SPRUJB6B November 2024 – May 2025 AM2612
Figure 7-108 GCM
OperationFigure 7-108 illustrates one round of a GCM operation for both encryption and decryption. A 32-bit counter is used as IV (as it is for CTR mode). The data is encrypted the same way as CTR mode, by XOR-ing the crypto core output with the input. After the encryption/decryption the ciphertext is XOR-ed with the intermediate authentication result. The XOR-ed result is used as input for the polynomial multiplication to create the next (intermediate) authentication result. Refer to paragraph 1.6.2 for details about the GCM protocol.