Federal authorities have not been able to execute wiretapping warrants on WhatsApp users. WhatsApp has been upgrading encryption for its messages and VOIP calls. WhatsApp is not involved in any of the criminal cases prevailing in the court, except a Brazilian drug trafficking case. DoJ was granted a court order to force Apple to create a special version of iOS that could defeat the encryption on a seized iPhone 5C belongs to one of the dead terrorists named Syed Rizwan Farook. Apple is also fighting one such court order with the Federal Bureau of Investigation (FBI)
Source: https://thehackernews.com/2016/03/whatsapp-encryption.html