Former GCHQ director Robert Hannigan has spoken out against building backdoors into end-to-end encryption (e2) schemes as a means to intercept communications by terrorists and other ne'er do wells.

UK Home Secretary Amber Rudd has criticised mobile messaging services such as WhatsApp, that offer end-to-end encryption in the wake of recent terror outages, such as the Westminster Bridge attack, arguing that there should be no place for terrorists to hide.

Hannigan, who led GCHQ between November 2014 and January 2017, struck a different tone in an interview with BBC Radio 4 flagship news programme Today on Monday morning, arguing there's no simple answer on the national security challenges posed by encryption.

"Encryption is overwhelmingly a good thing," Hannigan said. "It keeps us all safe and secure. Throughout the Cold War and up until 15 years ago it was something only governments could do at scale."

The former spy agency boss described the availability of e2e encryption in smartphone apps available to everyone is, broadly, a good thing.

"The challenge for governments is how do you stop the abuse of that encryption by the tiny amount of people who want to do bad things, like terrorists and criminals," Hannigan said.

"You can't un-invent end-to-end encryption… you can't legislate it away," he added.

The former head of GCHQ favours co-operation between government agencies and private (tech) companies "to find a way around it" rather than passing laws that oblige tech providers to weaken the encryption of their technology or install backdoors.

"I don't advocate building in backdoors," Hannigan said. "It's not a good idea to weaken security for everybody in order to tackle a minority.

The best solution is to "target the people who are abusing" encryption systems and go after the smartphone or laptops they are using.

"Trying to weaken the system, trying to build in backdoors won't work and is technically difficult," Hannigan reiterated.

e2e schemes are a subset of encryption in general but present a tougher challenge for law enforcement and government because service provides don't hold the private keys needed to decipher data.

Not all encryption works end to end. As well as malware implants on end point devices, encryption schemes can be broken through protocol weakness and implementation flaws.

Hannigan referenced the 1980s Clipper Chip debacle in saying he doesn't think legislation to weaken crypto would work now either. "The Americans tried that in the 1990s under the Clinton Administration and it didn't work. I can't see, particularly since most of these companies are US based, that legislation is the answer."

The co-operation Hanningan advocates with tech firms is more difficult after the revelations from former NSA sysadmin Edward Snowden. This is not just because of pressure from consumers for tech firms to offer technologies more resistant against government snooping but because firms, such as Google, who co-operate with the US government in handing over data under schemes such as PRISM were angered to discover that the NSA was pulling other tricks such as hacking into links between their data centre too.

Telcos, in particular, co-operated with law enforcement agencies across the world in lawful interception schemes for years before smartphones and endpoint devices rather than telecom switches became the necessary focus of surveillance efforts as the result of advances in technology such as the rise of mobile messaging and apps such as WhatsApp, Apple iMessage and Telegram, among others.

The former GCHQ boss - who started off his tenure criticising tech giants for acting as a "command and control" networks of choice for terrorists and criminals back in November 2014 - underwent something of a conversion in attitudes as a spy agency boss.

By March 2016 he was had softened his stance and begun advocating co-operation with tech giants, such as Google and Apple, a line he expanded and updated during his interview on Monday morning, which is well worth a listen.

Hanningan also wants technology firms to get together and apply their "engineering brilliance" to tackle the abuse of the internet as a vehicle for spreading terrorist propaganda and radicalisation. "Legislation is a blunt last resort," he said.

Lastly, in a wide-ranging interview, Hanningan said Russia as a country was responsible for a "disproportionate amount of mayhem in cyberspace" such as attacks on democratic institutions as well as the activities of cyber-criminal groups. He praised the creation of the UK's National Cyber Security Centre (NCSC) in improving defences ("the private sector needs to get better") as well as French President Emmanuel Macron's public condemnation as positive moves in combating the problem. Hanningan went on to suggest that sanctions and other measures against Russia over cyber espionage might be necessary to set "red lines" while acknowledging much online malfeasance comes from cybercrime elements.

"There is an overlap of crime and state and a deeply corrupt system that allows crime to flourish. But the Russian state could do a lot to stop that and it can certainly rein in its own activity," Hanningan concluded. ®