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Certification Authority Root Signing

This article provides descriptional information about enterprise Certification Authority signing by commercial Certification Authority (sometimes, external root is referred as "common root").

What is Certification Authority Root Signing?

Consider the following scenario: You work for an organization that requires many digital certificates. You want to ensure that these certificates are trusted by other organizations, such as external partners and customers. For example, you might want to use a code signing certificate for an application or a digital signature certificate for signing a document or email.

If you setup your own public key infrastructure (PKI), also known as a private PKI, the certificates you issue will only be trusted internally. For example, you can publish the root certification authority certificate into your Active Directory Domain Service (AD DS) and quickly have your organization's computers trusting certificates issued by your PKI. However, external organizations, such as your customers and partners, would not (by default) trust the certificates issued by your PKI. This means they would see a validity or trust error messages, if they viewed or tried to validate a certificate issued by your PKI.

If instead, you subordinate your PKI to one of the commercial PKI root certificates that are trusted by Microsoft Windows installations, you do not have the same problem. By default, Microsoft Windows applications install a set of predefined root CA certificates (well known commercial root CAs), which certificates are trusted on any Windows installation by default. For example, if you access https://login.live.com/ web site, no additional actions are required from a user. This is because SSL certificate is issued by a trusted CA.

Contrarily, if a remote user tries to access a web site that utilizes SSL certificate from a private PKI, the user receives an error message indicating certificate trust issues. When a user application (like Internet Explorer) does not specifically trust a PKI, an error message is presented each time that private PKI's certificate is presented to the user.

To overcome such an issue, you may decide to implement a PKI that utilizes the trust of a well-known and trusted PKI. This allows your organization to issue certificates that can be trusted and recognized worldwide.


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X.509 Name Constraints certificate extension – all you should know

Hello S-1-1-0, PowerShell CryptoGuy (aka @Crypt32) is here again. Today I want to discuss about X.509 Name Constraints certificate extension. It is not widely used, but sometimes it is necessary. As extension name depicts, it is used to provide constraints or restrictions to certificate subject and subject alternative names (SAN) extension.

Brief Description

Name Constraints extension is defined and described in RFC 5280 §4.2.1.10. Extension presence in an end-entity certificate does not have any effect and is applied only to CA certificates that issue certificates to end entities. Once defined, the extension applies restrictions on any certificates that appear below that CA in the tree. Name Constraints may appear further in the certification path to set more restrictive constraints. It is not possible to set less restrictive constraints at lower levels. This prevents low-level (in the certification path meaning) CAs to violate restrictions applied at higher levels.

PKI Hierarchy

Figure 1 - sample certificate chain

Here we see a 3-tier PKI hierarchy with applied Name Constraints extension at 2nd level (below root). This is indicated by a yellow triangle. Name Constraints restrictions are applied to all directly and indirectly issued certificates. CA-2 doesn’t define Name Constraints extension in its own certificate, but restrictions still apply to certificates issued by CA-2 indirectly.


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How to read ADCS Enrollment Agent/Certificate Manager rights in PowerShell

Recently I was asked about how to read Enrollment Agent Rights and Certificate Manager Restrictions in ADCS. At first, I would like to make a little introduction about the subject.

Enrollment Agents

With Active Directory Certificate Services (ADCS) you can designate one or more enrollment agents to enroll on behalf of other users. One of the most common scenarios is smart card provisioning. Suppose, you purchased smart cards and plan to issue them to employees. You will designate one or more highly trusted persons who will:

  • instruct employees about smart card usage policies;
  • register smart card serial number/other data in the accounting system (some certificate lifecycle management system);
  • prepare smart card for use (print labels and so on);
  • install certificate for another employee.

Enrollment Agent Restrictions cover the last point in the list. Restrictions define three major parts:


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SHA1 to SHA2 transition: do it properly!

About the problem

Almost everyday we hear about SHA1 deprecation policy. Many commercial CAs now sign end-entity certificates with SHA2 (actually, SHA256) and. Some of them upgrade issuing CAs to SHA2. Many security administrators  move their private CAs and certificates to SHA2 signatures. Unfortunately, not all do this migration correctly. Companies just configure their CAs to sign certificates with SHA256. Is this enough? Actually, not.


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SSL key exchange with and without encryption

Recently, a friend of mine asked a question about key exchange in SSL without encrypting the key. His question came after examining a Key Usage certificate extension setting in the certificate template. There are two options: Allow key exchange only with key encryption and Allow key exchange without key encryption. How it can be possible that the key is not encrypted??? Here is an image of the respective setting:

Key Usage extension configuration in certificate template


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