Re: Mail-crypt plugin clarification
> On December 15, 2017 at 2:29 AM Joseph Tamwrote: > > > Aki Tuomi writes: > > > Dovecot does support making it difficult to prevent access to the stored > > mail. > > Those who have had problems understanding the documentation might find > this unintended double-negative ironically funny. > Indeed. Although we are open to improvements for the documentation, or even pointing out where it's wrong. > > You can, with suitable workflows, ensure that the user's emails are not > > readable by anyone but the user. Of course the only way to be fully > > sure is to use end-to-end encryption, ... > > "Ensure" (or OP: "impossible") are very high standards of privacy. > If the OP really means it, then since a third party has control over > the (virtual or real) hardware, the server should never have access to > private keys or decrypted data. (We're in agreement I think.) > You are quite right. The mail-crypt plugin cannot provide absolute guarantees that the data won't be accessible by sufficiently determined adversary, due to the fact that the keys are indeed on the server, or accessible by the server. > If the OP lowers their standards to "inconvenient" to gain access, > then the plugin is enough. It will keep the honest admin honest. > > > ... like PGP or S/MIME, but this does go a long way to prevent admin access > > to user's email. > > Don't ignore metadata; who/when/where (and headers?) could reveal much > information. > > Joseph Tam It's always all about who you are guarding against. I'd say that against your hosting provide, mail crypt can provide reasonable safeguards, especially if the storage is not on the same device. The weak point is, as you point out, key management and handling, and special attention should be paid to this and I suggest clearly outlining the threats you are planning on mitigating and how the solution(s) you use achieve this. Aki
Re: Mail-crypt plugin clarification
Aki Tuomi writes: Dovecot does support making it difficult to prevent access to the stored mail. Those who have had problems understanding the documentation might find this unintended double-negative ironically funny. You can, with suitable workflows, ensure that the user's emails are not readable by anyone but the user. Of course the only way to be fully sure is to use end-to-end encryption, ... "Ensure" (or OP: "impossible") are very high standards of privacy. If the OP really means it, then since a third party has control over the (virtual or real) hardware, the server should never have access to private keys or decrypted data. (We're in agreement I think.) If the OP lowers their standards to "inconvenient" to gain access, then the plugin is enough. It will keep the honest admin honest. ... like PGP or S/MIME, but this does go a long way to prevent admin access to user's email. Don't ignore metadata; who/when/where (and headers?) could reveal much information. Joseph Tam
Re: Mail-crypt plugin clarification
On 14.12.2017 01:07, Joseph Tam wrote: > rje writes: > >> I'm looking into ways to encrypt the stored email on my server. The >> idea is >> to make it impossible for my hosting provider (who has access to my >> VPS) to >> read the mail from the disk. > > Just to be clear, if at any point your VPS has access to the plaintext > mail (or keys that decrypt mail), then the VPS provider could access > your decrypted mail. > > To make it unfeasible for your VPS to read your mail, it has to arrive > at your VPS pre-encrypted. I can envision a system where you import > encrypted mail into your mail store, then use client IMAP access to > be decrypted locally by your mail reader. However, metadata is still > accessible by your VPS provider. > > If your VPS is the MTA that directly handles SMTP from your correspondees > sending you unencrypted messages, you can't lock out a sufficiently > skilled platform admin. > > Joseph TamHi! Dovecot does support making it difficult to prevent access to the stored mail. You can, with suitable workflows, ensure that the user's emails are not readable by anyone but the user. This can be done by encrypting the user's private key using user's password (or it's derivate, such as sha256 sum of it). Of course the only way to be fully sure is to use end-to-end encryption, like PGP or S/MIME, but this does go a long way to prevent admin access to user's email. Downside of course is that if the user ever forgets his password, then those emails are lost as well. We have plans to add DR support for this, but it's still WIP. Aki
Re: Mail-crypt plugin clarification
rje writes: I'm looking into ways to encrypt the stored email on my server. The idea is to make it impossible for my hosting provider (who has access to my VPS) to read the mail from the disk. Just to be clear, if at any point your VPS has access to the plaintext mail (or keys that decrypt mail), then the VPS provider could access your decrypted mail. To make it unfeasible for your VPS to read your mail, it has to arrive at your VPS pre-encrypted. I can envision a system where you import encrypted mail into your mail store, then use client IMAP access to be decrypted locally by your mail reader. However, metadata is still accessible by your VPS provider. If your VPS is the MTA that directly handles SMTP from your correspondees sending you unencrypted messages, you can't lock out a sufficiently skilled platform admin. Joseph Tam
Mail-crypt plugin clarification
I'm looking into ways to encrypt the stored email on my server. The idea is to make it impossible for my hosting provider (who has access to my VPS) to read the mail from the disk. So I'm looking into ways to do this, and I found the mail-crypt plugin for dovecot. Unfortunately I find the documentation very hard to understand. There is no clear description of what the goal and purpose of the plugin is, or how it works. Most of the documentation is very short and provides no explanation. So here are some questions - I will gladly help to update the documentation when some of these questions are answered :) If you cannot answer them all, please tell me what you know.. - It seems mail-cypt will transparently encrypt/decrypt mail - so it stores it on the server in encrypted form, but dovecot serves it unencrypted over IMAP. Is this correct? - It seems that mail-crypt needs both a private and a public key to work. Is this correct? - If mail-crypt has both private and public key in its configuration, does that not defeat the purpose of the whole thing? Anyone with access to the disk will be able to read everything? Regarding the settings: mail_crypt_global_private_key(_n) - Private key to decrypt files, you can specify many mail_crypt_global_public_key - Public key to use to encrypt files, you can specify one - How does this work? What does mail-crypt do when multiple private keys are specified? mail_crypt_private_key - Private key to decrypt user's master key, can be base64 encoded mail_crypt_private_password - Password to decrypt user's master key or environment private key - What is the relation between a users master key, and the private/public global keys above? What is an environment private key? TIA, and as I said above, I will help with updating the docs! -- Sent from: http://dovecot.2317879.n4.nabble.com/