The original comment is correct here. AES by itself is indeed just going to encrypt a single block of 128&#x2F;192&#x2F;256 bits. To encrypt a plaintext longer than that, you need to apply the cipher repeatedly on subsequent blocks. The exact mode in which that&#x27;s done is important.<p>For example in this case the code uses the CBC mode (a fact not mentioned anywhere in the document). CBC has the funny property that flipping bit X in cipherblock N will flip bit X in plaintext block N+1 (while completely scrambling plaintext block N). This is a very exploitable property. Which is why the standard advice would be that you always need to authenticate, not just encrypt. (E.g. encrypt-then-mac).<p>But of course this document doesn&#x27;t give even this most basic of crypto recommendations. Which endangers anyone who reads it and thinks they learned something.