Linux-Noob Forums

Full Version: Encrypting SMTP

Hi all,


I only have a basic understanding of what I have and what I want, so I hope I can provide enough info.


We have a Linux Server (Dell T610) running RHLE 4. For the most part, our software vendor requires this type of server for their software. They also provide some basic support & 90% of the time they are the ones who touch the server, because I nor anyone else in our building know anything more than some elementary Linux.


Anyway, they setup a SMTP mail server using one of my google accounts that basically just sends mail with an attachment. Pretty handy.


We're currently trying to get a module they offer that sends letters to our customers via email instead of snail mail (which is very expensive when you muliply the price of a stamp by 3k-4k each day). The problem is the attachment is just a plain text file. Obviously, this a major security issue since most of what we deal with contains confidential/personal (SSN, DOB's, etc.) info.


On to my point! We want those emails secured in some way & our vendor claims they cannot provide this feature. Is there something I can add to our server (or have the software vendor add probably haha) that will encrypt messages being sent from the SMTP mailer?


I would also settle for a similar service that is already provided by an online vendor such as Zixmail for example, however in-house would be first preference)




Short answer: no.


Reason: SMTP is a plain-text communication link that requires the envelope header to be read, meaning that the receiving server needs an established communication channel (swapping keys) first prior to the payload (the body) being sent.


However, there IS a half-way stage. Like HTTP, the actual URL is transmitted plain-text but the content is encrypted. What you're *really* after is to encrypt the attachment using something like PGP keys so that if the data was sniffed it wouldn't make any sense without the right keys. This *is* achievable, but will require some preprocessing during the construction of the email so that an already-encrypted attachment was dropped into the body of a plain-text email.


The only other method I could suggest is to mail customers a link which requires credentials over HTTPS to read it. It wouldn't matter too much if the email fell into the wrong hands, since the URL would require customer authentication before exposing confidential data. Benefits of this system are:

- tracking who does/doesn't visit the URL

- assurance that no confidential information is being transmitted

- safety if the email falls into the wrong hands

- maintaining confidential data behind an authentication mechanism


Drawbacks are:

- having to support the bandwidth of making the data web-readable

- additional overhead of managing user accounts (which may already be fundamental, irrespective of which method is chosen anyway)


Dunno if that helps, but I know what would be easier for me to use (as a customer).