According to spec, FOR GCM decrypt function input is IV, A, C, and T. As mentioned below:
5.2.2 Authenticated Decryption Function Given the selection of an approved block cipher, key, and an associated tag length, the inputs to the authenticated decryption function are values for IV, A, C, and T, as described in Sec. 5.2.1 above. The output is one of the following:
- the plaintext P that corresponds to the ciphertext C, or
- a special error code, denoted FAIL in this document.
I was referring a AES GCM reference model available online and I saw for decryption to calculate the PT result it does not consider Tag value.
Does the output (PT) depend on Tag value (T)?
Reference Model Link: https://github.com/mko-x/SharedAES-GCM/blob/master/Sources/gcmtest.c