[horde] Horde as a Secure Document Delivery mechanism

[Kevin Myer]

For a variety of reasons, many organizations opt for some sort of Secure
Document Delivery mechanism.  In many cases, encrypted email (proprietary or
open) is used.  However, this requires both sender and receiver to agree on and
use the same encryption mechanism for exchanging email.  Where that is not
feasible or practical, a SSL-secured website is used as an intermediary.  The
recipient is sent a link to a document on the website and can securely download
it.

My thinking is that IMP, using Linked Attachments, can function the same way. 
In evaluating the security of such a setup however, the following comment in
imp/attachment.php creates a problem:

// This does *not* include IMP's base.php because we do not need to be
// authenticated to get the file. Most users won't send linked
// attachments just to other IMP users.

Since the email with the link is potentially not encrypted, a malicious third
party would simple need to observe or obtain the link to obtain the "secure"
document.

So my question would be, what would be needed, either within the Horde
Framework, or IMP, or both, to add something like a secure attachment checkbox.
 If checked, the document would require a username and password (which could
potentially be provided out of band to the third party).  What would it take to
have linked attachments treated as an object, to which Horde Permissions could
be assigned?  I somehow see a mix of Gollem, Horde, and IMP coming together
here - where a user could use Gollem to view their linked
attachments/documents, and could use IMP to send messages with links to those
attachments.  SSL would secure the transport, Gollem could be used to control
actual file permissions, and Horde provides the framework...

Thoughts,
Kevin

-- 
Kevin M. Myer
Senior Systems Administrator
Lancaster-Lebanon Intermediate Unit 13  http://www.iu13.org