How to install an assembly into the Global Assembly Cache in Visual C#

For a Microsoft Visual Basic .NET version of this article, see
315682 .



This article describes how to generate a strong name for an assembly, and how to install a .dll file in the Global Assembly Cache (GAC). With the GAC, you can share assemblies across many applications. The GAC is automatically installed with the .NET runtime. Components are typically stored in C:\WINNT\Assembly.

To install an assembly in the GAC, you must give the assembly a strong name. The name is a cryptographic hash-key, or signature. This strong name ensures correct component versioning. This helps prevent components that have the same name from conflicting with each other, or from being incorrectly used by a consuming application.

back to the top


The following list outlines the recommended hardware, software, network infrastructure, and service packs that are required:
  • Administrator rights to the computer where the shared assembly is being installed

This article assumes that you are familiar with the following topics:
  • General familiarity with assemblies in .NET.
  • General familiarity with the use of tools at the command prompt.
back to the top

Global Assembly Cache

To create a small Class Library project by using Visual Studio, to generate a strong name, and to install the .dll file of the project in the GAC, follow these steps:
  1. In Visual Studio, create a new Visual C# Class Library project, and name the project
  2. You must use a strong name. To generate this cryptographic key pair, use the SN Tool. This tool is located in the \bin subdirectory where the .NET Framework Solution Developer Kit (SDK) is installed. The SN Tool is easy to use. The command-line statement takes the following
    sn -k "[DriveLetter]:\[DirectoryToPlaceKey]\[KeyName].snk"
    Note In Visual Studio 2005 and in later versions of Visual Studio, you can use the IDE project properties to generate a key pair and sign your assembly. Then, you can skip step 3 and step 4 and also skip making any code changes to the AssemblyInfo.cs file.

    To use the IDE project properties to generate a key pair and sign your assembly, follow these steps:
    1. In Solution Explorer, right-click GACDemo, and then click Properties.
    2. Click the Signing tab, and then click to select the Sign the assembly check box.
    3. In the Choose a strong name key list, click <New...>.
    4. Type GACkey.snk as the key file name, click to clear the Protect my key file with a password check box, and then click OK.
    5. Press CTRL+SHIFT+B to compile the project.
    After you follow these steps, you still must follow step 5 to install your assembly in the GAC.
  3. Create a directory named GACKey in C:\ so that you can easily locate the key, and access the key at the command prompt.

    Note For most users, the .NET tools are located in C:\Program Files\Microsoft.NET\FrameworkSDK\Bin. Before you type the following SN command, you may want to copy this similar path on your computer to the .NET bin directory. Type cd at the command prompt, right-click to paste the path, and then press ENTER to quickly change to the directory where the SN Tool is located.

    Type the following:
    sn -k "C:\GACKey\GACkey.snk"
  4. A key is generated, but it is not yet associated with the assembly of the project. To create this association, double-click the AssemblyInfo.cs file in Visual Studio .NET Solution Explorer. This file has the list of assembly attributes that are included by default when a project is created in Visual Studio .NET. Modify the AssemblyKeyFileassembly attribute in the code as follows:
    [assembly: AssemblyKeyFile("C:\\GACKey\\GACKey.snk")]
    Compile the project by clicking CTRL+SHIFT+B. You do not have to have any additional code to install a .dll file in the GAC.
  5. You can install the .dll file by using the Gacutil tool or by dragging the .dll file to the appropriate folder. If you use the Gacutil tool, you can use a command that resembles the following:
    gacutil -I "[DriveLetter]:\[PathToBinDirectoryInVSProject]\gac.dll"
    To drag the file, open two instances of Windows Explorer. In one instance, find the location of the .dll file output for your console project. In the other instance, find c:\[SystemRoot]\Assembly. Then, drag your .dll file to the
    Assembly folder.
back to the top

Complete code listing (AssemblyInfo.cs)

using System.Reflection;
using System.Runtime.CompilerServices;

// General Information about an assembly is controlled through the following
// set of attributes. Change these attribute values to modify the information
// that is associated with an assembly.
[assembly: AssemblyTitle("")]
[assembly: AssemblyDescription("")]
[assembly: AssemblyConfiguration("")]
[assembly: AssemblyCompany("")]
[assembly: AssemblyProduct("")]
[assembly: AssemblyCopyright("")]
[assembly: AssemblyTrademark("")]
[assembly: AssemblyCulture("")]

// Version information for an assembly is made up of the following four values:
// Major Version
// Minor Version
// Build Number
// Revision
// You can specify all the values, or you can default the revision and build numbers
// by using the '*' as shown below:

[assembly: AssemblyVersion("1.0.*")]

// To sign your assembly you must specify a key to use. See the
// Microsoft .NET Framework documentation for more information about assembly signing.
// Use the following attributes to control that key is used for signing.
// Notes:
// (*) If no key is specified, the assembly is not signed.
// (*) KeyName refers to a key that has been installed in the Crypto Service
// Provider (CSP) on your computer. KeyFile refers to a file that contains
// a key.
// (*) If the KeyFile and the KeyName values are both specified, the
// following processing occurs:
// (1) If the KeyName can be found in the CSP, that key is used.
// (2) If the KeyName does not exist and the KeyFile does exist, the key
// in the KeyFile is installed to the CSP and used.
// (*) To create a KeyFile, you can use the sn.exe (Strong Name) utility.
// When specifying the KeyFile, the location of the KeyFile must be
// relative to the project output directory which is
// %Project Directory%\obj\<configuration>. For example, if your KeyFile is
// located in the project directory, you would specify the AssemblyKeyFile
// attribute as [assembly: AssemblyKeyFile("..\\..\\mykey.snk")]
// (*) Delay Signing is an advanced option - see the Microsoft .NET Framework
// documentation for more information about this.
[assembly: AssemblyDelaySign(false)]
[assembly: AssemblyKeyFile("C:\\GACKey\\GACKey.snk")]
[assembly: AssemblyKeyName("")]
back to the top


  1. Start Windows Explorer.
  2. Locate C:\SystemRoot\ assembly.
  3. You see GACDemo in the list of installed .dll files.
back to the top


For more information, see the following Microsoft Web sites:
Installing an assembly into the Global Assembly Cache
back to the top