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I am looking for an app (or other method) to securely message my friends on other mobile devices.

Specifically:

  • use on different operating systems (Android and iOS)
  • group conversations
  • encryption (eg. end-to-end encryption)
  • protection against MITM attacks
  • open source (so that it can be audited by anyone)
  • Could you explain what you mean with "securely"? – unor Nov 12 '14 at 13:14
  • @unor: End-to-end encryption, and the likes ... – gartenriese Nov 12 '14 at 14:54
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I recently switched from Whatsapp to Telegram, mainly because it has self destructing messages, but the features you want, and extra are also here:

  • Android and iOS and Windows Phone and OSX and Linux
  • End-to-end encryption1
  • Group chats (up to 200 people)
  • Free, no subscriptions, no ads
  • Uses phone numbers (like Whatsapp)
  • Over the internet
  • Use on multiple devices (unlike Whatsapp)
  • Send self-destructing messages (in secret chats, see below)
  • Mostly open source

1End-to-end encryption:

In Telegram, there are 2 types of chats - normal chat, and secret chat.

Normal chat: data is in the cloud, encrypted

Secret chat: data does not stay in the cloud once delivered; end-to-end encryption; Diffie-Helman Key Exchange

If you want to know more about the technical details, see the FAQ for the Technically Inclined, or just the regular FAQ.

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    Don't rely on "self-destructing messages", anyone can take a screenshot or even a picture of the phone with a camera – user2813274 Nov 13 '14 at 2:18
  • After reading this I'm not so sure it's that secure. – gartenriese Nov 13 '14 at 6:43
  • @user2813274 True, but that was just a plus point. – ᔕᖺᘎᕊ Nov 13 '14 at 7:19
  • @gartenriese it's your choice in the end, if you wanted protection from the government, you should have said so in the question. This is a very secure messaging app if you use the secret chat, with E-E encryption, as you said in your comment you wanted. – ᔕᖺᘎᕊ Nov 13 '14 at 7:24
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    here is a comparison: eff.org/secure-messaging-scorecard, Telegram lacks some security features – Gabor Nov 14 '14 at 19:42
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You can try ChatSecure - https://chatsecure.org/. It offers end to end encryption via OTR. It is open source and available both on iOS and Android. Group chat encryption is dependent if your XMPP server provider offers or enforces encrypted connection to it's clients, most XMPP servers support it. If you are unsure, you can test a server at xmpp.net.

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    Does it support "group conversations"? – Izzy Nov 12 '14 at 17:16
  • I tried ChatSecure and the group chat didn't seem to be encrypted, only the 1-on-1 chats. – gartenriese Nov 13 '14 at 6:47

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