Hi,

 

just to mention this. If you use the stored password hash, it equals to using a plain text string. Depending on your threat model it might or not be an issue that admins have access to the password used to encrypt mails.

 

Aki

On 04/03/2023 16:12 EET Jeremy <mailinglist-subscriptions@protonmail.com> wrote:

 

 

Hi again,

 

I was able to solve both questions. I was overthinking things.

 

A solution to the first question about mail_attribute_dict was simply to use other available variables to point to the virtual user's maildir paths. Like so: /var/mail/%d/%u/dovecot-attributes

 

As for the second question:

When I asked it, I was uncertain if dovecot would be able to cope with a hashed password for userdb_mail_crypt_private_password. I somehow believed dovecot required a plain text password there, as per the '%w' in the example password_query. Turns out this was not the case. Simply providing the already hashed password of the password field did the trick. So:

 

password_query = SELECT \

email as user, password, \

password AS userdb_mail_crypt_private_password \

FROM virtual_users WHERE email='%u';

 

Hope this is of help to others if they stumble upon this question.

 

------- Original Message -------

On Thursday, February 23rd, 2023 at 08:53, Jeremy <mailinglist-subscriptions@protonmail.com> wrote:

 

Hi again,

 

I am using dovecot 2.3.16, along with postfix and a PostgreSQL database for managing virtual accounts.

 

After an initial topic from me about encrypting already existent mail, I could now use some pointers on how to set up the mail-crypt plugin for pure virtual accounts (i.e. that have no matching system users and/or home directories. I hope somebody can clarify a few things that are not entirely clear to me yet.

 

After doing my own research, I believe the following should be possible:

 

I'd like to use the password of virtual email accounts to let dovecot encrypt/decrypt the keys needed to encrypt/decrypt the mail in the relevant folders.

 

As per the documentation @ https://doc.dovecot.org/configuration_manual/mail_crypt_plugin/ I believe this would be all the configuration I need:

 

# Config

mail_attribute_dict = file:%h/Maildir/dovecot-attributes

mail_plugins = $mail_plugins mail_crypt

 

plugin {

mail_crypt_curve = secp521r1 # or some other preferred curve

mail_crypt_save_version = 2

mail_crypt_require_encrypted_user_key = yes # necessary for encrypting keys with user password

}

 

# File: /etc/dovecot/dovecot-sql.conf.ext

password_query = SELECT \

email as user, password, \

'%w' AS userdb_mail_crypt_private_password \

FROM virtual_users WHERE email='%u';

 

My first question is:

Is it possible to configure mail_attribute_dict in such a way as to not use home directories. Since I only use virtual accounts, without those accounts having home directories, can I somehow tell dovecot to save the attributes into the PostsreSQL database, for instance? If not, can you suggest another approach, without having to create home directories for virtual users?

 

My second question is:

The documentation warns about not using password directly in the above SQL query:

 

Choosing encryption key

DO NOT use password directly. It can contain % which is interpreted as > variable expansion and can cause errors.

 

Does this refer to not accidentally substituting '%w' with password? In other words, if I leave the above query as is, should I be good, even if plain text passwords of users potentially have % signs in them? Or would I need to take further measurements? (The passwords in my database are already hashed, by the way).

 

I hope somebody can offer some guidance on this. Thanks.

 

---
Aki Tuomi