zxing qr code generator sample c# Lesson 4 in C#

Draw QR Code in C# Lesson 4

Lesson 4
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Designing the Renewal, Revocation, and Auditing Processes
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of a certificate has a valid CRL in its local cache, it does not attempt to retrieve another CRL from the CA. This means that even though a new CRL is published, it won t be retrieved until the current CRL validity period expires.
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Design the location of CRL publication points.
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By default, an enterprise CRL is published in the Active Directory and to the Web-enrollment pages. Additional or different publication points need to be established before cer tificates are issued, as the CRL publication point must be part of the certifi cate. (Certificate verifiers use the publication point on the certificate to access a CRL if necessary.) Consider the size of the implementation and the geographic dispersion to determine whether additional points are necessary. CRLs can be published to file locations, URLs, and LDAP directories. Special consideration should be taken for offline root CAs. Their CRL publi cation points must be established on the network, and automatic publication must be turned off because the offline CA cannot publish to the network. A manual process must be established for periodic publication of the CRL. A long publication period should be established so that the manual publication and manual placement of the CRL on the network will be an infrequent chore. This approach is perfectly acceptable because it would be rare to revoke the root CA certificate.
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Consider normal CRL processing by the certificate verifiers. Because they do not access a new CRL until the currently cached CRL expires, if it becomes necessary to revoke a certificate and a long publication period is established, the time needed for news of the CA revocation to reach certificate verifiers will be longer. The effect of this delay can be tempered by ensuring that the procedure for revok ing a CA certificate includes the revocation of its entire certificate list first and a delay in revoking the CA certificate until all certificate verifiers have downloaded the new CRL.
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Revocation Checking on the Internet
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Checking the revocation status of certificates on the Internet is considered to be problematic. The following items partially explain the problem:
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Older versions of Internet Explorer do not turn on revocation checking by default. Some versions of Netscape browsers cannot automatically check for revoca tion status.
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2
Designing the Logical Infrastructure
Given the size of the Internet and the erratic availability of some sites and some connections, it might not be possible to locate a CRL when necessary. Not all certificates can be issued with the location of their CDP in the certif icate. Microsoft applications as well as others look for the CDP information in the certificate in order to find the CRL. If no CDP is present, the CRL cannot be located.
Considerations for Designing the Auditing Process
After you design the revocation process, you can design the auditing process. As you design the auditing process, think about the following things:
Consider the configuration of auditing.
Auditing of CA activity requires configuration in the Certification Authority console, but it is dependent on the establishment of object access auditing in the Windows Settings, Security Settings, Local Policies, Audit policy of the appropriate Group Policy Object (GPO). If object access auditing is not turned on, specific CA activity will not be recorded in the Security event log. If the CA exists on a member server, the Audit policy should be set using Group Policy. The GPO should be linked to the domain or organizational unit (OU) that the CA computer is a member of. (The design of Group Policy is discussed in 5 and 8.)
Consider the events that can be audited. These are configured from the CA audit properties page as shown in Figure 2-17.
Figure 2-17 Selecting CA audit events to monitor
Lesson 4
Designing the Renewal, Revocation, and Auditing Processes
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Back Up And Restore Of The CA Database. Auditing these events provides a solid record of backup. Checking for successful backup is always a sound activity. In addition, an unexpected restore of the CA database located by the audit might be an indication of tampering and should be investigated. Change CA Configuration. Auditing these events allows for the tracking of successful and unsuccessful changes to configuration against planned and approved changes and provides a record of proper maintenance. Possible tampering can also be confirmed. Configuration events audited include add ing and removing templates, configuration of the CRL publication schedule, configuration of the CDPs and AIAs, changes to policy modules, and key archival and recovery. Change CA Security Settings. These events include the configuration of CA roles for role-based administration, setting of restrictions on Certificate Managers, and the configuration of auditing. It s important to note that these configuration events are not recorded by turning on the Changes In Configuration settings you must turn on Changes In CA Security Settings Auditing. Issue And Manage Certificate Requests. Auditing these events will record suc cessful and failed attempts at issuance of certificates and their management. A record can be produced for each certificate requested, issued, or imported. Revoke Certificates And Publish CRL. Auditing these events will record suc cessful and failed attempts to revoke certificates and publish CRLs. Store And Retrieve Archived Keys. If key archival is configured, auditing these events will record successful or failed attempts at storage and retrieval. Access to archived keys should be performed only according to strict policy to ensure that only authorized administrators retrieve the keys and that they are returned to the correct owner. There are technical controls to ensure this; however, checking the audit of the process against documented approved need will enable discovery of unauthorized attempts and compromised keys. Start And Stop Certificate Services. Stopping and starting certificate services is necessary to accomplish some configuration and policy changes, as well as CA key renewal. The actual events should always be audited against approved maintenance. To decide which events to audit, determine how much knowledge is needed. The amassing of large volumes of records that might never be examined is counterproductive. The policy, and therefore the design, of the audit should keep these things in mind. One way to make a determination is to examine the impact of auditing each event and make decisions based on impact vs. value.
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