(Continuing the '
real-world' application of this)
Assuming
Eve only wants to steal '
useful' items, or assuming you can
generate an
infinite number of
padlocks (which you can on a
computer), you could just let
Bob send
Alice his
unlocked padlock, then
Alice locks the
medicine in the
chest. Of course, this has the slight problem, where Alice could
swap the
padlock for one of her own.
In the real world, that basically means, you can give everyone a copy of your
RSA public key (padlock), because it's only useful for
encrypting (locking) things, you need the
private key (the key) to
decrypt (unlock) it --
however you need to be sure you have the
correct padlock, lest you be tricked into encrypting something to some
evil third party.