How to implement AES GCM 256 bytes with Key & IV but without using the tag in C# 4.7.2 or any .net version

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How to implement AES GCM 256 bytes with Key & IV but without using the tag in C# 4.7.2 or any .net version

Sanket Joshi 20

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Answer 1

Anonymous

Hi @Sanket Joshi , Welcome to Microsoft Q&A,

Implementing AES-GCM without using an authentication tag ("tag") can introduce security vulnerabilities. The "tag" in AES-GCM is used as an integrity check to ensure that the ciphertext has not been tampered with in transit. Skipping or ignoring the tag means you lose this protection, making the encryption vulnerable to undetected tampering, which violates secure cryptographic practices.

Tag is an integral part of AES-GCM mode, which is one of the core design principles of AES-GCM. If you do not need integrity verification, you should choose other encryption modes, such as AES-CBC or AES-CTR, but you will need to handle authentication and integrity verification yourself.

Best Regards,

Jiale

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Sanket Joshi 20 Reputation points

2025-01-23T04:39:31.1666667+00:00

Hi

Thank you for your reply. But your code is not working for me and giving exception if null tag is passed.

Can you please help.

Also our is windows application built in .net framework 4.7.2.

Will it work there ? If not then .net core ?

If yes than can i build library .net core and use it in my windows application
Sanket Joshi 20 Reputation points

2025-01-23T04:42:19.3833333+00:00

not working for me and giving this error if null tag is passed
Sanket Joshi 20 Reputation points

2025-01-23T04:43:21.6166667+00:00

image.png
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Anonymous

2025-01-23T13:07:02.15+00:00

Sorry , Tag is an integral part of AES-GCM mode, which is one of the core design principles of AES-GCM.

Sanket Joshi 20

Then we are badly stuck. The server side is in C++ which does not use tag and they have shared us code snipped which we have compiled in VC++ and created dll which we have used in C# windows application through import loads.

It is working but it is giving lot of latency issues in encryption and decryption because of which our application performance has deteriorated.
Can we convert the C++ code in C# and any tool to do it or what do we do to increase performance

// AESGCMEncryptor.cpp

#include "pch.h"

#include <openssl/evp.h>

#include <openssl/rand.h>

#include <cstring>

#include <iostream>

#include <vector>

#include "AesGcm32Release.h"

using std::string;

using std::vector;

using std::cout;

unsigned char g_key[32];

unsigned char g_iv[12];

EVP_CIPHER_CTX* d_ctx = EVP_CIPHER_CTX_new();

EVP_CIPHER_CTX* e_ctx = EVP_CIPHER_CTX_new();

extern "C" {

__declspec(dllexport) void SetKeyAndIV(unsigned char* key, unsigned char* iv)

{

    memcpy(g_key, key, 32);

    memcpy(g_iv, iv, 12);

    EVP_DecryptInit(d_ctx, EVP_aes_256_gcm(), g_key, g_iv);

    EVP_EncryptInit(e_ctx, EVP_aes_256_gcm(), g_key, g_iv);

}

__declspec(dllexport) unsigned char* AESGCMEncrypt(const unsigned char* plaintext, int plaintext_len, const unsigned char* key, const unsigned char* iv, int* ciphertext_len)

{

    unsigned char* ciphertext = aes_256_gcm_encrypt(plaintext, plaintext_len, e_ctx, ciphertext_len);

    return ciphertext;

}

__declspec(dllexport) unsigned char* AESGCMDecrypt(const unsigned char* ciphertext, int ciphertext_len, const unsigned char* key, const unsigned char* iv, int* plaintext_len)

{

    unsigned char* plaintext = aes_256_gcm_decrypt(ciphertext, ciphertext_len, d_ctx, plaintext_len);

    return plaintext;

}

unsigned char* aes_256_gcm_encrypt(const unsigned  char* plaintext, int size, EVP_CIPHER_CTX* e_ctx, int* ciphertext_len)

{

    std::vector<unsigned char>ciphertext(size);

    int len;

    int actual_size = 0, final_size = 0;

    EVP_EncryptUpdate(e_ctx, ciphertext.data(), &len, plaintext, size);

    int ciphertext_length = len;

    *ciphertext_len = ciphertext_length;

    unsigned char* output = new unsigned char[ciphertext_length];

    std::memcpy(output, ciphertext.data(), ciphertext_length);

    return output;

}

unsigned char* aes_256_gcm_decrypt(const unsigned char* ciphertext, int size, EVP_CIPHER_CTX* d_ctx, int* plaintext_len)

{

    std::vector<unsigned char>plaintext(size);

    int len;

    int actual_size = 0, final_size = 0;

    EVP_DecryptUpdate(d_ctx, plaintext.data(), &len, ciphertext, size);

    int plaintext_length = len;

    *plaintext_len = plaintext_length;

    unsigned char* output = new unsigned char[plaintext_length];

    std::memcpy(output, plaintext.data(), plaintext_length);

    return output;

}

}

#pragma once

#ifndef AESGCM_H

#define AESGCM_H

#include <openssl/evp.h>

#include <openssl/aes.h>

#include <vector>

extern "C" __declspec(dllexport) void SetKeyAndIV(unsigned char* key, unsigned char* iv);

extern "C" __declspec(dllexport) unsigned char* aes_256_gcm_encrypt(const unsigned char* plaintext, int size, EVP_CIPHER_CTX * e_ctx, int* ciphertext_len);

extern "C" __declspec(dllexport) unsigned char* aes_256_gcm_decrypt(const unsigned char* ciphertext, int size, EVP_CIPHER_CTX * d_ctx, int* plaintext_len);

extern "C" __declspec(dllexport) unsigned char* AESGCMEncrypt(const unsigned char* plaintext, int plaintext_len, const unsigned char* key, const unsigned char* iv, int* ciphertext_len);

extern "C" __declspec(dllexport) unsigned char* AESGCMDecrypt(const unsigned char* ciphertext, int ciphertext_len, const unsigned char* key, const unsigned char* iv, int* plaintext_len);

#endif

// dllmain.cpp : Defines the entry point for the DLL application.

#include "pch.h"

BOOL APIENTRY DllMain( HMODULE hModule,

                   DWORD  ul_reason_for_call,

                   LPVOID lpReserved

                 )

{

switch (ul_reason_for_call)

{

case DLL_PROCESS_ATTACH:

case DLL_THREAD_ATTACH:

case DLL_THREAD_DETACH:

case DLL_PROCESS_DETACH:

    break;

}

return TRUE;

}

#pragma once

#define WIN32_LEAN_AND_MEAN // Exclude rarely-used stuff from Windows headers

// Windows Header Files

#include <windows.h>

// pch.cpp: source file corresponding to the pre-compiled header

#include "pch.h"

// When you are using pre-compiled headers, this source file is necessary for compilation to succeed.

<?xml version="1.0" encoding="utf-8"?>

<ProjectConfiguration Include="Debug|Win32">

  <Configuration>Debug</Configuration>

  <Platform>Win32</Platform>

</ProjectConfiguration>

<ProjectConfiguration Include="Release|Win32">

  <Configuration>Release</Configuration>

  <Platform>Win32</Platform>

</ProjectConfiguration>

<ProjectConfiguration Include="Debug|x64">

  <Configuration>Debug</Configuration>

  <Platform>x64</Platform>

</ProjectConfiguration>

<ProjectConfiguration Include="Release|x64">

  <Configuration>Release</Configuration>

  <Platform>x64</Platform>

</ProjectConfiguration>

</ItemGroup>

<VCProjectVersion>16.0</VCProjectVersion>

<Keyword>Win32Proj</Keyword>

<ProjectGuid>{4a9c7ebc-3e85-4ed3-86ed-be3904fdfc00}</ProjectGuid>

<RootNamespace>AesGcm32Release</RootNamespace>

<WindowsTargetPlatformVersion>10.0</WindowsTargetPlatformVersion>

</PropertyGroup>

<ConfigurationType>DynamicLibrary</ConfigurationType>

<UseDebugLibraries>true</UseDebugLibraries>

<PlatformToolset>v142</PlatformToolset>

<CharacterSet>Unicode</CharacterSet>

</PropertyGroup>

<ConfigurationType>DynamicLibrary</ConfigurationType>

<UseDebugLibraries>false</UseDebugLibraries>

<PlatformToolset>v142</PlatformToolset>

<WholeProgramOptimization>true</WholeProgramOptimization>

<CharacterSet>Unicode</CharacterSet>

</PropertyGroup>

<ConfigurationType>DynamicLibrary</ConfigurationType>

<UseDebugLibraries>true</UseDebugLibraries>

<PlatformToolset>v142</PlatformToolset>

<CharacterSet>Unicode</CharacterSet>

</PropertyGroup>

<ConfigurationType>DynamicLibrary</ConfigurationType>

<UseDebugLibraries>false</UseDebugLibraries>

<PlatformToolset>v142</PlatformToolset>

<WholeProgramOptimization>true</WholeProgramOptimization>

<CharacterSet>Unicode</CharacterSet>

</PropertyGroup>

</ImportGroup>

</ImportGroup>

<Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />

</ImportGroup>

<Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />

</ImportGroup>

<Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />

</ImportGroup>

<Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />

</ImportGroup>

<LinkIncremental>true</LinkIncremental>

</PropertyGroup>

<LinkIncremental>false</LinkIncremental>

<IncludePath>C:\Program Files (x86)\OpenSSL-Win32\include</IncludePath>

</PropertyGroup>

<LinkIncremental>true</LinkIncremental>

</PropertyGroup>

<LinkIncremental>false</LinkIncremental>

</PropertyGroup>

<ClCompile>

  <WarningLevel>Level3</WarningLevel>

  <SDLCheck>true</SDLCheck>

  <PreprocessorDefinitions>WIN32;_DEBUG;AESGCM32RELEASE_EXPORTS;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>

  <ConformanceMode>true</ConformanceMode>

  <PrecompiledHeader>Use</PrecompiledHeader>

  <PrecompiledHeaderFile>pch.h</PrecompiledHeaderFile>

</ClCompile>

<Link>

  <SubSystem>Windows</SubSystem>

  <GenerateDebugInformation>true</GenerateDebugInformation>

  <EnableUAC>false</EnableUAC>

</Link>

</ItemDefinitionGroup>

<ClCompile>

  <WarningLevel>Level3</WarningLevel>

  <FunctionLevelLinking>true</FunctionLevelLinking>

  <IntrinsicFunctions>true</IntrinsicFunctions>

  <SDLCheck>true</SDLCheck>

  <PreprocessorDefinitions>WIN32;NDEBUG;AESGCM32RELEASE_EXPORTS;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>

  <ConformanceMode>true</ConformanceMode>

  <PrecompiledHeader>Use</PrecompiledHeader>

  <PrecompiledHeaderFile>pch.h</PrecompiledHeaderFile>

</ClCompile>

<Link>

  <SubSystem>Windows</SubSystem>

  <EnableCOMDATFolding>true</EnableCOMDATFolding>

  <OptimizeReferences>true</OptimizeReferences>

  <GenerateDebugInformation>true</GenerateDebugInformation>

  <EnableUAC>false</EnableUAC>

  <AdditionalLibraryDirectories>C:\Program Files (x86)\OpenSSL-Win32\lib\VC\x86\MD</AdditionalLibraryDirectories>

  <AdditionalDependencies>libssl.lib;libcrypto.lib;%(AdditionalDependencies)</AdditionalDependencies>

</Link>

</ItemDefinitionGroup>

<ClCompile>

  <WarningLevel>Level3</WarningLevel>

  <SDLCheck>true</SDLCheck>

  <PreprocessorDefinitions>_DEBUG;AESGCM32RELEASE_EXPORTS;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>

  <ConformanceMode>true</ConformanceMode>

  <PrecompiledHeader>Use</PrecompiledHeader>

  <PrecompiledHeaderFile>pch.h</PrecompiledHeaderFile>

</ClCompile>

<Link>

  <SubSystem>Windows</SubSystem>

  <GenerateDebugInformation>true</GenerateDebugInformation>

  <EnableUAC>false</EnableUAC>

</Link>

</ItemDefinitionGroup>

<ClCompile>

  <WarningLevel>Level3</WarningLevel>

  <FunctionLevelLinking>true</FunctionLevelLinking>

  <IntrinsicFunctions>true</IntrinsicFunctions>

  <SDLCheck>true</SDLCheck>

  <PreprocessorDefinitions>NDEBUG;AESGCM32RELEASE_EXPORTS;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>

  <ConformanceMode>true</ConformanceMode>

  <PrecompiledHeader>Use</PrecompiledHeader>

  <PrecompiledHeaderFile>pch.h</PrecompiledHeaderFile>

</ClCompile>

<Link>

  <SubSystem>Windows</SubSystem>

  <EnableCOMDATFolding>true</EnableCOMDATFolding>

  <OptimizeReferences>true</OptimizeReferences>

  <GenerateDebugInformation>true</GenerateDebugInformation>

  <EnableUAC>false</EnableUAC>

</Link>

</ItemDefinitionGroup>

<ClInclude Include="AesGcm32Release.h" />

<ClInclude Include="framework.h" />

<ClInclude Include="pch.h" />

</ItemGroup>

<ClCompile Include="AesGcm32Release.cpp" />

<ClCompile Include="dllmain.cpp" />

<ClCompile Include="pch.cpp">

  <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">Create</PrecompiledHeader>

  <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">Create</PrecompiledHeader>

  <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">Create</PrecompiledHeader>

  <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Release|x64'">Create</PrecompiledHeader>

</ClCompile>

</ItemGroup>

</ImportGroup>

</Project>

<?xml version="1.0" encoding="utf-8"?>

<Filter Include="Source Files">

  <UniqueIdentifier>{4FC737F1-C7A5-4376-A066-2A32D752A2FF}</UniqueIdentifier>

  <Extensions>cpp;c;cc;cxx;c++;cppm;ixx;def;odl;idl;hpj;bat;asm;asmx</Extensions>

</Filter>

<Filter Include="Header Files">

  <UniqueIdentifier>{93995380-89BD-4b04-88EB-625FBE52EBFB}</UniqueIdentifier>

  <Extensions>h;hh;hpp;hxx;h++;hm;inl;inc;ipp;xsd</Extensions>

</Filter>

<Filter Include="Resource Files">

  <UniqueIdentifier>{67DA6AB6-F800-4c08-8B7A-83BB121AAD01}</UniqueIdentifier>

  <Extensions>rc;ico;cur;bmp;dlg;rc2;rct;bin;rgs;gif;jpg;jpeg;jpe;resx;tiff;tif;png;wav;mfcribbon-ms</Extensions>

</Filter>

</ItemGroup>

<ClInclude Include="framework.h">

  <Filter>Header Files</Filter>

</ClInclude>

<ClInclude Include="pch.h">

  <Filter>Header Files</Filter>

</ClInclude>

<ClInclude Include="AesGcm32Release.h">

  <Filter>Header Files</Filter>

</ClInclude>

</ItemGroup>

<ClCompile Include="dllmain.cpp">

  <Filter>Source Files</Filter>

</ClCompile>

<ClCompile Include="pch.cpp">

  <Filter>Source Files</Filter>

</ClCompile>

<ClCompile Include="AesGcm32Release.cpp">

  <Filter>Source Files</Filter>

</ClCompile>

</ItemGroup>

</Project>

<?xml version="1.0" encoding="utf-8"?>

</Project>

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Anonymous

2025-01-24T12:26:02.2366667+00:00

Sorry, QA cannot help you optimize your C++ DLL.

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How to implement AES GCM 256 bytes with Key & IV but without using the tag in C# 4.7.2 or any .net version

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