What is encryption, in plain terms?

Encryption turns readable data into scrambled data that only someone with the right key can turn back. The method, called the algorithm, is public; the secret is the key. Good encryption means that without the key, even a powerful computer cannot recover the data in any useful time. You use it every day: HTTPS on websites, the VPN to the office, messaging apps, disk encryption on laptops and phones, and backups. It protects data in transit against anyone who can listen on the network, and data at rest against anyone who steals the disk. It does not protect data from someone who already has the key, or who controls a device where the data is decrypted, such as malware on a logged-in laptop. That is why encryption sits alongside access control, patching and monitoring rather than replacing them. A network sensor sees that encrypted connections happen, with their metadata, but not their content.

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