No associated data (AAD)

[xayaank]

Currently passes:
AESGCM(key).encrypt(iv, data, None)

Meaning:
header is NOT authenticated
attacker can flip MAGIC/VERSION without breaking decryption logic early

BETTER (include header as AAD):

AESGCM(key).encrypt(iv, data, HEADER)

and:

AESGCM(key).decrypt(iv, ct_and_tag, HEADER)