For the AES-GCM mode within many cryptomodules, their FIPS-validation certificates list the options:
- Payload Length: 504, 512, 1016, 1024
- AAD Length: 0, 504, 512, 1016, 1024
For example in OpenSSL, "int aad_len" is the term for the 'AAD Length'.
What do these numbers refer to?
Are these maximum allowed, minimum allowed, or the exact length required for the payload (cyphertext) and additional authenticated data (AAD) (plaintext)? Do they refer to AES-GCM input or output? Is there a default (like with a 96-bit IV)?
As a newbie developer using AES-GCM what should I be concerned with picking / using these values? Does anyone have online references to these?