Digitally Signed Software

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Software that is downloaded from the Internet to users' computers can contain programs such as viruses and Trojan horses that are designed to cause malicious damage or provide clandestine network access to intruders. As networks become more interconnected, malicious software and viruses also become a threat to intranets. To help counter this growing threat, you can digitally sign the software that you distribute on your intranets or the Internet to ensure its integrity and to assure others that the software can be trusted. Signed software ensures that users can verify the origin of the software, as well as verify that no one has tampered with it.

Microsoft developed the Microsoft® Authenticode® technology, which enables developers to digitally sign software. The last thing developers do before they release software is digitally sign the software. Any modification to the software after it is signed invalidates the digital signature. By using Authenticode technology, code signers who own valid X.509 version 3 code-signing certificates can sign software with their private key. Several other third-party code signing technologies also use digital certificates to enable code signing.

Code Signing Within Your Organization

Executable programs, scripts, and ActiveX® controls that are distributed in Windows 2000 domains should be digitally signed by trusted developers. To protect your network from malicious programs and viruses, you can configure Internet Explorer to specify security settings for the Internet, local intranet, Trusted sites, and Restricted sites security zones. You can specify security settings that prevent users from downloading and running unsigned software from any security zone. You can also configure Internet Explorer to trust specific software publishers so that any software that is signed by these publishers is downloaded automatically without notifying the users. For more information about Internet Explorer security, see the Microsoft ® Windows ®  2000 Server Resource Kit Internet Explorer Resource Guide .

In addition, you can configure Public Key Group Policy to specify the CAs for code signing that are trusted in your organization. You can trust software publishing certificates that are issued either by commercial CAs or by your CAs. You can also create and use CTLs to establish trust in the domain for code-signing certificates.

You can use Certificate Services to issue code-signing certificates to the developers who sign software for distribution on your intranet.

Code Signing on the Internet

When software is distributed over the Internet, users are more likely to trust software that is signed by a publisher whose code-signing certificates ("software publisher certificates") have been issued by a reputable commercial CA. Using commercial CAs also removes the liability placed on your organization when you assume the responsibilities of a commercial CA for external software distribution. Therefore, if you distribute software on the Internet, consider obtaining the services of a commercial CA to issue digital signing certificates to your external software developers.

Consider providing special protection for the private keys that are used to sign code. If someone obtains access to a private key for code signing, they can impersonate your organization, distribute signed but defective or malicious code, and damage your organization's reputation. Some third-party vendors offer smart card solutions that enable code signing with smart cards. You can establish a smart card program for code signers that provides additional protection for their private keys.

Automating Code Signing and Software Distribution

You can build custom applications to automate code signing and the distribution of software within your organization or to external Web sites. Internal and external developers or program managers who have valid code-signing certificates can use custom applications to submit code to be signed automatically and processed for distribution. Deploying code-signing applications includes the following activities:

  • Installing CAs that issue code-signing certificates or obtaining certificate services from a commercial CA.

  • Developing the custom applications for code signing and software distribution.

  • Issuing code-signing certificates to the appropriate developers or program managers.

  • Configuring the software distribution infrastructure and services.

For example, you might use Active Server Pages (ASP) technology and Internet Information Services to build code-signing and software distribution Web sites. You might configure one-to-one certificate mapping to grant permission for use of the Web site to users who have valid code-signing certificates. Users who do not have valid code-signing certificates are not permitted to use the site to submit code for signing and distribution.