We support GCM mode including both encryption and decryption parts in this implementation.
Attention
The bit-width of the interfaces we provide is shown as follows:
| payload | lenPld | AAD | lenAAD | IV | cipherkey | cipher | lenCph | tag | |
| GCM-AES128 | 128 | 64 | 128 | 64 | 96 | 128 | 128 | 64 | 128 |
| GCM-AES192 | 128 | 64 | 128 | 64 | 96 | 192 | 128 | 64 | 128 |
| GCM-AES256 | 128 | 64 | 128 | 64 | 96 | 256 | 128 | 64 | 128 |
Caution
Applicable conditions:
1. The bit-width of initialization vector must be precisely 96 as recommended in the standard to promote interoperablility, efficiency, and simplicity of the design.
2. We provide the MAC value instead of a FAIL flag in decryption part, therefore, you should take care the MAC which is given by the encryption part to judge the authenticity of the data. If the data is authentic, then the MACs should be equal.
The algorithm flow chart of encryption part of GCM mode is shown as follow:
As we can see from the chart, the GCM encryption part can be divided into two individual parts: The Counter Mode (CTR) and The Galois Message Authentication Code (GMAC). GCM is used to encrypt the plaintext to ciphertext, and GMAC is used to generate the MAC. The algorithm flow chart of decryption part of GCM mode is shown as follow:
The decryption part is very similar with the encryption part of GCM mode. The only difference is that we decrypt the ciphertext to plaintext in the decryption part.
The internal structure of both encryption and decryption parts of GCM are shown as the figures below: