Figure 2: Asymmetric or Public Key Encryption

In this figure, a sender -- let's say Sue -- is using your public key to produce a ciphertext for you. But the process also works backwards; you could encrypt a plaintext with your private key and send the resulting ciphertext to Sue. Decrypting the ciphertext with your public key proves that the ciphertext had to come from you. This provides authenticity, without privacy. Your public key is public, so anyone could decrypt this ciphertext, not just Sue. But public/private key pairs make digital signatures possible, which provide authentication and integrity without sacrificing privacy.

1. You give Sue (aka Sender) a copy of your public key.
   
   
2. Sue uses your public key to encrypt the plaintext to produce a ciphertext for you.
   
   
3. She then gives (just) the ciphertext to you, and
   
   
4. You use your private key to decrypt the ciphertext to reproduce the plaintext.