Message encryption at rest

[or-else]

Encrypt messages stored in the database. The intent is to prevent access to message content using database tools.

This is not end-to-end encryption.

[ercsnmrs]

@or-else do you have any acceptance criteria in mind? i can take a look on this one, i am also thinking if the implementation is backwards compatible?

[or-else]

Here is some rough outline. Feel free to make suggestions or corrections:

1. Make it optional: it should continue to work with no encryption if user desires so.
2. Use standard symmetric encryption from https://pkg.go.dev/crypto, for example AES.
3. Allow key to be specified either in tinode.conf or from the command line
4. Encrypt only the content: field of the message

   chat/server/datamodel.go

   Line 608 in 8702626

   Content any `json:"content"`

5. Think how to convert existing installations from un-encrypted to encrypted and maybe back (should there be a separate tool? or maybe use tinode-db?)
6. Attachments: should they be encrypted too? They probably should but that can be done later.
7. I think the best place to encrypt is here:

   chat/server/store/store.go

   Line 667 in 8702626
   to decrypt here

   chat/server/store/store.go

   Line 749 in 8702626

   return adp.MessageGetAll(topic, forUser, opt)

Did I forget anything?

[ercsnmrs]

@or-else gotcha, sounds great, i can work with that.