[OT] Where can I find some papers to read on mail (and envelope) security?

[Philipp Klaus Krause]

There has been plenty of research on email security and the need for
encryption is well-known.

However, I wonder if there has been any research on mail security. Of
course, one could just put a GPG-encrypted letter in an ordinary
envelope, but there are more common measures that are meant to give some
additional security over the standard mail. I wonder how well those work.

Are there any good textbooks, etc?

There are a few aspects I can think of (but there is probably more):
* Patterns printed on the inside of envelopers. These are meant gainst
the use of light to read the contents of an unopened enveloper. How
strong are these in the face of image recognition? Did someone study
such patters?
* Tamper-proof enevelopes, meant to make it hard to open an envelope
unnoticed. How well do these work? Does it even make snsne to put much
effort into them, as an attacker could use a new envelope (though there
might be some difficulties involved to get or fake the right postmark)?
* There seems to be some literature on the security of wax seals (e.g.
"Licet ad regimen", published in 1198 - does anyone know of a German,
French or English translation).

Philipp