Best mail encryption solution for per-user

[tai74 at vfemail.net]

Quoting tai74 at vfemail.net:

> Aki really thanks for reply,, I hope for continue the conversation,
>
>>> Do you have advice about Dovecot plugins for mail encryption:
>>>
>>> https://wiki2.dovecot.org/Plugins/MailCrypt
>>> https://0xacab.org/riseuplabs/trees
>>>
>>> I like NaCL based encryption but the MailCrypt plugin is better
>>> because it's maintained by Dovecot developers (is this correct?)
>>>
>>> Hard to understand MailCrypt docs so may I ask, may I provide per user
>>> encryption? I don't like global because I want every user to have
>>> different encryption based on their password. But I don't see the
>>> useful of per-folder encryption. Docs for TREES are easier to
>>> understand it will work on a per-user encryption using the user
>>> password to decrypt the needed keys.
>>>
>>> How about indexing? Does native fast Dovecot indexing must be turned
>>> off for one of these or both? Is this a big performance hit? And how
>>> to turn off indexing on a per-user basis?
>>>
>> Mail crypt plugin in dovecot core is indeed developed and  
>> maintained by us. Turning on encryption is simple, but you'll have  
>> to consider key management closely.
>>
>> The simple instructions are
>>
>> mail_plugins = $mail_plugins mail_crypt
>> mail_attribute_dict = file:%h/Maildir/dovecot-attributes
>>
>> plugin {
>>  mail_crypt_curve = <some curve you like>
>>  mail_crypt_save_version = 2
>> }
>
> With no other settings, I understand this to auto-generate keys.
> It's putting them in mail_attribute_dict? How is that related to
> mail_crypt_private_key,, which is for what then?
>
>> This will turn on automatic key creation for folders and users.
>
> I guess it's saying "folders" mode because each folder has a keypair
> but I don't understand why a single keypair isn't enough? Because of
> possibility to have shared folders? Anywayz I'm confused how it relating
> against global mode and where user mode fits (there is no user mode
> say the docs).
>
>> NOTE that the keys won't be encrypted in this scenario.
>>
>> To encrypt keys you have few choices. You can use a static  
>> password, static ECC key, per-user password, per-user ECC key,  
>> per-user password protected ECC key.
>
> Sorry newb question, though how is this choice made (on different values
> of mail_crypt_require_encrypted_user_key?)
>
>> With the per-user model, the easiest, if you don't let users change  
>> password could be adding into userdb or passdb,  
>> mail_crypt_private_password = %{sha512:password}
>>
>> If you want users to be able to change passwords, you either need  
>> to manage the encryption passwords in user database, or call  
>> doveadm mailbox cryptokey password during password change.
>
> I have custom userdb lookup so I don't mind to manage key encryption
> passwords in database, but how do I do it? Is it by to include
> mail_crypt_private_password in the userdb lookup?
>
> Moreso,, if I want password same to be as regular IMAP password, is
> there security problem? I think it's possible to return plaintext
> password for userdb lookup with %w right?
>
> Moreso,, I don't see that to work because maybe pwd changes in userdb
> but encryption keys (stored where?) still be encrypted with old pwd
> no? In such case, what is to be done? Your indication was that doveadm
> can be used but that there is another soultion which doesn't become
> full evident to me yet.
>
> Is literally solution now I must also store keys in database and make
> custom pwd change module decrypt to re-encrypt them with new pwd?
>
>> Also we do not currently support DR keys, so if the per-user key is  
>> lost, you will not be able to recover the mails.
>
> Fair!
>
>> Forgot to add that currently it's not possible to encrypt indexes due
>> to how lib-index is designed.
>
> To infer your statement, this means indexing will work anyway ok even
> with encryption turning on? With caveat of have unencrypted metadata in
> index files? So that we must choose, unprotected metadata or remove
> indexing? May indexing be removed per-user, maybe from userdb lookup?

Adding questions: will encryption work equally with maildir, dbox, mdbox
et al?
Will encryption work with zlib compression?
I want to test encryption but only on a test account not all accounts,
possible to enable for just a coulple testing users?

Regards,Tai


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