This is just a quick teaser on how Public Key Cryptography works … Here we go, you’ll need to look at the picture above as I describe the functions.
The notion of PKI is that there is a pair of Keys, one a private key, and one a public key (we will cover how they’re generated in another teaser). On the image you see the private key in black, and the public key in red. One private key can generate many public keys.  The beauty of the key pair, is that while anyone can use the public key to encrypt (munge up) data so it cannot be read by anyone, to make it secret, only the holder of the private key can unlock the secret to get the data back. So if I want someone to send me some secret that I don’t want anyone else to know, I send them my public key and only I can decrypt it, or open it up.
Let’s walk through a common procedure which is used to verify one person to another. In our picture the man in black wants to establish a secure communication channel with the woman in blue. So John, the man, calls Sue and they send each other their public keys to start.
Using a land line, John calls Sue and they choose 9 words that they’ll send to each other encrypted with their respective private keys. Once they each receive the corresponding words encrypted with their public key, only John and Sue can use their respective private keys to read the list of words the other sent. This now proves to them that their communications can be exchanged privately and securely. And they have just completed a simple process of authentication.  Meaning they have proven one to the other that they were the sender of the message.
Of course this is a super simplified version of the process and there are many more complex things that can be done, like they could send each other encrypted copies of their passports and diver’s licenses, and they could add a third party to verify each of them independently and certify who they are if they needed further assurances that they are communicating with the intended person, but this gives you the idea of how this works.
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