Modern cryptosystems rely on “keys” as the secret way of coding or decoding information on which trust is built. “Symmetric encryption” relies on sharing the same key with other trusted parties. I encrypt data with the same key that you use to decrypt it. It is like us both sharing the same key for a bank lockbox.
But what if we have never met each other? How will we exchange these secret keys securely? “Asymmetric cryptography” solves this problem. The idea is to separate a secret key into a public key, which is shared with everyone, and a private key that remains secret. The two keys are generated such that something that is encrypted with a public key is decrypted with the corresponding private key, and vice versa. This figure illustrates how public cryptology works to protect both the confidentiality and the integrity of a message.
From P.W. Singer and Allan Friedman’s Cybersecurity and Cyberwar: What Everyone Needs to Know.
Image credit: P.W. Singer, Allan Friedman, and Jordan Clayton. Used with permission.