# How to: Create a public-private key pair

To sign an assembly with a strong name, you must have a public/private key pair. This public and private cryptographic key pair is used during compilation to create a strong-named assembly. You can create a key pair using the Strong Name tool (Sn.exe). Key pair files usually have an .snk extension.

Note

In Visual Studio, the C# and Visual Basic project property pages include a Signing tab that enables you to select existing key files or to generate new key files without using Sn.exe. In Visual C++, you can specify the location of an existing key file in the Advanced property page in the Linker section of the Configuration Properties section of the Property Pages window. The use of the AssemblyKeyFileAttribute attribute to identify key file pairs was made obsolete beginning with Visual Studio 2005.

## Create a key pair

To create a key pair, at a command prompt, type the following command:

sn –k <file name>

In this command, file name is the name of the output file containing the key pair.

The following example creates a key pair called sgKey.snk.

sn -k sgKey.snk


If you intend to delay sign an assembly and you control the whole key pair (which is unlikely outside test scenarios), you can use the following commands to generate a key pair and then extract the public key from it into a separate file. First, create the key pair:

sn -k keypair.snk


Next, extract the public key from the key pair and copy it to a separate file:

sn -p keypair.snk public.snk


Once you create the key pair, you must put the file where the strong name signing tools can find it.

When signing an assembly with a strong name, the Assembly Linker (Al.exe) looks for the key file relative to the current directory and to the output directory. When using command-line compilers, you can simply copy the key to the current directory containing your code modules.

If you are using an earlier version of Visual Studio that does not have a Signing tab in the project properties, the recommended key file location is the project directory with the file attribute specified as follows:

[assembly:AssemblyKeyFileAttribute("keyfile.snk")];

[assembly:AssemblyKeyFileAttribute("keyfile.snk")]

<Assembly:AssemblyKeyFileAttribute("keyfile.snk")>