The correct solution is to use a public-key-like scheme, where somehow first king get a lock from second king and seal the box with this lock and of course only second king has the key to open it.

So this is a way to narrate public key cryptography, as I was thinking about this I asked myself if there are any other situations in real our daily lives that we use a scheme like this and I found 2. Our email addresses are actually a form of our public keys, We distribute them freely (without fearing from spam:) and when a website wants to send a secret or verify our identity (if we really own the email address and Facebook really uses this to understand if you belong to a certain company and/or university) they use our public key but only we using our passwords (our private keys) can read(decrypt) the message (assuming no body reads our emails along the way... yeah definitely not :). One more scenario is our home addresses which are another form of public keys and in this case our private keys are in fact our metal keys to mailbox.

So can you think of any other scenarios that we use public key cryptography in our daily lives?

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