how to decrypt AEAD_AES_256_GCM?

Question

mc 5,406

I know there is AesGcm can decrypt 128 bit?

but what about 256 bit?

in 128 bit the tag is 16bit what about 256bit? tag size can not be 32.

Hui Liu-MSFT 48,676 Reputation points Microsoft External Staff

2023-06-12T07:25:04.3733333+00:00

Hi,@mc . Welcome Microsoft Q&A.

GCM has a limited key size of 128 bits. The AesGcm class supports creating or processing 96, 104, 112, 120, and 128-bit (12, 13, 14, 15, and 16-byte) tags. Unfortunately, a tag size of 256 bits (32 bytes) is not directly supported by the standard AES-GCM implementation in .NET.
mc 5,406 Reputation points

2023-06-12T11:55:56.1933333+00:00

give me an answer
Hui Liu-MSFT 48,676 Reputation points Microsoft External Staff

2023-06-22T07:43:40.8366667+00:00

Hi,@mc . As Bruce said, you could google according to your needs and use the appropriate library. I can't make a recommendation due to policy.

1 answer

Hui Liu-MSFT 48,676 Reputation points Microsoft External Staff

2023-06-12T07:25:04.3733333+00:00

Hi,@mc . Welcome Microsoft Q&A.

GCM has a limited key size of 128 bits. The AesGcm class supports creating or processing 96, 104, 112, 120, and 128-bit (12, 13, 14, 15, and 16-byte) tags. Unfortunately, a tag size of 256 bits (32 bytes) is not directly supported by the standard AES-GCM implementation in .NET.
mc 5,406 Reputation points

2023-06-12T11:55:56.1933333+00:00

give me an answer
Hui Liu-MSFT 48,676 Reputation points Microsoft External Staff

2023-06-22T07:43:40.8366667+00:00

Hi,@mc . As Bruce said, you could google according to your needs and use the appropriate library. I can't make a recommendation due to policy.

Answer 1

Bruce (SqlWork.com) 77,631 Volunteer Moderator

You will need an alternate encryption library. Google nuget aes 256, and pick the package that best fits your needs.