var gcm = new AesGcm(Encoding.UTF8.GetBytes("APIV3密钥")); byte[] cipherTextBytes = Convert.FromBase64String("平台证书ciphertext字段"); byte[] nonce = Encoding.UTF8.GetBytes("平台证书nonce字段"); byte[] ciphertext = cipherTextBytes.Take(cipherTextBytes.Length - 16).ToArray(); byte[] plaintext = new byte[ciphertext.Length]; byte[] tag = cipherTextBytes.Skip(ciphertext.Length).Take(16).ToArray(); byte[] associatedData = Encoding.UTF8.GetBytes("平台证书associated_data字段"); gcm.Decrypt(nonce, ciphertext, tag, plaintext, associatedData); string text = Encoding.UTF8.GetString(plaintext);