AES-256-GCM Authentication Tag Does Not Cover First Ciphertext Blocks When AAD Is Empty

Missing cryptographic step in Caliptra Core Firmware (aes_256_gcm_update module) results in an incorrect GCM authentication tag. When the streaming AES-256-GCM API is used with empty AAD, the hardware GHASH accumulator state is not saved after the first update call, causing the final tag to exclude the first batch of processed ciphertext. Ciphertext produced by that call may be modified without the tag reflecting the change.

This issue affects Core Runtime Firmware: from 2.0.0 through 2.0.1, 2.1.0.