Telegram
Telegram is a non-profit[13][14] cloud-basedinstant messaging service. Telegram clientapps exist for Android, iOS, Windows Phone,Windows NT, macOS and Linux.[12] Users can send messages and exchange photos, videos, stickers, audio and files of any type.
Telegram was founded by the Russianentrepreneur Pavel Durov.[15] Its client-side code is open-source software but the source code for recent versions is not always immediately published,[16] whereas its server-side code is closed-source and proprietary.[17]The service also provides APIs to independent developers. In February 2016, Telegram stated that it had 100 million monthly active users, sending 15 billion messages per day. According to its CEO, as of April 2017, Telegram has more than 50% annual growth rate.[18]
Telegram's security model has received notable criticism by cryptography experts.[who?] They have argued that it is undermined by its use of a custom-designed encryption protocol that has not been proven reliable and secure, by storing all messages on their servers by default and by not enablingend-to-end encryption for messages by default. Pavel Durov has argued that this is because it helps to avoid third-party unsecure backups and to allow users to access messages and files from any device.[19]Messages in Telegram are server-client encrypted by default,[20] and the service provides end-to-end encryption for voice calls[21] and optional end-to-end encrypted "secret" chats.[22]
History
Development
Telegram was launched in 2013 by the brothers Nikolai and Pavel Durov, who had previously founded the Russian social network VK, but had to leave the company after it was taken over by the Mail.ru Group.[23][24] Nikolai Durov created theMTProto protocol that is the basis for the messenger, while Pavel provided financial support and infrastructure through his Digital Fortress fund with business partner Axel Neff, a third founder of Telegram.[25]
Telegram is registered as both an EnglishLLP[26] and an American LLC.[27] It does not disclose where it rents offices or which legal entities it uses to rent them, citing the need to "shelter the team from unnecessary influence" and protect users from governmental data requests.[28] Pavel Durov has said that the service was headquartered in Berlin, Germany, in 2015[29] and early 2015, but moved to different jurisdictions after failing to obtain residence permits for everyone on the team.[30] Durov left Russia and is said to be moving from country to country with a small group of computer programmers.[23]According to press reports, Telegram had employees in St. Petersburg.[30] The Telegram team is currently based in Dubai.[31]
On 22 December Anton Rozenberg, a former employee of Telegram’s publishing division Telegraph posted on Facebook what he claims is an advertorial video for the new platform (he did not disclose the source of the video). According to sources familiar with the matter Telegram will launch its own Blockchain platform and cryptocurrency. The new platform will be dubbed either “The Open Network” or “Telegram Open Network” (TON) and is supposed to be based on an improved version of Blockchain technology. Cointelegraph stated that the currency of TON will be called “Gram” and the platform will be natively integrated with many of the most popular messaging apps (it’s not yet certain which ones). The platform will utilize light wallets, making it unnecessary for users to download a large and unwieldy Blockchain.[32]
Usage numbers
In October 2013, Telegram had 100,000 daily active users.[24] On 24 March 2014, Telegram announced that it had reached 35 million monthly users and 15 million daily active users.[33] In October 2014, South Korean governmental surveillance plans drove many of its citizens to switch to Telegram.[29] In December 2014, Telegram announced they had 50 million active users, generating 1 billion daily messages and that they had 1 million new users signing up on their service every week;[34] traffic doubled in five months with 2 billion daily messages.[35] In September 2015, an announcement stated that the app had 60 million active users and delivered 12 billion daily messages.[36] In February 2016, Telegram announced that they had 100 million monthly active users, with 350,000 new users signing up every day, delivering 15 billion messages daily.[37] In December 2017, Telegram reached 180 million monthly active users.[31]
Features
Account
Telegram accounts are tied to telephone numbers and are verified by SMS or phone call.[38] Users can add multiple devices to their account and receive messages on each one. Connected devices can be removed individually or all at once. The associated number can be changed at any time and when doing so, the user's contacts will receive the new number automatically.[38][39][40] In addition, a user can set up an alias that allows them to send and receive messages without exposing their phone number.[41] Telegram accounts can be deleted at any time and they are deleted automatically after six months of inactivity by default, which can optionally be changed to 1 month and 12 months. Users can replace exact "last seen" timestamps with broader messages such as "last seen recently".[42]
The default method of authentication that Telegram uses for logins is SMS-based single-factor authentication.[43][44] All that is needed in order to log into an account and gain access to that user's cloud-based messages is a one-time passcode that is sent via SMS to the user's phone number.[44][45] These login SMS messages are known to have been intercepted in Iran, Russia and Germany, possibly in coordination with phone companies.[45][46][47] Pavel Durov has said that Telegram users in "troubled countries" should enable two-factor authentication by creating passwords, which Telegram allows, but does not require.[45][46]
Cloud-based messages
Telegram's default messages are cloud-based and can be accessed on any of the user's connected devices. Users can share photos, videos, audio messages and other files (up to 1.5 gigabyte in size). Users can send messages to other users individually or to groups of up to 30,000 members.[48] Sent messages can be edited and deleted on both sides within 48 hours after they have been sent. This gives user an ability to correct typos and retract messages that were sent by mistake.[49] The transmission of messages to Telegram Messenger LLP's servers is encrypted with the service's MTProto protocol.[50] According to Telegram's privacy policy, "all data is stored heavily encrypted and the encryption keys in each case are stored in several other DCs in different jurisdictions. This way local engineers or physical intruders cannot get access to user data".[51] This makes the messages' security roughly comparable to that of e-mail. Here, most providers employ client-server encryption as well, however usually with the standardized protocol Transport Layer Security. E-mails may or may not be encrypted on the servers. Telegram cloud messages and media remain on the servers at least until deleted by all participants.
Bots
In June 2015, Telegram launched a platform for third-party developers to create bots.[52]Bots are Telegram accounts operated by programs. They can respond to messages ormentions, can be invited into groups and can be integrated into other programs. Dutch website Tweakers reported that an invited bot can potentially read all group messages when the bot controller changes the access settings silently at a later point in time. Telegram pointed out that it considered implementing a feature that would announce such a status change within the relevant group.[53] Also there are inline bots, which can be used from any chat screen. In order to activate an inline bot, user needs to type in the message field a bot's username and query. The bot then will offer its content. User can choose from that content and send it within a chat.[54]
Channels
Channels can be created for broadcasting messages to an unlimited number of subscribers.[55] Channels can be publicly available with an alias and a permanent URL so anyone can join. Users who join a channel can see the entire message history. Each message has its own view counter, showing how many users have seen this message. Users can join and leave channels at any time. Furthermore, users can mute a channel, meaning that the user will still receive messages, but won't be notified.
Stickers
Stickers are cloud-based, high-definition images intended to provide more expressiveemoji. When typing in an emoji, the user is offered to send the respective sticker instead. Stickers come in collections called "sets", and multiple stickers can be offered for one emoji. Telegram comes with one default sticker set,[56] but users can install additional sticker sets provided by third-party contributors. Sticker sets installed from one client become automatically available to all other clients. Sticker images use WebP file format, which is better optimized to be transmitted over internet.
Drafts
Drafts are unfinished messages synced across user devices. One can start typing a message on one device and continue on another. The draft will persist in editing area on any device until it is sent or removed.[57]
Secret chats
A "secret chat" confirmation notice - screenshot from Android Marshmallow.
Messages can also be sent with client-to-client encryption in so-called secret chats. These messages are encrypted with the service's MTProto protocol.[58] Unlike Telegram's cloud-based messages, messages sent within a secret chat can be accessed only on the device upon which the secret chat was initiated and the device upon which the secret chat was accepted; they cannot be accessed on other devices.[24][50][59]Messages sent within secret chats can, in principle, be deleted at any time and can optionally self-destruct.[60]
Secret chats have to be initiated and accepted by an invitation, upon which the encryption keys for the session are exchanged. Users in a secret chat can verify that no man-in-the-middle attack has occurred by comparing pictures that visualize their public key fingerprints.[61]
According to Telegram, secret chats have supported perfect forward secrecy since December 2014. Encryption keys are periodically changed after a key has been used more than 100 times or has been in use for more than a week.[62] Old encryption keys are destroyed.[39][40][63]
Windows and Linux users are still not able to use secret chats using the official Telegram Desktop app while the official macOS-only client supports them.[64]
Secret chats are not available for groups or channels.
Telegram's local message database is not encrypted by default.[62] Some Telegram clients allow users to encrypt the local message database by setting a passphrase.[65]
Voice calls
In the end of March 2017, Telegram introduced its own voice calls. The calls are built upon the end-to-end encryption of Secret Chats. Connection is established as peer-to-peer whenever possible, otherwise the closest server to the client is used. According to Telegram, there is a neural network working to learn various technical parameters about call to provide better quality of the service for future uses. After a brief initial trial in Western Europe, voice calls are now available for use in most countries.[66]
Architecture
Encryption scheme
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A simplified illustration of the MTProto encryption scheme.
Telegram uses a symmetric encryptionscheme called MTProto. The protocol was developed by Nikolai Durov and other developers at Telegram and is based on 256-bit symmetric AES encryption, 2048-bit RSAencryption and Diffie–Hellman key exchange.[58]
Servers
Telegram Messenger LLP has servers in a number of countries throughout the world to improve the response time of their service.[67]Telegram's server-side software is closed-source and proprietary. Pavel Durov has said that it would require a major architectural redesign of the server-side software to connect independent servers to the Telegram cloud.[68]
Client apps
Telegram has various client apps. This list includes versions developed on official platforms backed by Telegram Messenger LLP and unofficial clients that are developed by the community. The source code of all official Telegram clients (and some of the unofficial clients) is open source and released under the GNU General Public Licenceversion 2 or 3.
Users can also access Telegram's cloud-based messages via an official web browserinterface called Telegram Web (aka Webogram). Users can share images, files and emoticons with previously-added contacts; this works in most modern browsers, such as Firefox, Safari, and Google Chrome.[75][82]
APIs
Telegram has public APIs with which developers can access the same functionality as Telegram's official apps to build their own messaging applications.[89] In February 2015, creators of the unofficial Whatsapp+ client released the Telegram Plus app, later renamed to Plus Messenger, after their original project got a cease-and-desist orderfrom WhatsApp.[90][91] In September 2015,Samsung released a messaging application based on these APIs.[92]
Telegram also offers an API that allows developers to create bots, which are accounts controlled by programs.[93][94] In February 2016, Forbes launched an AI-powered news bot that pushes popular stories to subscribers and replies to search queries with relevant articles.[95] TechCrunch launched a similar bot in March 2016.[96]
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