Reuters
The FBI says 'going dark' with encryption will cause more harm than good.
Encryption is a security technology that scrambles digital information using specialist mathematics. It makes it so only people in possession of a specific unlock key or password can read the encrypted information.
Encryption is used by several technology companies including Microsoft, Facebook, Google and Apple and is often viewed as a key way people can protect their digital privacy.
However, Comey attacked the technology in a public op-ed, where he claimed a move towards end-to-end encryption could benefit terrorist groups, more than general web users.
"I really am not a maniac (or at least my family says so). But my job is to try to keep people safe. In universal strong encryption, I see something that is with us already and growing every day that will inexorably affect my ability to do that job," he said.
"The logic of encryption will bring us, in the not-too-distant future, to a place where devices and data in motion are protected by universal strong encryption. There are many costs to this."
The FBI director highlighted terrorist groups', such as the Islamic State (ISIS), use of encrypted online services as proof of his claim:
"That tension is vividly illustrated by the current ISIL [also known as ISIS] threat, which involves ISIL operators in Syria recruiting and tasking dozens of troubled Americans to kill people, a process that increasingly takes part through mobile messaging apps that are end-to-end encrypted.
"There is simply no doubt that bad people can communicate with impunity in a world of universal strong encryption."
Comey's comments follow widespread concerns about attempts by US government agencies to subvert encryption.
Der Spiegel reported the NSA's specialist Office of Target Pursuit maintains a team of engineers with the aim of cracking into encrypted services in December 2014.
The US government is also considering proposals that would let agencies like the NSA and FBI legally collect and decrypt data from smartphones and "other communications devices."
A group of 140 companies, including Google, Microsoft, Apple and Facebook sent an open letter to President Obama in May urging him to reject the encryption proposals, fearing they would damage the US economy.
UK prime minister David Cameron has also hinted at similar plans to hamper the use of encryption. Cameron told Parliament he wants to "ensure that terrorists do not have a safe space in which to communicate," on June 6.
The details of Cameron's plans remain unknown, though many security professionals, including cryptography expert Bruce Schneier, have argued blocking, or controlling the use of encryption, is impossible.