Irreversible Origami Envelope

Question

In Patrick Rothfuss' novel The Wise Man's Fear, the main character briefly mentions that he has a way of folding a letter to be its own envelope in such a way that it is not possible to reopen the envelope/letter without tearing it, giving a method of secure communication without sealing wax or similar. Does such a folding method actually exist?

I've done some experimenting myself, and some searching online, but the closest I've found are envelope designs that don't need tape/glue to stay closed. Nothing I've found has the key property of being impossible (or at least very difficult) to unfold again without tearing.

Answer 1

While not impossible to open without tearing, and requiring cuts as well as folds (which disqualifies the method as origami to an origami purist), there is a form of letterlocking that involves cutting a thin strip from the blank margin of the letter, folding the letter, and then punching holes through the letter with an awl, and threading the strip through the holes in an interlocking knot-like pattern, which would make it very difficult to open the letter without tearing the thin delicate strip of paper.

See: https://vimeo.com/189348055

http://letterlocking.org/categories states that this blank margin method of letterlocking was "used by Queen Elizabeth I of England, Mary Queen of Scots, Catherine DeMedici, and many others."

Answer 2

So I may have stumbled onto a lead while doing some unrelated folding. This method isn't impossible to unfold without tearing, but it requires a fair bit of force (or an understanding of how it was folded) to do. Also, as far as I've been able to test, it's not possible to fold the letter back up in the same way once it's been unfolded, so if you've agreed on this method ahead of time with the recipient it serves a similar anti-tamper purpose as a wax seal, perhaps somewhat less secure but requiring no wax. Finally, it's very fast and simple to do. Here's the method:

1. Start with your letter
2. Fold it into roughly 3rds. It's not important that it be exactly 3rds but it is important that it's square, i.e. that the two folds are parallel with each other and perpendicular to the base, or as close as possible
3. Pinch one end of the paper to open up a "tunnel" at that end
4. Push the other end of the paper into the tunnel. Don't crease any of the folds yet!
5. This is the tricky part: push the free end of the paper as far into the tunnel as possible. This gets increasingly difficult the further you go due to the friction. I've found the it works best with more sturdy papers (printer paper does a fair job), and sturdier paper is harder to unlock. With the flimsy notebook page I used for this demonstration, I got the paper less than a 3rd of the way in
6. Now find the place where the paper ends inside the tunnel. Move up a little bit so you have a centimeter or so on both sides of where you're about to cease, and crease hard. This is the locking fold. Essentially you're forming this shape, but with the free end tucked inside the letter:
7. Crease the other side so your paper lays flat and you're done!

Like I said, this isn't perfect. You can definitely unfold the letter without tearing it, but I think this general idea (hidden folds inside the paper structure that are creased after tucking) has promise. I'll be playing around with this idea some more, and I'll update you all if I find a more secure method.