Cryptography Headers in Cryptographic Libraries I have a question regarding the headings in cryptography. In python, in the pycryptodome module, I am doing symmetric encryption, which asks for a header that goes as follows:

Cipher = Crypto.Chiper.AES.new(key)
Cipher.update(HEADER)


My question is, how do I configure the header correctly? I've seen examples of just putting a str, like , and never explaining beyond what they are for, because I should use them, how I should use them, etc. If I need to know how to use them correctly, because I should use them, I understand that they are associated data that are linked or related to the content to be encrypted.
What associated data (or encrypted header in the plaintext message) to use is dependent on the protocol, not on the cryptographic algorithm.

Generally, for messages in a transport protocol, you'd use the to avoid replay attacks.

The header data may also contain other meta-data that you want to authenticate for the message.

Beyond that, there is nothing to tell you, because you've only listed a (partial) algorithm, and not the protocol.