That's the message behind a new document created by the Wisconsin Statewide Information Center, a designated intelligence fusion center, with the Department of Homeland Security's Office of Intelligence and Analysis. The document, which was obtained by The Intercept, is marked For Official Use Only and titled "Going Dark – Covert Messaging Applications and Law Enforcement Implications."

The document, dated Sept. 29, 2015, appears to serve as a primer for law enforcement on encryption, examining various encrypted messaging services, such as Silent Circle, Telegram and Wickr. It notes that increasing "public awareness of government surveillance has contributed to the rising consumer demand for covert messaging apps."

FBI Director James Comey has blasted the growing use of encryption in recent months, claiming simultaneously that it presented an opportunity for terrorists, while also suggesting the FBI could thwart efforts by those people were "going dark."