ClickOnce Security and Deployment

ClickOnce is a deployment technology that enables you to create self-updating Windows-based applications that can be installed and run with minimal user interaction. Visual Studio provides full support for publishing and updating applications deployed with ClickOnce technology if you have developed your projects with Visual Basic and Visual C#. For information about deploying Visual C++ applications, see ClickOnce Deployment for Visual C++ Applications.

ClickOnce deployment overcomes three major issues in deployment:

• Difficulties in updating applications. With Microsoft Windows Installer deployment, whenever an application is updated, the user can install an update, an msp file, and apply it to the installed product; with ClickOnce deployment, you can provide updates automatically. Only those parts of the application that have changed are downloaded, and then the full, updated application is reinstalled from a new side-by-side folder.

• Impact to the user's computer. With Windows Installer deployment, applications often rely on shared components, with the potential for versioning conflicts; with ClickOnce deployment, each application is self-contained and cannot interfere with other applications.

• Security permissions. Windows Installer deployment requires administrative permissions and allows only limited user installation; ClickOnce deployment enables non-administrative users to install and grants only those Code Access Security permissions necessary for the application.

  In the past, these issues sometimes caused developers to decide to create Web applications instead of Windows-based applications, sacrificing a rich user interface for ease of installation. By using applications deployed using ClickOnce, you can have the best of both technologies.

What Is a ClickOnce Application?

A ClickOnce application is any Windows Presentation Foundation (.xbap), Windows Forms (.exe), console application (.exe), or Office solution (.dll) published using ClickOnce technology. You can publish a ClickOnce application in three different ways: from a Web page, from a network file share, or from media such as a CD-ROM. A ClickOnce application can be installed on an end user's computer and run locally even when the computer is offline, or it can be run in an online-only mode without permanently installing anything on the end user's computer. For more information, see Choosing a ClickOnce Deployment Strategy.

ClickOnce applications can be self-updating; they can check for newer versions as they become available and automatically replace any updated files. The developer can specify the update behavior; a network administrator can also control update strategies, for example, marking an update as mandatory. Updates can also be rolled back to an earlier version by the end user or by an administrator. For more information, see Choosing a ClickOnce Update Strategy.

Because ClickOnce applications are isolated, installing or running a ClickOnce application cannot break existing applications. ClickOnce applications are self-contained; each ClickOnce application is installed to and run from a secure per-user, per-application cache. ClickOnce applications run in the Internet or Intranet security zones. If necessary, the application can request elevated security permissions. For more information, see Securing ClickOnce Applications.

How ClickOnce Security Works

The core ClickOnce security is based on certificates, code access security policies, and the ClickOnce trust prompt.

Certificates

Authenticode certificates are used to verify the authenticity of the application's publisher. By using Authenticode for application deployment, ClickOnce helps prevent a harmful program from portraying itself as a legitimate program coming from an established, trustworthy source. Optionally, certificates can also be used to sign the application and deployment manifests to prove that the files have not been tampered with. For more information, see ClickOnce and Authenticode. Certificates can also be used to configure client computers to have a list of trusted publishers. If an application comes from a trusted publisher, it can be installed without any user interaction. For more information, see Trusted Application Deployment Overview.

Code Access Security

Code access security helps limit the access that code has to protected resources. In most cases, you can choose the Internet or Local Intranet zones to limit the permissions. Use the Security page in the ProjectDesigner to request the zone appropriate for the application. You can also debug applications with restricted permissions to emulate the end-user experience. For more information, see Code Access Security for ClickOnce Applications.

ClickOnce Trust Prompt

If the application requests more permissions than the zone allows, the end user can be prompted to make a trust decision. The end user can decide if ClickOnce applications such as Windows Forms applications, Windows Presentation Foundation applications, console applications, XAML browser applications, and Office solutions are trusted to run. For more information, see How to: Configure the ClickOnce Trust Prompt Behavior.

How ClickOnce Deployment Works

The core ClickOnce deployment architecture is based on two XML manifest files: an application manifest and a deployment manifest. The files are used to describe where the ClickOnce applications are installed from, how they are updated, and when they are updated.

Publishing ClickOnce Applications

The application manifest describes the application itself. This includes the assemblies, the dependencies and files that make up the application, the required permissions, and the location where updates will be available. The application developer authors the application manifest by using the Publish Wizard in Visual Studio or the Manifest Generation and Editing Tool (Mage.exe) in the Windows Software Development Kit (SDK). For more information, see How to: Publish a ClickOnce Application using the Publish Wizard.

The deployment manifest describes how the application is deployed. This includes the location of the application manifest, and the version of the application that clients should run.

Deploying ClickOnce Applications

After it is created, the deployment manifest is copied to the deployment location. This can be a Web server, network file share, or media such as a CD. The application manifest and all the application files are also copied to a deployment location that is specified in the deployment manifest. This can be the same as the deployment location, or it can be a different location. When using the Publish Wizard in Visual Studio, the copy operations are performed automatically.

Installing ClickOnce Applications

After it is deployed to the deployment location, end users can download and install the application by clicking an icon representing the deployment manifest file on a Web page or in a folder. In most cases, the end user is presented with a simple dialog box asking the user to confirm installation, after which installation proceeds and the application is started without additional intervention. In cases where the application requires elevated permissions or if the application is not signed by a trusted certificate, the dialog box also asks the user to grant permission before the installation can continue. Though ClickOnce installs are per-user, permission elevation may be required if there are prerequisites that require administrator privileges. For more information about elevated permissions, see Securing ClickOnce Applications.

Certificates can be trusted at the machine or enterprise level, so that ClickOnce applications signed with a trusted certificate can install silently. For more information about trusted certificates, see Trusted Application Deployment Overview.

The application can be added to the user's Start menu and to the Add or Remove Programs group in the Control Panel. Unlike other deployment technologies, nothing is added to the Program Files folder or the registry, and no administrative rights are required for installation

Updating ClickOnce Applications

When the application developers create an updated version of the application, they generate a new application manifest and copy files to a deployment location—usually a sibling folder to the original application deployment folder. The administrator updates the deployment manifest to point to the location of the new version of the application.

In addition to the deployment location, the deployment manifest also contains an update location (a Web page or network file share) where the application checks for updated versions. ClickOnce Publish properties are used to specify when and how often the application should check for updates. Update behavior can be specified in the deployment manifest, or it can be presented as user choices in the application's user interface by means of the ClickOnce APIs. In addition, Publish properties can be employed to make updates mandatory or to roll back to an earlier version. For more information, see Choosing a ClickOnce Update Strategy.

Third Party Installers

You can customize your ClickOnce installer to install third-party components along with your application. You must have the redistributable package (.exe or .msi file) and describe the package with a language-neutral product manifest and a language-specific package manifest. For more information, see Creating Bootstrapper Packages.

ClickOnce Tools

The following table shows the tools that you can use to generate, edit, sign, and re-sign the application and deployment manifests.

The following table shows the .NET Framework version required to support ClickOnce applications in these browsers.

See Also

ClickOnce Deployment on Windows Vista
Publishing ClickOnce Applications
Securing ClickOnce Applications
Deploying COM Components with ClickOnce
Building ClickOnce Applications from the Command Line
Debugging ClickOnce Applications That Use System.Deployment.Application