The cellphone encryption technology used most widely across the world can be easily defeated by the National Security Agency, an internal document shows, giving the agency the means to decode most of the billions of calls and texts that travel over public airwaves every day.

While the military and law enforcement agencies long have been able to hack into individual cellphones, the NSA’s capability appears to be far more sweeping because of the agency’s global signals collection operation. The agency’s ability to crack encryption used by the majority of cellphones in the world offers it wide-ranging powers to listen in on private conversations.