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Create a certificate for package signing

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This article explains how to create and export a certificate for app package signing using PowerShell tools. It's recommended that you use Visual Studio for packaging UWP apps and packaging desktop apps, but you can still package an app manually if you did not use Visual Studio to develop your app.

Prerequisites

  • A packaged or unpackaged app
    An app containing an AppxManifest.xml file. You will need to reference the manifest file while creating the certificate that will be used to sign the final app package. For details on how to manually package an app, see Create an app package with the MakeAppx.exe tool.

  • Public Key Infrastructure (PKI) Cmdlets
    You need PKI cmdlets to create and export your signing certificate. For more information, see Public Key Infrastructure Cmdlets.

Create a self-signed certificate

A self-signed certificate is useful for testing your app before you're ready to publish it to the Store. Follow the steps outlined in this section to create a self-signed certificate.

Note

When you create and use a self-signed certificate only users who install and trust your certificate can run your application. This is easy to implement for testing but it may prevent additional users from installing your application. When you are ready to publish your application we recommend that you use a certificate issued by a trusted source. This system of centralized trust helps to ensure that the application ecosystem has levels of verification to protect users from malicious actors.

Determine the subject of your packaged app

To use a certificate to sign your app package, the "Subject" in the certificate must match the "Publisher" section in your app's manifest.

For example, the "Identity" section in your app's AppxManifest.xml file should look something like this:

  <Identity Name="Contoso.AssetTracker" 
    Version="1.0.0.0" 
    Publisher="CN=Contoso Software, O=Contoso Corporation, C=US"/>

The "Publisher", in this case, is "CN=Contoso Software, O=Contoso Corporation, C=US" which needs to be used for creating your certificate.

Use New-SelfSignedCertificate to create a certificate

Use the New-SelfSignedCertificate PowerShell cmdlet to create a self signed certificate. New-SelfSignedCertificate has several parameters for customization, but for the purpose of this article, we'll focus on creating a simple certificate that will work with SignTool. For more examples and uses of this cmdlet, see New-SelfSignedCertificate.

Based on the AppxManifest.xml file from the previous example, you should use the following syntax to create a certificate. In an elevated PowerShell prompt:

New-SelfSignedCertificate -Type Custom -Subject "CN=Contoso Software, O=Contoso Corporation, C=US" -KeyUsage DigitalSignature -FriendlyName "Your friendly name goes here" -CertStoreLocation "Cert:\CurrentUser\My" -TextExtension @("2.5.29.37={text}1.3.6.1.5.5.7.3.3", "2.5.29.19={text}")

Note the following details about some of the parameters:

  • KeyUsage: This parameter defines what the certificate may be used for. For a self-signing certificate, this parameter should be set to DigitalSignature.

  • TextExtension: This parameter includes settings for the following extensions:

    • Extended Key Usage (EKU): This extension indicates additional purposes for which the certified public key may be used. For a self-signing certificate, this parameter should include the extension string "2.5.29.37={text}1.3.6.1.5.5.7.3.3", which indicates that the certificate is to be used for code signing.

    • Basic Constraints: This extension indicates whether or not the certificate is a Certificate Authority (CA). For a self-signing certificate, this parameter should include the extension string "2.5.29.19={text}", which indicates that the certificate is an end entity (not a CA).

After running this command, the certificate will be added to the local certificate store, as specified in the "-CertStoreLocation" parameter. The result of the command will also produce the certificate's thumbprint.

You can view your certificate in a PowerShell window by using the following commands:

Set-Location Cert:\CurrentUser\My
Get-ChildItem | Format-Table Subject, FriendlyName, Thumbprint

This will display all of the certificates in your local store.

Export a certificate

To export the certificate in the local store to a Personal Information Exchange (PFX) file, use the Export-PfxCertificate cmdlet.

When using Export-PfxCertificate, you must either create and use a password or use the "-ProtectTo" parameter to specify which users or groups can access the file without a password. Note that an error will be displayed if you don't use either the "-Password" or "-ProtectTo" parameter.

Password usage

$password = ConvertTo-SecureString -String <Your Password> -Force -AsPlainText 
Export-PfxCertificate -cert "Cert:\CurrentUser\My\<Certificate Thumbprint>" -FilePath <FilePath>.pfx -Password $password

ProtectTo usage

Export-PfxCertificate -cert Cert:\CurrentUser\My\<Certificate Thumbprint> -FilePath <FilePath>.pfx -ProtectTo <Username or group name>

After you create and export your certificate, you're ready to sign your app package with SignTool. For the next step in the manual packaging process, see Sign an app package using SignTool.

Security considerations

By adding a certificate to local machine certificate stores, you affect the certificate trust of all users on the computer. It is recommended that you remove those certificates when they are no longer necessary to prevent them from being used to compromise system trust.