Bob and Alice

Alice wants to send Bob a secret…
How can she avoid exchanging keys with Bob while at the same time avoid an eavesdropping Eve?

 

 

Alice places the secret inside a box.

 

 

She places a padlock and sends it to Bob.

 

 

Bob adds his own padlock and sends it back to Alice.

 

 

Alice removes her padlock and sends it back to Bob.

 

 

Bob opens his padlock and removes the secret.

Mission accomplished: the secret changed hands while no keys were exchanged.

Inspired by a passage on encryption on Simon Singh’s The Code Book.

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