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A group chat cannot be E2E encrypted, or new members would not be able to see previous messages. So, this should demonstrate to you that Telegram private group

A group chat cannot be E2E encrypted, or new members would not be able to see previous messages. So, this should demonstrate to you that Telegram private group chats are not E2EE.

rightbyte 2y ago
> A group chat cannot be E2E encrypted, or new members would not be able to see previous messages. Why? Any member of the group can send the messages to the newcomer. Not that I trust closed and centralized services anyways. But it should be possible.
- tmottabr 2y ago
  New messages yes, but old messages no.. The typical way group chat encryption is done is the client generate a key per message, it use that key to encrypt the content of that single message. Then it will encrypt the message key with personal key for each member of the group, and it can only do that for current members of the group. Once you receive a message the client will use your personal key to decrypt the copy of the message key encrypted with it, then use the message key to decrypt the message. The problem with this is that, first it does not escale, the larger the group gets the harder it is to encrypt the messages because you need to encrypt the message key with more and more personal keys, this make the work load bigger and the message size bigger as well. Telegram support very large groups that make encrypting groups not practical. Also Telegram allow you to see older messages sent before you join the group as those get stored in the servers, if you join the group later then for older messages the per message key will not have being encrypted with your personal key so you cannot decrypt it, thus cannot decrypt the message. You would need to either store the per message key unencrypted in the server and make encryption useless as the server would be able to decrypt it, have the client from some older member of the group re-encrypt the per message key for older messages and send to new members or the simpler approach that Telegram took to not encrypt it at all.
  - foldr 2y ago
    You're overcomplicating it. The existing members of the group have the plaintext of the older messages. So they can totally send those messages to new members of the group. If I can copy/paste the history of the group chat and send it to a new group member, then the application itself can do the equivalent behind the scenes.
    - 0points 2y ago
      Sure, but that would defeat the purpose of the encryption since anyone could join at a later date and have other clients snitch out whatever was said in the past. Might as well use Telegram at that point ^_^
      - foldr 2y ago
        In a public group that anyone can join without an invite it’s unclear why you’d even want E2E in the first place, so we’re presumably talking about invite-only groups. In that case, sending old messages to new members may or may not be a desired behavior, but it doesn’t defeat the purpose of E2E.
- 0points 2y ago
  Because of how E2EE is implemented, data must be encrypted for you to decrypt. This can't work after the fact for obvious reasons.
exe34 2y ago
> or new members would not be able to see previous messages. that's a feature.
fsflover 2y ago
> or new members would not be able to see previous messages On Matrix it's somehow not a problem.
Moldoteck 2y ago
yeah, signal/ws/matrix don't have e2ee group chats... oh wait, they have...
- a_dabbler 2y ago
  I assume they mean that Telegram does not have the option to have encrypted E2E chats not that it isn't possible to implement
  - Moldoteck 2y ago
    "or new members would not be able to see previous messages." - this sounds more like he really thought group chats can't be e2ee
- tmottabr 2y ago
  They have, but the limit of people in a group is significant lower then Telegram, at least for signal\ws, dont know how matrix handle this. Telegram allow 200000 members in a chat group. Signal on the other hand allow only 1000 and ws limit is 1024. It is possible to have group chat encrypted, but this does not scale very well and allowing new members to see older messages also is trick, although both are possible. EDIT: i just checked for matrix and while they do not impose an limit their docs do indicate that there are performance problems for very large groups with tens of thousands of members, that while much bigger then signal\ws it is still much smaller compared to telegram.

A group chat cannot be E2E encrypted, or new members would not be able to see previous messages. So, this should demonstrate to you that Telegram private group chats are not E2EE.

rightbyte 2y ago

> A group chat cannot be E2E encrypted, or new members would not be able to see previous messages. Why? Any member of the group can send the messages to the newcomer. Not that I trust closed and centralized services anyways. But it should be possible.

tmottabr 2y ago
New messages yes, but old messages no.. The typical way group chat encryption is done is the client generate a key per message, it use that key to encrypt the content of that single message. Then it will encrypt the message key with personal key for each member of the group, and it can only do that for current members of the group. Once you receive a message the client will use your personal key to decrypt the copy of the message key encrypted with it, then use the message key to decrypt the message. The problem with this is that, first it does not escale, the larger the group gets the harder it is to encrypt the messages because you need to encrypt the message key with more and more personal keys, this make the work load bigger and the message size bigger as well. Telegram support very large groups that make encrypting groups not practical. Also Telegram allow you to see older messages sent before you join the group as those get stored in the servers, if you join the group later then for older messages the per message key will not have being encrypted with your personal key so you cannot decrypt it, thus cannot decrypt the message. You would need to either store the per message key unencrypted in the server and make encryption useless as the server would be able to decrypt it, have the client from some older member of the group re-encrypt the per message key for older messages and send to new members or the simpler approach that Telegram took to not encrypt it at all.
- foldr 2y ago
  You're overcomplicating it. The existing members of the group have the plaintext of the older messages. So they can totally send those messages to new members of the group. If I can copy/paste the history of the group chat and send it to a new group member, then the application itself can do the equivalent behind the scenes.
  - 0points 2y ago
    Sure, but that would defeat the purpose of the encryption since anyone could join at a later date and have other clients snitch out whatever was said in the past. Might as well use Telegram at that point ^_^
    - foldr 2y ago
      In a public group that anyone can join without an invite it’s unclear why you’d even want E2E in the first place, so we’re presumably talking about invite-only groups. In that case, sending old messages to new members may or may not be a desired behavior, but it doesn’t defeat the purpose of E2E.
0points 2y ago
Because of how E2EE is implemented, data must be encrypted for you to decrypt. This can't work after the fact for obvious reasons.

exe34 2y ago

> or new members would not be able to see previous messages. that's a feature.

fsflover 2y ago

> or new members would not be able to see previous messages On Matrix it's somehow not a problem.

Moldoteck 2y ago

yeah, signal/ws/matrix don't have e2ee group chats... oh wait, they have...

a_dabbler 2y ago
I assume they mean that Telegram does not have the option to have encrypted E2E chats not that it isn't possible to implement
- Moldoteck 2y ago
  "or new members would not be able to see previous messages." - this sounds more like he really thought group chats can't be e2ee
tmottabr 2y ago
They have, but the limit of people in a group is significant lower then Telegram, at least for signal\ws, dont know how matrix handle this. Telegram allow 200000 members in a chat group. Signal on the other hand allow only 1000 and ws limit is 1024. It is possible to have group chat encrypted, but this does not scale very well and allowing new members to see older messages also is trick, although both are possible. EDIT: i just checked for matrix and while they do not impose an limit their docs do indicate that there are performance problems for very large groups with tens of thousands of members, that while much bigger then signal\ws it is still much smaller compared to telegram.