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Let's say I send you an email, encrypted using your public key. I know who you are, because only you can decrypt that message. But how do you know who I am?

The magic of public-private keys is that they work both ways. When we encrypt messages, we use a public key to encrypt it, then a private key to decrypt it. "Signing" a message is doing the reverse. You're creating an encrypted signature using your private key, which can then be decrypted using the public key. This way, anyone can use your public key to verify that it was sent by someone with your private key (which is hopefully you).

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