Terror investigators grapple with Telegram app

The messaging platform's strong encryption makes it a favorite of IS

Smartphone app Telegramfavored by the Islamic State group thanks to the encrypted messaging it offersis proving a headache for French anti-terror investigators.

The free-to-download instant messengerwhich allows people to exchange messagesphotos and videos in groups of up to 5,000 peoplehas attracted some 100 million users since its launch in 2013.

And there are a couple of features that make it particularly attractive to jihadistswho cannot only rest assured that their private messages are out of the reach of intelligence officialsbut can disperse propaganda on YouTube-like public channels.

After IS gunmen and suicide bombers massacred 130 people in Paris in NovemberTelegram blocked dozens of public channels that were being used to spread extremist messages.

But Russian internet guru Pavel Durovwho founded Telegram with his brother Nikolaiinsisted that not even he has the power to intercept users' private chats.

In Francewhich has suffered a string of further jihadist assaults since the Paris carnageinvestigators are still dealing with the fallout from the communications of an IS member suspected of using Telegram to direct people to carry out attacks.

Rachid Kassima 29-year-old Frenchman who has regularly appeared in IS propaganda videos shot in Syria or Iraqwas able to urge some 300 contacts to commit attacks on home soilnotably publishing a list of targets and scenarios for how to carry them out.

Among his contacts were Larossi Abballawho knifed to death a senior policeman and his partner in the Parisian suburbs in Juneand two teenage jihadists who slit the throat of an elderly priest in a northern French church in July.

Kassim has been back in the news this week after it emerged that female jihadists suspected of plotting to blow up a car filled with gas canisters near Paris' Notre Dame cathedral were on his contact list.

Unable to get past Telegram's impenetrable encryptionthe best intelligence officials can hope for is to sneak into extremist chat rooms by posing as jihadists - but they're bound to attract suspicion unless they talk the talk convincingly.

"Infiltrating is possiblebut you have to be a good actor and have a lot of cultural and religious awareness to get away with it," one investigator said.

So confident is Telegram in its encryptionit has offered up to $300,000 to anyone who manages to crack its system.

Moreoverthe app has a feature that allows users to set messages to auto-destructmaking it impossible to recover them later for use in investigations.

Even in the realm of public jihadist propaganda on Telegramit is "practically impossible to track the millions of messages that are exchanged every hour"one investigator lamented.

French intelligence chief Patrick Calvar described the app in May as "the main network used by terrorists".

"We bump into encryption problems on a daily basisas the means of communication multiply along with the amount of data that we have to gather," he saidadding that encryption is "a major question that only international conventions can decide on".

The use of such appswhich soared after Edward Snowden's revelations of mass US surveillance in 2013has sparked debate over the balance between internet users' right to privacy and the need for security agencies to protect the public.