Wrapping keys and best practices for encrypting large documents

In the previous section, we learned how symmetric keys are often derived from passphrases. Encrypting data with a passphrase or passcode that the user memorizes (or stores in a password wallet) is at the core of many, many solutions that leverage cryptography, such as to encrypt documents or files. The next time you unlock your laptop with a passphrase or your phone with a PIN, think about the key derivation functions and ciphers that are being executed!

By reading this chapter up to this point, you should already be able to build an application like the one we just described with Node.js. For example, you could use Argon2 to derive a key from a passphrase submitted by the user, and then use AES-GCM to encrypt and decrypt files.

However, passphrases are not static. That is to say that users do change their passphrases, sometimes because they want to rotate them, or sometimes because their previous one was compromised...