* Encrypted messaging app to be deployed by summer

* Goal is to secure conversations between officials

* Macron's circle had grown fond of the Telegram app

By Mathieu Rosemain

PARIS, April 16 (Reuters) - The French government is building its own encrypted messenger service to ease fears that foreign entities could spy on private conversations between top officials, the digital ministry said on Monday.

None of the world's major encrypted messaging apps, including Facebook's WhatsApp and Telegram - a favourite of President Emmanuel Macron - are based in France, raising the risk of data breaches at servers outside the country.

About 20 officials and top civil servants are testing the new app which a state-employed developer has designed, a ministry spokewoman said, with the aim that its use will become mandatory for the whole government by the summer.

"We need to find a way to have an encrypted messaging service that is not encrypted by the United States or Russia," the spokeswoman said. "You start thinking about the potential breaches that could happen, as we saw with Facebook, so we should take the lead."

The U.S. social network, which bought WhatsApp in 2014, has drawn heavy criticism since it acknowledged that information about many millions of users wrongly ended up in the hands of political consultancy Cambridge Analytica.

The French government's encrypted app has been developed on the basis of free-to-use code found on the Internet and could be eventually made available to all citizens, the spokeswoman said. She declined to give the names of either the codes or the messaging service.

FOND OF TELEGRAM

Macron's inner circle - now government advisers or ministers - have grown fond of the Telegram app, which they used to plot his rise to power and his presidential election campaign last year.

Macron, an economy minister in the previous Socialist administration, wanted at the time to use an encrypted messaging service that even his rivals in the last government could not crack, a close adviser to Macron told Reuters.

Since then, most of his lawmakers have joined the app and the president himself can often be seen online on Telegram, sometimes in the early hours of the morning..

But privacy concerns started growing earlier this year, and security tools from French security firm Thales installed on officials' work smartphones prevented the use of either WhatsApp or Telegram.

Telegram was set up by a Russian entrepreneur who has come into conflict with the authorities. Russia's state telecommunications regulator said on Monday it had begun blocking access to Telegram after the company refused to comply with an order to give state security access to its users' secret messages.

Both WhatsApp and Telegram promote themselves as ultra secure because all their data is encrypted from start to finish. WhatsApp relies on open industry standards created by the developers behind Signal, a rival messaging app, while Telegram relies on its own, home-grown encryption techniques. (Additional reporting by Michel Rose and Myriam Rivet Editing by Ingrid Melander and David Stamp)

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