salt)
                    .update(keyMaterial)
                    .digest();
const temp1 = crypto.createHmac("sha256", initialKey)
                    .update(new Buffer(info + "01", "hex"))
                    .digest();
const temp2 = new Buffer(temp1.toString("hex") + info + "02", "hex");
const temp3 = crypto.createHmac("sha256", initialKey)
                    .update(temp2)
                    .digest();
  
const result = Buffer.concat([temp1, temp3.slice(0, 14)]);
console.log(result.toString("hex"));

// 4633c47f94d5ed5993a6dba8514d5fb85092ba904256f8d34d56e72e665bcd4c5b6c418bdb811e7f84a70c83f401