Q:

Kruskal's hard to refold envelope

In Wikipedia's bibliography of Martin Kruskal it is said:

Martin, who had a great love of games, puzzles, and word play of all
  kinds, also invented several quite unusual origami models including an
  envelope for sending secret messages (anyone who unfolded the envelope
  to read the message would have great difficulty refolding it to
  conceal the deed).

Unfortunately, this is the only information in Wikipedia about Kruskal's secret message envelope.
Does anyone know the history of this envelope, or where I can find more information about it?
This envelope seems like a puzzle, since there may have been a clever trick to refold it.

A:

It is really hard to find something on the Web about Martin Kruskal in relation to origami.
There is a link missing in Wikipedia, so maybe this information is just gossip.
If you want to see how to fold an envelope for sending secret messages, you can check out:

This method for a hard-to-open envelope.
This method and this method for kind-of-hard-to-fold-back envelopes.

