Mention usage of Message Authentication Codes

[NotAFile]

I believe that it is somewhat irresponsible to not mention Message Authentication. Otherwise, users will copy the insecure code in the README without realizing e.g. CBC without a MAC is trivially broken.

[ricmoo]

You are welcome to update the documentation and submit a pull request, but please keep in mind this library is for a cryptographic primitive, so it’s scope is intentionally limited.

There are many ways to use AES in general, and not all uses of CBC require (or can even support) a MAC, but an outline (and links to Wikipedia) of how and when to use a MAC would be wonderful.

Thanks! :)

[cristianocca]

Might want to also mention that AES CTR is malleable (ciphertext can be easily modified and remain unnoticed if no authentication is done as mentioned above) and also if encrypted data belongs to a small domain of possible values, those values can be guessed if the same counter initialization value is reused for every encryption.