Home > Articles > Programming > Windows Programming

This chapter is from the book

Public Keys and Assemblies

The CLR uses public key technology both to uniquely identify the developer of a component and to protect the component from being tampered with once it is out of the original developer's hands. Each assembly can have a public key embedded in its manifest that identifies the developer. Assemblies with public keys also have a digital signature that is generated before the assembly is first shipped that provides a secure hash of the assembly manifest, which itself contains hashes of all subordinate modules. This ensures that once the assembly ships, no one can modify the code or other resources contained in the assembly. This digital signature can be verified using only the public key; however, the signature can be generated only with the corresponding private key, which organizations must guard more closely than their source code. The current builds of the CLR use RSA public/private keys and Secure Hash Algorithm (SHA) hashing to produce the digital signature. Although the private key used to sign the assembly is a unique fingerprint for each organization, it does not provide the same level of nonrepudiation that digital certificates provide. For example, there is no way to look up the developer's identity based solely on an assembly's public key. The CLR does provide support for embedding digital certificates into assemblies, but that is outside the scope of this chapter (for more information, see Chapter 9).

The .NET SDK ships with a tool (SN.EXE) that simplifies working with public and private keys during development and deployment. Running SN.EXE with the -k option creates a new file that contains a newly generated public/private key pair. This file contains your private key, so it is critical that you practice safe computing and do not leave this file in an unsecured location. Because the private key is so critical, most organizations postpone the actual signing of the assembly until just before shipping, a practice called delay signing. To allow all developers in an organization to access the public key without having access to the private key, SN.EXE supports removing the private key portion using the -p option. This option creates a new file that contains only the public key. The conventional file extension for both public/private and public-only key files is .SNK.

The public key produced by SN.EXE is a 128-byte opaque algorithm-specific structure with an additional 32 bytes of header information. To keep the size of assembly references (and their display names) compact, an assembly reference can use a public key token, which is an 8-byte hash of the full public key. The assembly references emitted by most compilers use this token in lieu of the full public key to keep the overall size of the manifest small. You can calculate the token for a public key by using SN.EXE's -t or -T options. The former calculates the token based on an .SNK file containing only a public key. The latter calculates the token based on a public key stored in an assembly's manifest. Figure 2.6 shows the SN.EXE tool in action.

Figure 6Figure 2.6: Managing Public/Private Keys Using SN.EXE

Development tools that support the CLR must provide some mechanism for developers to sign their assemblies, either via custom attributes or command-line switches. The System.Reflection.AssemblyKeyFile attribute tells the compiler where to find the .SNK file that contains the developer's public key. This attribute will work with either the public/private key pair or the public-only key, something that allows developers to build, test, and debug their components without access to the organization's private key. In order to build an assembly using only a public key, you must also use the System.Reflection.AssemblyDelaySign attribute to inform the compiler that no private key is present and that no meaningful digital signature can be produced. When delay signing is used, space is reserved for the digital signature so that a trusted member of the organization can re-sign the assembly without having to replicate the original developer's build environment. In general, assemblies that have a public key but do not have a valid signature cannot be loaded or executed. To allow delay-signed assemblies to be used during development, this policy can be disabled for a particular assembly or public key using the -Vr option to SN.EXE. Figure 2.7 shows the AssemblyKeyFile attribute used from C#. This figure also shows the resultant assembly as well as another assembly that references it. Note that the 128-byte public key is stored in the target's assembly manifest along with a digital signature to protect the assembly from tampering. Also note that the second assembly, which references the target, contains only the 8-byte public key token. Because the target assembly was built with delay signing turned off, the assembly can now be deployed and loaded in secured environments. In contrast, the target assembly produced by the C# compiler shown in Figure 2.8 is not suitable for deployment because it is built with delay signing turned on. However, after a trusted individual signs the assembly with the private key, the assembly is ready to be deployed. Note that in this example, the SN.EXE tool is used with the -R option, which overwrites the digital signature in the target assembly with one based on the public/private key provided on the command line. To manually verify that an assembly has been signed, you can use SN.EXE with the -v or -vf option. The latter overrides any configured settings that might disable signature verification.

Figure 7Figure 2.7: Strong Assembly References

Figure 8Figure 2.8: Delay Signing an Assembly

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020