Encryption

Encryption transforms readable data into scrambled noise using a key; the right key reverses it. The lock icon in your browser means every byte between you and the site travels encrypted — anyone listening on the wire hears only static.

Modern encryption doesn't rely on hiding the method — the algorithms are public and studied by everyone. Security comes from the key alone: math so lopsided that scrambling is instant but unscrambling without the key would take longer than the age of the universe.