> Also, in the US, the police can request a "mail cover" > (which means recording who all your snail mail is from) > with much less legal formality than a search warrant, > and if they get a warrant to open all your incoming mail, > I don't think they're required to notify you.
Is there a way to RELIABLY find the mail was opened? Reason: If the mail sent is eg. a CD with a set of OTP keys, then the adversary gains next to nothing by intercepting it IF the interception is detected (the keys just get discarded and new set is sent to another address). Then it could be possible to securely send large volumes of confidential data by mail; you prepare the pairs of CDs - one with cryptographically random data, one with the real data XORed by the first set. You send the first set. If it arrives unopened (which can be communicated safely even over an unsecured channel), you send the second set; if it arrives opened, you generate the CD pairs again and send the new first set. If the adversary intercepts only one half of the transported data, they gain nothing more than the fact some amount of data was sent. (Of course, hand-to-hand exchange is more secure, but it is suitable for operative handling of keys in urban setting, not when an overseas flight would come to question.) One of my ideas was to put a small piece of film or photographic paper, detect that it was exposed to light, but then the adversary can put in a new piece of the light-sensitive material and reseal the package. The same problem goes with the various kinds of seals. Comments, hints, keywords to look up?
