FBI chief wants 'backdoor access' to encrypted communications to fight Isis

Experts warn that 'magical thinking' of a security flaw only the US government could exploit could easily be utilized by hackers, foreign spies and terrorists

The director of the Federal Bureau of Investigation has warned US senators that the threat from the Islamic State merits a "debate" about limiting commercial encryption - the linchpin of digital security - despite a growing chorus of technical experts who say that undermining encryption would prove an enormous boon for hackers, cybercriminals, foreign spies and terrorists.

In a twin pair of appearances before the Senate's judiciary and intelligence committees on Wednesday, James Comey testified that Isis's use of end-to-end encryption, whereby the messaging service being used to send information does not have access to the decryption keys of those who receive it, helped the group place a "devil" on the shoulders of potential recruits "saying kill, kill, kill, kill".