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Background: Telegram is a secured messaging app, similar to many others (WhatsApp, Signal, ...). It emphasizes its security features and has become (like a few others) a way for people to exchange messages in a secured way. "People" can be good or bad, depending on personal interpretation.

An article by Gordon Ryner in The Telegraph (27/03/2017) mentions that

Rival [to WhatsApp] messaging services such as Telegram are also encrypted, but their software has been written to enable law enforcement agencies to access messages where they can prove it is a necessary part of a criminal investigation.

Police in Germany knew Anis Amri was planning a suicide attack nine months before he drove a lorry into a packed Christmas market in Berlin last December, killing 12, because they had been able to access encrypted Telegram messages.

(emphasis and clarification mine)

The article is generally poorly written (the author mixes up all kind of communication channels without understanding the differences), the quoted piece, however, suggests that Telegram is not as protective of the user data they control (= stored and encrypted by them, as opposed to secret chats) as advertized.

Specifically, the FAQ for Telegram states that

The relevant decryption keys are split into parts and are never kept in the same place as the data they protect. As a result, several court orders from different jurisdictions are required to force us to give up any data.

Thanks to this structure, we can ensure that no single government or block of like-minded countries can intrude on people's privacy and freedom of expression. Telegram can be forced to give up data only if an issue is grave and universal enough to pass the scrutiny of several different legal systems around the world.

The important part is

To this day, we have disclosed 0 bytes of user data to third parties, including governments.

(again, emphasis is mine)

There is an obvious contradiction between the journalist statements and Telegram.

While the author of the article is not competent in the matter of encryption and how the messaging apps work, his mention of the specific case of the attack in Germany is worrisome. I could not find sources for his claims (and he does not cite any), only vague CNN or DW mentions of Telegram being used.

Are there any precise information on how the Telegram information was acquired?

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    Side note: The Telegram programmers partially 'rolled their own crypto'. That is a repeating criticism in the security industry about the app, because that is generally considered less secure (plenty of examples around). So alternatively, the program could've been hacked - that may be part of the confusion. – Jan Doggen Mar 29 '17 at 10:23
  • @JanDoggen: this is a complicated subject. A question on Information Security SE discusses this BUT one has to read ALL of teh comments and answers to have an up-to-date status (the accepted answer is not relevant anymore). As for hacking, they have a contest and Telegram is partially open-sourced (fully for the parts relevant to "secret chats") – WoJ Mar 29 '17 at 10:33
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As far as we know, the police did not go to Telegram and ask them for the data.

Vice (Germany) states - based on non-public papers by the LKA - that the police got the data directly from the phone via lawful interception. They also state that no other information is public, but they speculate that the data was retrieved via Account-Hijacking:

Doch wie genau konnten die Ermittler die Telegram-Chats von Anis Amri abhören? Aus den Papieren des nordrhein-westfälischen LKAs geht dies nicht eindeutig hervor. In den Unterlagen, deren zentrale Passagen Motherboard kennt, steht lediglich, dass das LKA im Rahmen einer üblichen Telekommunikationsüberwachung gehandelt habe. Doch technisch gesehen gibt es nur eine Möglichkeit, was das bedeutet: Die Ermittler nutzten den Trick des sogenannten Account-Hijackings. My translation: But how could the investigators listen to the Telegram chats? This is not clear from the papers of the LKA. In the papers - whose central passages are known to Motherboard [Vice], it only says that the LKA acted in the frame of a normal Telekommunikationsüberwachung [lawful interception]. But from a technical view, there is only one way to achieve this: Investigators used the trick of so called account-highjacking [The article goes on describing what account-highjacking is]

Note also that your quote seems to misrepresent the Telegram FAQ. Telegram states that they do not store end-to-end keys on their server, so they cannot decrypt these messages even if asked (at least if they are truthful in their FAQ). They store the keys for data the user doesn't encrypt end-to-end on their servers though (obviously).

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    Telegram does store keys on their servers for "normal" messages. This is stated in the FAQ I quoted (the keys are split between several datacenters). Only if you go into "secret chat" mode no keys are stored by Telegram. This is explicit in their FAQ (the portion I quoted was about the keys they store, which is the only way to access the massages from Telegram in the context of the case i mention) – WoJ Mar 29 '17 at 8:35
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    @WoJ Right, but that's how it should be. "secret chat" is end-to-end encrypted, while "normal" chat is not. And when you don't end-to-end encrypt, you need to store the keys somewhere where you as the provider have access to. The downside of end-to-end is obviously that you can only access the messages from this one device (which is why Telegram offers both modes). This is clearly stated by Telegram. Either way, Telegram doesn't seem to have given any key to the police in this case. – tim Mar 29 '17 at 8:39
  • of course this is clearly stated by Telegram and I have never claimed otherwise. My question is about Telegram providing data to the police. This can be done only with the data they have encryption keys for (as mentioned in my question and pointing to their FAQ where they explain how these requests are handled). I honestly do not understand how I "severely misrepresented the Telegram FAQ" (a product which I like BTW) – WoJ Mar 29 '17 at 8:45
  • @WoJ Ok, "severely" is maybe stated a bit too strong, but you at least implied that this case shows something new about Telegram security ("the quoted piece, however, suggests that Telegram is not as hermetic as advertized", which only makes sense if it means that end-to-end keys are revealed). This doesn't seem the case to me. End-to-end keys are not and cannot be revealed (if we trust Telegram), and normal keys obviously need to be stored and can be subject to lawful requests. – tim Mar 29 '17 at 8:52
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    not new but unusual. Telegram states "no data were ever released", journalists state "Telegram released data". I work in information security so the technical security part is clear. the "what we say vs what we do" was not but your answer strongly suggests that the data was retrieved on the device and not from telegram (= the article claim is bogus). I will reword the "hermetic" part to clarify. – WoJ Mar 29 '17 at 8:56

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