By the time you scan the QR code,
inviter may not be in the group already.
In this case securejoin protocol will never complete.
If you then join the group in some other way,
this results in you implicitly adding that inviter
to the group.
Follow-up for https://github.com/chatmail/core/pull/7042, part of
https://github.com/chatmail/core/issues/6884.
This will make it possible to create invite-QR codes for broadcast
channels, and make them symmetrically end-to-end encrypted.
- [x] Go through all the changes in #7042, and check which ones I still
need, and revert all other changes
- [x] Use the classical Securejoin protocol, rather than the new 2-step
protocol
- [x] Make the Rust tests pass
- [x] Make the Python tests pass
- [x] Fix TODOs in the code
- [x] Test it, and fix any bugs I find
- [x] I found a bug when exporting all profiles at once fails sometimes,
though this bug is unrelated to channels:
https://github.com/chatmail/core/issues/7281
- [x] Do a self-review (i.e. read all changes, and check if I see some
things that should be changed)
- [x] Have this PR reviewed and merged
- [ ] Open an issue for "TODO: There is a known bug in the securejoin
protocol"
- [ ] Create an issue that outlines how we can improve the Securejoin
protocol in the future (I don't have the time to do this right now, but
want to do it sometime in winter)
- [ ] Write a guide for UIs how to adapt to the changes (see
https://github.com/deltachat/deltachat-android/pull/3886)
## Backwards compatibility
This is not very backwards compatible:
- Trying to join a symmetrically-encrypted broadcast channel with an old
device will fail
- If you joined a symmetrically-encrypted broadcast channel with one
device, and use an old core on the other device, then the other device
will show a mostly empty chat (except for two device messages)
- If you created a broadcast channel in the past, then you will get an
error message when trying to send into the channel:
> The up to now "experimental channels feature" is about to become an officially supported one. By that, privacy will be improved, it will become faster, and less traffic will be consumed.
>
> As we do not guarantee feature-stability for such experiments, this means, that you will need to create the channel again.
>
> Here is what to do:
> • Create a new channel
> • Tap on the channel name
> • Tap on "QR Invite Code"
> • Have all recipients scan the QR code, or send them the link
>
> If you have any questions, please send an email to delta@merlinux.eu or ask at https://support.delta.chat/.
## The symmetric encryption
Symmetric encryption uses a shared secret. Currently, we use AES128 for
encryption everywhere in Delta Chat, so, this is what I'm using for
broadcast channels (though it wouldn't be hard to switch to AES256).
The secret shared between all members of a broadcast channel has 258
bits of entropy (see `fn create_broadcast_shared_secret` in the code).
Since the shared secrets have more entropy than the AES session keys,
it's not necessary to have a hard-to-compute string2key algorithm, so,
I'm using the string2key algorithm `salted`. This is fast enough that
Delta Chat can just try out all known shared secrets. [^1] In order to
prevent DOS attacks, Delta Chat will not attempt to decrypt with a
string2key algorithm other than `salted` [^2].
## The "Securejoin" protocol that adds members to the channel after they
scanned a QR code
This PR uses the classical securejoin protocol, the same that is also
used for group and 1:1 invitations.
The messages sent back and forth are called `vg-request`,
`vg-auth-required`, `vg-request-with-auth`, and `vg-member-added`. I
considered using the `vc-` prefix, because from a protocol-POV, the
distinction between `vc-` and `vg-` isn't important (as @link2xt pointed
out in an in-person discussion), but
1. it would be weird if groups used `vg-` while broadcasts and 1:1 chats
used `vc-`,
2. we don't have a `vc-member-added` message yet, so, this would mean
one more different kind of message
3. we anyways want to switch to a new securejoin protocol soon, which
will be a backwards incompatible change with a transition phase. When we
do this change, we can make everything `vc-`.
[^1]: In a symmetrically encrypted message, it's not visible which
secret was used to encrypt without trying out all secrets. If this does
turn out to be too slow in the future, then we can remember which secret
was used more recently, and and try the most recent secret first. If
this is still too slow, then we can assign a short, non-unique (~2
characters) id to every shared secret, and send it in cleartext. The
receiving Delta Chat will then only try out shared secrets with this id.
Of course, this would leak a little bit of metadata in cleartext, so, I
would like to avoid it.
[^2]: A DOS attacker could send a message with a lot of encrypted
session keys, all of which use a very hard-to-compute string2key
algorithm. Delta Chat would then try to decrypt all of the encrypted
session keys with all of the known shared secrets. In order to prevent
this, as I said, Delta Chat will not attempt to decrypt with a
string2key algorithm other than `salted`
BREAKING CHANGE: A new QR type AskJoinBroadcast; cloning a broadcast
channel is no longer possible; manually adding a member to a broadcast
channel is no longer possible (only by having them scan a QR code)
We do not try to delete resent messages
anymore. Previously resent messages
were distinguised by having duplicate Message-ID,
but future Date, but now we need to download
the message before we even see the Date.
We now move the message to the destination folder
but do not fetch it.
It may not be a good idea to delete
the duplicate in multi-device setups anyway,
because the device which has a message
may delete the duplicate of a message
the other device missed.
To avoid triggering IMAP busy move loop
described in the comments
we now only move the messages
from INBOX and Spam folders.
This way, the statistics / self-reporting bot will be made into an
opt-in regular sending of statistics, where you enable the setting once
and then they will be sent automatically. The statistics will be sent to
a bot, so that the user can see exactly which data is being sent, and
how often. The chat will be archived and muted by default, so that it
doesn't disturb the user.
The collected statistics will focus on the public-key-verification that
is performed while scanning a QR code. Later on, we can add more
statistics to collect.
**Context:**
_This is just to give a rough idea; I would need to write a lot more
than a few paragraphs in order to fully explain all the context here_.
End-to-end encrypted messengers are generally susceptible to MitM
attacks. In order to mitigate against this, messengers offer some way of
verifying the chat partner's public key. However, numerous studies found
that most popular messengers implement this public-key-verification in a
way that is not understood by users, and therefore ineffective - [a 2021
"State of Knowledge" paper
concludes:](https://dl.acm.org/doi/pdf/10.1145/3558482.3581773)
> Based on our evaluation, we have determined that all current E2EE
apps, particularly when operating in opportunistic E2EE mode, are
incapable of repelling active man-in-the-middle (MitM) attacks. In
addition, we find that none of the current E2EE apps provide better and
more usable [public key verification] ceremonies, resulting in insecure
E2EE communications against active MitM attacks.
This is why Delta Chat tries to go a different route: When the user
scans a QR code (regardless of whether the QR code creates a 1:1 chat,
invites to a group, or subscribes to a broadcast channel), a
public-key-verification is performed in the background, without the user
even having to know about this.
The statistics collected here are supposed to tell us whether Delta Chat
succeeds to nudge the users into using QR codes in a way that is secure
against MitM attacks.
**Plan for statistics-sending:**
- [x] Get this PR reviewed and merged (but don't make it available in
the UI yet; if Android wants to make a release in the meantime, I will
create a PR that removes the option there)
- [x] Set the interval to 1 week again (right now, it's 1 minute for
testing)
- [ ] Write something for people who are interested in what exactly we
count, and link to it (see `TODO[blog post]` in the code)
- [ ] Prepare a short survey for participants
- [ ] Fine-tune the texts at
https://github.com/deltachat/deltachat-android/pull/3794, and get it
reviewed and merged
- [ ] After the next release, ask people to enable the
statistics-sending
Create unprotected group in test_create_protected_grp_multidev
The test is renamed accordingly.
SystemMessage::ChatE2ee is added in encrypted groups
regardless of whether they are protected or not.
Previously new encrypted unprotected groups
had no message saying that messages are end-to-end encrypted
at all.
This mechanism replaces `Chat-Verified` header.
New parameter `_verified=1` in `Autocrypt-Gossip`
header marks that the sender has the gossiped key
verified.
Using `_verified=1` instead of `_verified`
because it is less likely to cause troubles
with existing Autocrypt header parsers.
This is also how https://www.rfc-editor.org/rfc/rfc2045
defines parameter syntax.
Any control information from the message
should only be downloaded when the message
is fully downloaded to avoid processing it twice.
Besides, "partial" messages may actually be full messages
with an error that are only processed as partial
to add a message bubble allowing to download the message later.
Old Delta Chat clients don't provide timestamps for added and removed members in messages, so at
least implicit member changes may be ignored as it's not clear if they are newer than explicit
member changes from modern clients. Lost messages aren't so frequent anyway, and overall
compatibility with old versions may be limited already.
Ignoring `receive_imf_inner()` errors, i.e. silently skipping messages on failures, leads to bugs
never fixed. As for temporary I/O errors, ignoring them leads to lost messages, in this case it's
better to bubble up the error and get the IMAP loop stuck. However if there's some logic error, it's
better to show it to the user so that it's more likely reported, and continue receiving messages. To
distinguish these cases, on error, try adding the message as partially downloaded with the error set
to `msgs.error`, this way the user also can retry downloading the message to finally see it if the
problem is fixed.
- sync declined calls from callee to caller, as usual in all larger
messengers
- introduce the call states "Missed call", "Declined call" and
"Cancelled all" ("Ended call" is gone)
- allow calling end_call()/accept_call() for already ended/accepted
calls, in practise, handling all cornercases is tricky in UI - and the
state needs anyways to be tracked.
- track and show the call duration
the duration calculation depends on local time, but it is displayed only
coarse and is not needed for any state. this can be improved as needed,
timestamps of the corresponding messages are probably better at some
point. or ending device sends its view of the time around. but for the
first throw, it seems good enough
if we finally want that set of states, it can be exposed to a json-info
in a subsequent call, so that the UI can render it more nicely. fallback
strings as follows will stay for now to make adaption in other UI easy,
and for debugging:
<img width="320" alt="IMG_0154"
src="https://github.com/user-attachments/assets/09a89bfb-66f4-4184-b05c-e8040b96cf44"
/>
successor of https://github.com/chatmail/core/pull/6650
this PR uses the initial "call messages" (that has a separate viewtype
since #7174) to show all call status.
this is what most other messengers are doing as well. additional "info
messages" after a call are no longer needed.
on the wire, as we cannot pickpack on visible info messages, we use
hidden messages, similar to eg. webxdc status updates.
in future PR, it is planned to allow getting call state as a json, so
that UI can render nicely. it is then decided if we want to translate
the strings in the core.
<img width="320" alt="IMG_0150"
src="https://github.com/user-attachments/assets/41ee3fa3-8be4-42c3-8dd9-d20f49881650"
/>
successor of https://github.com/chatmail/core/pull/6650
a dedicated viewtype allows the UI to show a more advanced UI, but even
when using the defaults,
it has the advantage that incoming/outgoing and the date are directly
visible.
successor of https://github.com/chatmail/core/pull/6650
Also verify not yet verified contacts w/o setting a verifier for them (in the db it's stored as
`verifier_id=id` though) because we don't know who verified them for another device.
We haven't dropped verified groups yet, so we need to do smth with messages that can't be verified
yet which often occurs because of messages reordering, particularly in large groups. Apart from the
reported case #7059, i had other direct reports that sometimes messages can't be verified for
various reasons, but when the reason is already fixed, it should be possible to re-download failed
messages and see them.
Also remove the code replacing the message text with a verification error from
`apply_group_changes()` as `add_parts()` already does this.
Encrypted message may create unencrypted groups
if the message does not have a Chat-Group-ID.
This can happen if v1 client sends an encrypted
message to opportunistically encrypted ad hoc group.
In this case `from_id` corresponds to the key-contact,
but we should add address-contact of the sender
to the member list.
We don't want to prefer returning verified contacts because e.g. if a bot was reinstalled and its
key changed, it may not be verified, and we don't want to bring the user to the old chat if they
click on the bot email address. But trying to return accepted contacts increases security and
doesn't break the described scenario.
- It's obvious that addresses are needed to add contacts, so `_by_address_list` looks excessive.
- The function only looks up `SELF` by address.
- The name was confusing because there's also `lookup_key_contacts_by_address_list()` that actually
looks up key contacts by addresses (not only `SELF`).
This PR adds a test to reproduce a bug raised by @adbenitez that peer
channels break when the resend feature is used.
---------
Co-authored-by: iequidoo <dgreshilov@gmail.com>
This should fix https://github.com/chatmail/core/issues/7030; @r10s if
you could test whether it fixes your problem
The crash happened if you received a message that has the from contact
also in the "To: " and "Chat-Group-Member-Fpr: " headers. Not sure how
it happened that such a message was created.
