I've recently undertaken the task of setting up a
Public Key Infrastructure
(offline Root, online issuer) for my current engagement. I've been
through this a few times and there is a lot of info out there, so rather
than write a detailed step-by-step, I'm going to list major notes
& "gotchas" while providing links to other blogs and tech
articles.
Update note: This article was authored in April of 2012, when SHA2xx adoption by network devices was such that SHA1 was still predominant in enterprises. When instructed below to use SHA1 for the online CA, please do not. SHA256 should be considered the minimum as of 2016.
Why an offline root?
An offline root is a much more secure option than having your online issuing enterprise CA serve as root because if the root CA were to be compromised it could invalidate your entire PKI. By keeping your root CA offline (unplugged or shut down) you make it nearly impossible to compromise that box. In that scenario, if one of your online issuing CAs is compromised you will only need to revoke the certificates issued from that level down. (or just that CA depending on circumstances) This will save you from having to re-build from scratch.
More info:
Technet Wiki entry by Kurt Hudson, Ed Price and others
Prerequisites:
- Assumes there is no existing CA infrastructure. If you have one you will need to either A>Decommission or B> Transition. Follow the Decom link for more info there; the transition piece can have many variables so I won't cover that here.
- Assumes you have licenses for Windows. As of 2008, you will need at least 1 Standard edition (for the offline root) and 1 Enterprise edition. (for full functionality of the issuing CA, you can use Standard with slightly reduced functionality)
Step 1: Setup Offline CA
Setup Server
- Setup a new Windows 2008r2 Standard Edition server. If running on a virtualization platform err on the side of compatibility vs. performance when selecting virtual hardware. Make sure you record the admin password for your company since after getting the system setup it'll be quite a long time before you need to log on again.
- DO NOT JOIN THIS SERVER TO YOUR DOMAIN then fix your caps lock key. (mine was stuck)
- Enable RDP if desired. (available under 3>Customize This Server in the "Initial Configuration Tasks") The rest of this guide assumes you're connected via RDP.
- Name the server as desired, then activate and then fully update using Windows Update. Make sure the time & time zone are set correctly.
Install Certificate Services
- From Server Manager, select "Roles->Add Roles"
- On the Server Roles page, select "Active Directory Certificate Services" and hit "Next"
- Under "Role Services", select "Certification Authority" only & hit "Next".
- The "Setup Type" should default to "Standalone"; ensure the "CA Type" defaults to "Root CA".
- On the "Private Key" step, select "Create a new private key" and then we have a couple choices to make under "Cryptography"
- CSP: Generally stick with the default "RSA#Microsoft Software Key Storage Provider" unless you have need of a different CSP by way of other network hardware such as smart cards, etc. You should know if you need a different CSP. If you don't, you don't. :)
- Hash Algorithm: This can be a bit tough; SHA256 (SHA2) is a much more secure hash than SHA1, but some systems may not be able to use it. (WinXP SP2, some Oracle services) You'll need to weigh the risk here. In my scenario I'm deploying this time around for a small/mid business with significant legacy equipment, so I'll favor compatibility over security. If you're unsure, follow my lead and select the "SHA1" algorithm. If you're certain you can get away with it, (not WinXP SP3 will have enroll issues) select "SHA256" or better.
- Key character length: This is a similar discussion as the hash. If you plan on having a key duration longer than 10 years, (which I'll recommend in a moment) it is generally suggested (2 links there) to shoot for 4096 bit, but that may have compatibility and performance tradeoffs. One notorious offender has been Cisco, but their main IOS resolved that issue in ver 12.4T. That said, ensure all devices you will need certs on and select for 4096 if possible. If you are unsure on not capable of verifying, select 2048.
- "Allow administrator interaction when the private key is accessed by the CA.": Check this if your CSP (above) requires it. The default Microsoft Software KSP does NOT require it.
- For "CA Name": Set a good common name for the root CA. This should not reflect the machine name but rather the organization, i.e. "MyCompany Root CA". Keep it short and without special characters. Set the Distinguished name suffix to something that doesn't reveal security information about your internal structure. This does not need to match AD as this isn't an AD integrated system. It can be blank if desired. I'm using "OU=PKI,O=CompanyName,C=US" where US is the country code. (use yours as appropriate)
- Validity Period: 20 years. A good rule of thumb is that top level CAs must be at least twice the duration of the CA directly below it. Do 10 if you like, but I see little reason for it. See here for further considerations.
- Certificate Database: Default locations for the offline root CA. We'll change the locations for performance reasons on the issuing CA but that's not a concern here.
- Accept the rest of the dialogs and continue.
Step 2: Configure Offline CA
Change the Default Cert Request Action
First we'll ensure that certificate requests will NOT be automatically processed by the Root CA. Note: this appears to be correct by default in Win2k8r2, but due to its importance I'm leaving the step in.
- Open the cert authority and drill to Certification Authority->CA Name
- Right Click->Properties
- Policy Module->Properties
- Check the box that says "Set the certificate request status to pending."
- Click "OK" twice to get back to the main CA MMC
Set the CRL Publication Interval
The CRL defines which certificates have been revoked. You need to strike a balance between administrative overhead and time for effect on revocation. Since this CA is offline each time the CRL needs to be published it will be a manual process. The only certificate revocation that will be published by this is for a subordinate CA. For my scenario I'll be using the CRL publishing interval of 6 months.
- Expand your Root CA object and Right Click "Revoked Certificates"->Properties
- Set "CRL publication interval" to the desired time frame. I'm recommending 6 months.
- Ensure "Publish Delta CRLs" is not checked.
- Click "OK"
Set Configuration DN, Domain DN and Certificate Validity Period Registry Keys
Note: You can skip the ca\DSxxxxxxDN steps if you NEVER plan on publishing CRLs or Certs via Active Directory, but its an easy step so I don't recommend it.
When you use variables in the AIA and CDP paths for the LDAP publication (i.e.
) these registry keys are referenced to populate those fields with the correct information.
- Open a command prompt as administrator
- Execute "certutil -setreg ca\DSConfigDN CN=Configuration, DNpath" (i.e. certutil -setreg ca\DSConfigDN CN=Configuration,DC=CompanyName,DC=local)
- Execute "certutil -setreg ca\DSDomainDN DNpath"
- DNpath should be the appropriate path. To get it correct you can use ADSIEdit to connect to the default naming context.
- Execute "certutil -setreg ca\ValidityPeriodUnits 10"
- Execute "certutil -setreg ca\ValidityPeriod "Years"
- These last two commands set the default duration of certificates issued. Since we will only issue for intermediate CAs we'll set it for 10 years. If you set your RootCA for 10 rather than 20 earlier, follow your own lead and set this to 5 instead.
Set CDP and AIA Locations
The CDP and AIA locations specify the place clients can retrieve the CRL and certificate. Remember this CA is offline, so we need a maintainable future proof strategy to serve those up. For that reason, I'm recommending that the primary delivery method be http using a custom DNS name dedicated for the task. I'll then use our public web infrastructure (with
split DNS) and rely on the SLA associated with that platform. I can then use host headers to parse out the PKI requests and have everything served up on port 80. I will be using the hostname
pki.company.net. Substitute yours where appropriate. Alternatively it would be easy to use the custom DNS to point to your (not yet built) online issuing CA. Additionally we'll publish to LDAP as well. Note that the default paths will work for that since we set the registry locations, but I'll still be making some additional changes for added security. See
here,
here, and
here for more info.
Note: After the changes below you may be prompted multiple times to restart the CA service. Don't do it then; we'll restart it all when we're done here.
- Select the CA name at the root and Right Click->Properties
- Select "Extensions" and ensure "CRL Distribution Point (CDP)" is selected
- Select "C:\Windows..." and ensure only "Publish CRLs to this location" is checked
- Select "ldap:///..." and click "Remove" (IF you want added security...I'll explain why in a moment)
- Select "http://..." and click "Remove"
- Select "file://...." and click "Remove"
- Click "Add..." and type the following in "Location:" ldap:///CN=<CATruncatedName><CRLNameSuffix>,CN=01,CN=CDP,CN=Public Key Services,CN=Services,<ConfigurationContainer><CDPObjectClass> and click "OK".
- Important note: This is one place where I'm taking an extra measure of security; normally the CN=01 would be CN=(machinename), but I would prefer not to reveal the real name of the internal server in the CDP string. I'll be using a two digit incrementing integer for top level CAs and a three digit incrementing integer for CAs down the tree. Feel free to leave this to the default of machinename if you desire.
- With the new ldap:/// entry selected, ensure "Include in all CRLs. Specifies where to publish in the Active Directory when publishing manually." and "Include in the CDP extension of issued certificates" are checked
- Click "Apply"
- Click "Add..." and type the following in "Location:" http://pki.company.net/CertEnroll/<CaName><CRLNameSuffix><DeltaCRLAllowed>.crl (substitute the correct DNS name for your company)
- With the new http:// entry selected, ensure "Include in CRLs. Clients use this to find Delta CRL locations." and "Include in the CDP extension of issued certificates" are checked
- Click "Apply"
- Under "Select extension:" select "Authority Information Access (AIA)"
- If you chose to obscure the servername as listed a few points above: Select "C:\windows..." and click "Remove"
- Select "http://..." and click "Remove"
- Select "file://...." and click "Remove"
- If you chose to obscure the servername as listed a few points above: Click "Add..." and type the following in "Location:"
C:\windows\system32\certsrv\CertEnroll\01_<CaName><CertificateName>.crt
- Click "Apply"
- Click "Add..." and type the following in "Location:" http://pki.company.net/CertEnroll/01_<CaName><CertificateName>.crt Substitute
pki.company.net for you URL and if you did NOT opt to obscure the
servername replace 001 with <ServerShortName>.
- With the new http:// entry selected, ensure "Include in the AIA extension of issued certificates" is checked
- Click "OK"
- When prompted to restart certificate services, select yes.
Notes: The default LDAP location for AIA should be fine provided you did the registry entry stuff above. The default C: and http:// locations are fine if you don't want to obscure the server names. At this point, double check all your entries. If you proceed from here and find out there was a typo in any one of these entries later you will have to revoke the issuing CA cert to re-mediate the problem.
Step 3: Setup Online CA
In this part of the exercise we'll install all the online CA features on one box. Depending on your environment you may want to split some of the services across multiple machines. For scalability info, see:
here.
Note, you may want to take a quick moment at this time to review Appendix A below regarding the role of the CAPolicy.inf file.
Setup Server
- Setup a new Windows 2008r2 server. For full functionality on the issuing CA, use Enterprise edition. (Note 2012 has full functionality in standard and up) I recommend x64 for scalability reasons. If possible I'd recommend having a separate drive to house either the DB or the logs for performance reasons. (unless the drive is on the same subsystem) This server should be joined to the domain before you start installing certificate services.
- Enable RDP if desired. (available under 3>Customize
This Server in the "Initial Configuration Tasks") The rest of this guide
assumes you're connected via RDP.
- Name the server as desired, then activate and then fully update using Windows Update. Make sure the time & time zone are set correctly.
Install Certificate Services
- From Server Manager, select "Roles->Add Roles"
- On the Server Roles page, select "Active Directory Certificate Services" and hit "Next"
Note: the next step will prompt you to add additional role services required by two of the main roles. When prompted, click "Add Required Role Services" to continue.
- Under "Role Services", select "Certification Authority", "Certification Authority Web Enrollment","Online Responder" (if you plan on using OCSP, if you don't know what it is don't bother yet), and "Certificate Enrollment Policy Web Service" then click "Next".
- Change "Setup Type" to "Enterprise" and click "Next".
- Change "CA Type" to "Subordinate CA" and click "Next".
- On the "Private Key" step, select "Create a new private key" and then we have a couple choices to make under "Cryptography"
- Refer to the info above for details about CSP, Hash, and Key Character Length. For my main issuing CA, which this will be, I will be selecting options to ensure compatibility. I would advise (at the time of this writing) against using 4096 bit for the issuing CA for performance reasons.
- CSP: "RSA#Microsoft Software Key Storage Provider" (unless otherwise needed)
- Hash: "SHA1" (Unless you're brave enough for something nicer :) )
- Key Character Length: 2048
- "Allow administrator interaction when the private key is accessed by the CA.": Check this if your CSP (above) requires it. The default Microsoft Software KSP does NOT require it.
- For "CA Name": Set a good common name for the issuing CA. This should not reflect the machine name but rather the organization, i.e. "MyCompany Intermediate CA xx". (Where xx is an increment) Keep it short and without special characters. Set the Distinguished name suffix
to the same as the root CA.
- Certificate Request: Select "Save a certificate request to file and manually send it later to a parent CA:" and save it locally to send over later.
- Validity Period: 20 years. A good rule of thumb is
that top level CAs must be at least twice the duration of the CA
directly below it. Do 10 if you like, but I see little reason for it.
See here for further considerations.
- Certificate Database: Optimally the database location and database log location should be placed on a disk other than the OS disk. (different disk, not just performance) If performance is a very large consideration (i.e. very, very heavy load) you can split the DB from the DB log location as well. I'll be placing both on D:. Create folders and place the certificate database location to D:\pki\CertServ and set the Certificate database log location to D:\pki\CertLog
- Authentication Type: Select "Windows Integrated Authentication"
- Note there may be situations one may want to use other methods, i.e. allowing requests originating from the internet.
- Server Authentication Certificate: Unless you already have a certificate for this server, select "Choose and assign a certificate for SSL later"
- Web Server (IIS)->Role Services: Accept Defaults. The appropriate role services should already be selected, only add or remove if you have unique IIS needs.
- Confirmation: Save the report if you like and then click "Install"
- Results: You will get a warning about the installation being incomplete since the Sub CA certificate needs to be processed. Save the report if desired and click "Close"
Publish Root CA CRL & CRT to AD
- Fire up & login to the Root CA and then Open the Root CA Certificate Authority
- Expand the CA and right click on "Revoked Certificates"->"All Tasks"->"Publish"
- Keep "New CRL" selected and click "OK".
- Navigate to "C:\Windows\System32\certsrv\CartEnroll"
- IF you changed the AIA location above to replace the machinename with 01 as I did, rename the .crt file so that the machinename portion of the file is replace with 01. I.E. servername_mycompany root ca.crt becomes 01_mycompany root ca.crt
- Copy the .crt and .crl files to a domain controller (You will need to map a drive)
- Log onto the domain controller the files were copied to and open an elevated cmd prompt
- Navigate to where the files reside and publish the RootCA cert: certutil -dspublish -f "01_My Company Root CA.crt" RootCA
- Where: certutil is the tool, -dspublish is the action, -f creates a new container in AD, and RootCA specifies the cert is a Root CA cert. Important Note: For these certutil commands to run successfully you must be in the Enterprise Admin group.
- Publish the CRL: certutil -dspublish -f "My Company Root CA.crl"
Publish Root Cert to Clients via GPO
- May as well do this while we're still on the DC: Open Group Policy Management & Right Click Default Domain Policy->Edit
- Drill to Computer Configuration->Policies->Windows Settings->Security Settings->Trusted Root Certification Authorities
- Right Click->Import->Next
- Select the Root Certificate->Next->Keep default of "Place all certificates in the following store"->Next->Finish
- Log off DC
Publish Root CA CRL & CRT to Web
This step depends entirely on what type of web infrastructure you plan on using, so I'll skip it with only the following advice: Make sure the CRL and the CRT are available from the CDP and AIA locations you advertised earlier. If using the split DNS approach test the retrieval from internal and external clients. Make sure you allow + signs on IIS7 or higher by allowing "double escaping" in Request Filtering.
Set Sub CA CDP and AIA
If you planned a good infrastructure for your Offline CA, you can leverage that here as well.
- Log on to Sub CA
- Select the CA name and Right Click->Properties
- Hit "OK" on the Active Directory Certificate Services warning.
- Select "Extensions" and ensure "CRL Distribution Point (CDP)" is selected
- Select "C:\Windows..." and ensure "Publish CRLs to this location" and "Publish Delta CRLs to this location" are checked
- Select "ldap:///..." and click "Remove" (IF you want added security...I'll explain why in a moment)
- Select "http://..." and click "Remove"
- Select "file://...." and click "Remove"
- Click "Add..." and type the following in "Location:" ldap:///CN=<CATruncatedName><CRLNameSuffix>,CN=001,CN=CDP,CN=Public
Key
Services,CN=Services,<ConfigurationContainer><CDPObjectClass> and click "OK".
- Note: This is another place where I'm taking an extra measure of security; normally the CN=001 would be CN=(machinename),
but I would prefer not to reveal the real name of the internal server
in the CDP string. Since this is a sub CA I'm using a three digit incrementing integer. Feel free to leave this to the default of machinename if you desire.
- With the new ldap:/// entry selected, ensure "Publish CRLs to this location","Include in all CRLs. Specifies where to publish in the Active Directory when publishing manually.", "Include in CRLs. Clients use this to find Delta CRL locations","Include in the CDP extension of issued certificates", and "Publish Delta CRLs to this location" are checked
- Click "Apply"
- Click "Add..." and type the following in "Location:" http://pki.company.net/CertEnroll/<CaName><CRLNameSuffix><DeltaCRLAllowed>.crl (substitute the correct DNS name for your company)
- With the new http:// entry selected, ensure "Include in CRLs. Clients use this to find Delta CRL locations." and "Include in the CDP extension of issued certificates" are checked
- Click "Apply"
- Under "Select extension:" select "Authority Information Access (AIA)"
- If you chose to obscure the servername as listed a few points above: Select "C:\windows..." and click "Remove"
- Select "http://..." and click "Remove"
- Select "file://...." and click "Remove"
- If you chose to obscure the servername as listed a few points above: Click "Add..." and type the following in "Location:"C:\windows\system32\certsrv\CertEnroll\001_<CaName><CertificateName>.crt
- Click "Apply"
- Click "Add..." and type the following in "Location:" http://pki.company.net/CertEnroll/001_<CaName><CertificateName>.crt Substitute pki.company.net for you URL and if you did NOT opt to obscure the servername replace 001 with <ServerShortName>.
- With the new http:// entry selected, ensure "Include in the AIA extension of issued certificates" is checked
- Click "OK"
Process and Install Sub CA Certificate
- Log onto Sub CA
- Copy the previously created certificate request from the root of C:\ to the Offline CA
- Log onto the Offline CA and Open the Certificate Authority
- Right Click the Root of the CA->"All Tasks"->"Submit New Request"->Select the request you just copied over
- Click "Pending Requests"->Right Click (should be ID2)->"All Tasks"->"Issue"
- Click "Issued Certificates"->Right Click (should be ID2)->"Export Binary Data"
- Keep "Binary Certificate" selected and choose "Save binary data" & click "OK"
- Save as "cert.p7b" locally and then move it to the Sub CA
- Back on the Sub CA: Right click the root of the CA->"All Tasks"->"Install CA Certificate" & Select the p7b from the Root CA
- Start the CA with the "Play" button at the top.
- Make sure you delete the requests and generated certificates (*.req and *.p7b) from the filesystem on all servers.
- If you chose to obscure the servername as listed a few points above: You may need to manually add the CRL to AD for the first publish due to a bug; Open a CMD window as administrator and execute certutil -dspublish -f C:\windows\system32\certsrv\certenroll\CRLFileName.crl
Publish Sub CA CRL & CRT to Web
If you used the built-in web server you don't have much to worry about here, but if you, like I did, utilized your external facing web farm to leverage split DNS and that SLA, you'll need to devise a way to publish the CRL (and delta) regularly to the web farm. Since that shouldn't be part of the same domain you may need to get creative. I'm thinking about creating a dedicated service account, giving it an EFS cert, and then storing the powershell script on the server with the username/password required in there. That way only the svc acct will be able to read the script. I won't outline that now though... perhaps in a future post.
Test AIA and CDP Points With an Issued Certificate
With the first issued cert from your Sub CA, drop to a command line as administrator and execute:
certutil -verify -urlfetch certname.cer . This will display the result of checking the AIA and CDP of both the root and the Sub. If there are any problems go back and clear them up now before issuing any more certs. If there is an issue with the root you'll have to fix it and re-issue the Sub CA cert.
When you're done,
take the issuing CA Offline.
Step 4: Template Configuration, etc.
At this point you're actually done with the setup, but it's not all that functional yet. The next section is a start on getting the system to actively issue certificates. Before proceeding in these steps it is recommended that you mess around a bit to familiarize yourself with the product. The examples below are only a few of what could and should be many different certificate templates for a fully featured PKI. Please take time
to understand certificate templates before calling it completed and firing up your infrastructure.
Important Note: Throughout this next step I will make a couple references to enabling auto-enrollment security permissions on a given certificate template. While this is what we will ultimately want, I recommend that you first enable enroll only, test the template with a manual enrollment & use, and then circle back and enable auto-enrollment after you have verified proper functionality.
Make Desired Certificate Template Modifications
Before opening the floodgates for certificate auto-enrollment, you will want to modify certificate templates as desired. Cert templates control everything from cert duration to cert purpose. There are some that are installed by default, but I'd highly recommend familiarizing yourself with the concepts and making necessary changes before certificates are issued. Here are some great links to get you there:
At a minimum I would configure user and EFS templates for key archival. For more information regarding Key Recovery Agents, see
"Identify a Key Recovery Agent" at Technet. As a demonstration, let's setup Key Archival and fix up the basicEFS template:
Key Recovery Agent Setup
First, we need to select an account for the KRA:
- Create
or select a user that will act as the Key Recovery Agent. Choose wisely
and document accordingly; this acct will need be around for awhile. I
created a separate account for just this purpose.
Now, let's modify the Key Recovery Agent template:
- On the issuing CA, Right Click "Certificate Templates" and click Manage
- Right click "Key Recovery Agent" and click "Duplicate"
- Select Windows 2003. This will make the template V2... if we don't need V3 functionality don't create it.
- Under "General" change the Template Display Name to Key Recovery Agent for CompanyName; I
like to append the company name to the default name so you know on what
it is based and who it's for. Leave the Template Name as is. (it will
auto change)
- Under "Request Handling" ensure that "Allow private key to be exported" is checked. This will allow us to export the key and save it somewhere safe.
- Under "Superseded Templates" click "Add...", select "Key Recovery Agent" and click "OK".
- Under "Security" add the account you chose earlier and give it "Read" and "Enroll" rights.
- Click "OK"
- Start the CA server (Temporarily to for these tasks)
- Back on the CA, under "Certificate Templates", right click in a
blank space on the middle plane and select "New"->"Certificate
Template To Issue"
- Select your new EFS certificate template and click "OK"
- Repeat the last two steps for your new Key Recovery Agent.
- Select "Basic EFS" and press delete; click "Yes" to confirm
Now let's get a key for the KRA. The easiest way I know of to do this is as follows:
- Open an administrative Command Prompt
- Execute "runas /user:domain\kraAccount mmc" then hit Enter and type the password. Substitute the domain and kraAccount with the right account info.
- Add the certificates snap-in (personal) to the MMC and click "OK"
- Right click on "Certificates (Current User)"->"Personal"->"All Tasks"->"Request New Certificate"
- Click Next
- You should see "Active Directory Enrollment Policy" under "Configured by your administrator". Select it and click "Next".
- Select "Key Recovery Agent for MultiTech" and click "Enroll"
- After that completes, go back to your Issuing CA and look under "Pending Requests"
- Right click the pending cert and approve
- Navigate to "Issued Certificates"
- Right click the newly issued KRA cert and Right Click->"All Tasks"->"Export Binary Data"
- Select "Save binary data to a file" and save the cert (as whatever.p7b) to somewhere you can get to with the client.
- Back at the client, Right click "Personal"->"All Tasks"->"Import"
- When prompted, select your new cert and navigate through the wizard.
- After importing, select the newly imported cert (under personal->certificates) and Right Click->"All Tasks"->"Export"
- Hit "Next", "Yes, Export the Private Key", "Next", "Personal
Information Exchange...","Next", type a password, "Next", select a
location, "Next","Finish"
- Copy that key to a safe location that will be backed up.
Enable the Recovery Agent on the Issuing CA
- On the Issuing CA, right click the CA name and click "Properties"
- Hit the "Recovery Agents" tab and select "Archive the key"
- Click "Add" and hit "OK" when presented with the cert you just created.
- Click "OK"
- Restart the service when prompted.
Modify the Basic EFS Template
- On the issuing CA, Right Click "Certificate Templates" and click Manage
- Right click "Basic EFS" and click "Duplicate"
- Select Windows 2003. This will make the template V2... if we don't need V3 functionality don't create it.
- Under "General" change the Template Display Name to Basic EFS for CompanyName; I
like to append the company name to the default name so you know on what
it is based and who it's for. Leave the Template Name as is. (it will
auto change)
- Check "Do not automatically re-enroll if a duplicate certificate exists in Active Directory". Publish in Active Directory should already be checked. This
will ensure if a user already has pulled an EFS cert and stored it in
AD that the old one will be used rather than grabbing a new one.
- Under "Request Handling" check "Archive subject's encryption private key". This
will store a copy of the private key on the CA so that you can use the
key recovery agent to get it in the future if it is a problem.
- Under "Superseded Templates" click "Add...", select "Basic EFS" and click "OK". This will force people who pulled an EFS template to get a new cert with this one.
- Under "Security" check "Autoenroll" for "Domain Admins", "Enterprise Admins", and "Domain Users" and/or anyone you would want to use EFS. (Important, see the note below)
- Click "OK"
- Start the CA server (Temporarily to import cert)
- Back on the CA, under "Certificate Templates", right click in a
blank space on the middle plane and select "New"->"Certificate
Template To Issue"
- Select your new EFS certificate template and click "OK"
- Select "Basic EFS" and press delete; click "Yes" to confirm
- Stop your CA to prevent issuing more certs before you have completed your template tweaks
Note:
Unless you fully understand EFS, don't go forward without revoking the permissions to "Domain Users" on the template. If you have users who have files already encrypted with local or other PKI keys you'll need a migration strategy. It may be worthwhile to initially set the template to "enroll" rather than "autoenroll" and then use "cipher.exe /K" to gen a new key, "cipher.exe /U" to update previous files, and then "cipher.exe /x" to export the key for other machines. (remember the private key is not stored in Active Directory) For more info, see:
Zow, that was fun. So much so I'll do another one. The default
DC cert is the Windows 2000 geared "Domain Controller". If you, like I,
have all 2008 or higher DCs you can use the "Kerberos Authentication"
template. If you have mixed 2003/2008 or just 2003 use the "Domain
Controller Authentication" template.
- On the issuing CA, Right Click "Certificate Templates" and click Manage
- Right click "Kerberos Authentication" and click "Duplicate"
- Select Windows 2003. This will make the template V2... if we don't need V3 functionality don't create it.
- Under "General" change the Template Display Name to Kerberos Authentication for CompanyName; Leave the Template Name as is.
- Under "Superseded Templates" click "Add...", select "Domain Controller" and click "OK". Rinse and repeat for "Domain Controller Authentication"
- Click "OK"
- Start the CA server (Temporarily to import cert)
- Back on the CA, under "Certificate Templates", right click in a
blank space on the middle plane and select "New"->"Certificate
Template To Issue"
- Select your new Kerberos certificate template and click "OK"
- Select "Domain Controller" and press delete; click "Yes" to confirm
- Select "Domain Controller Authentication" and press delete; click "Yes" to confirm (Unless you have 2k3 DCs)
To get SSL encrypted LDAP working, follow the instructions in
this article.
Let's make one for Terminal Services & Standard Machine ID/Encryption:
Note: Let me save you some time & research and just state that you cannot automatically add the NETBIOS name as a subject alternative name with templates. If you want so suppress the certificate warnings on RDP connections you'll need to use the FQDN.
- On the issuing CA, Right Click "Certificate Templates" and click Manage
- Right click "Computer" and click "Duplicate"
- Select Windows 2003. This will make the template V2... if we don't need V3 functionality don't create it.
- Under "General" change the Template Display Name to ComputerForCompanyName; Leave the Template Name as is.
- Note: Per several articles, Microsoft dictates that: "Important: You must set the certificate template’s attributes Template display name and Template name to the same value." Because of this, I've omitted all spaces from the Computer certificate in this demonstration.
- Under "Superseded Templates" click "Add...", select "Computer" and click "OK".
- Under "Security" check "Enroll" and "Autoenroll" for any Machines you want to autoenroll. You will have to add the specific machines/groups if need be.
- Click "OK"
- Start the CA server (Temporarily to import cert)
- Back on the CA, under "Certificate Templates", right click in a
blank space on the middle plane and select "New"->"Certificate
Template To Issue"
- Select your new Computer certificate template and click "OK"
- Select "Computer" and press delete; click "Yes" to confirm
Edit GPO to Specify Certificate Template
At the desired level (be it Default Domain Policy or a policy that applies to servers only, etc.) edit the target GPO. This procedure will automatically set templates for Windows Vista and higher machines. For 2k3 & XP you'll need to open the certificates MMC and request a cert manually. Fortunately they will detect the issuing CA and process the request from template quickly.
- Navigate to "Computer Configuration"->"Administrative Templates"->"Windows Components"->"Remote Desktop Services"->"Remote Desktop Session Host"->"Security"
- Edit "Server Authentication Certificate Template"
- Enable the setting and type the template name (ComputerForCompanyName)
- Click "OK" and close the GPO Object
Configure Default Domain Policy for Auto-enrollment
- Open group policy management and edit the "Default Domain Policy"
- Navigate to "Computer Configuration"->"Windows Settings"->"Security Settings"->"Public Key Policies" and modify "Certificate Services Client - Auto-Enrollment Properties"
- Set "Configuration Model" to "Enabled" and check "Renew expired certificates..." and "Update certificates that use certificate template" and click "OK"
- Navigate to "User Configuration"->"Windows Settings"->"Security Settings"->"Public Key Policies" and modify "Certificate Services Client - Auto-Enrollment Properties"
- Set "Configuration Model" to "Enabled" and check "Renew expired certificates..." and "Update certificates that use certificate template". Enable "Expiration Notification" if you like and click "OK"
Now double check everything. If all elements look to be configured correctly feel free to start up the issuing CA and watch the requests come in.
Congrats! You have setup an enterprise class Certificate Authority, one of the most crucial security components of any enterprise infrastructure. You probably deserve a caffeinated beverage now.
Appendix A: When to use a CAPolicy.inf file
Note: See
Windows 2008r2 CAPolicy.inf syntax for implementation specifics
The %systemroot%\CAPolicy.inf file can be put into place on a target CA to further customize the creation of the certificate associated with that CA and SubCAs. If you do wish to customize the Root CA cert with any of the values listed below you'll need to do so prior to the creation of the CA cert; you can't add this stuff after the fact without re-issuing impacted certs.
In Windows 2003, it was necessary to always use a CAPolicy.inf file to ensure the root didn't have a CDP or AID associated with its cert, but that was fixed in Windows 2008. Due to this, it's no longer required to use the CAPolicy.inf file for a proper implementation, but there are some points where you may still want one. Here are the major ones:
PolicyStatementExtension: Use this to issue a legal notice, link to your use policy, or (if you need to) specify an OID. (You'll know if you do, generally applicable for external facing CAs issuing certs to third parties) Important note, if you plan on using certificate templates with issuance policies, you should take a look at
this reported issue and follow the advice there. The easiest one of his steps to implement at PKI hierarchy creation time is #2. I'll copy his logic here in case the link goes bad: (OID 2.5.29.32.0 is shared among all MS PKI deployments)
[Version]
Signature= “$Windows NT$”
[PolicyStatementExtension]
Policies = AllIssuancePolicy
Critical = FALSE
[AllIssuancePolicy]
OID = 2.5.29.32.0
CRLDistributionPoint: This is only applicable for the RootCA and shouldn't be used in most cases. Most platforms don't honor CRLs for a root CA anyhow. Doing so would question the concept of a trusted root.
AuthorityInformationAccess: Same as above; you would only have the AIA if you already have the cert, and if you already have the root cert you either do or don't trust it already.
EnhanceKeyUsageExtension: Use this to limit the usage of this CA cert (or otherwise) to specific uses. If omitted, the CA can be used to issue any type of cert. Obviously you'll leave this blank in most scenarios.
BasicConstraintsExtension: If you are relatively certain of your long term hierarchy you may want to use this on the root CA to limit how many SubCAs may fall under this root CA. If set to 1 for example it would make it impossible for a SubCA to issue a cert for a lower level SubCA. If you desire to implement this on a SubCA but not the root, configure the registry rather than using the CAPolicy.inf.
CrossCertificateDistributionPoints: Use to specify a CCDP location (URL) if your CA has been certified by a third party PKI. You may also specify the SyncDeltaTime (how often the URL is updated) here if desired. This value will only be used when you have negotiated a cross-PKI certification. Obviously you would know if you've done this. :)
RequestAttribues: Generally used on a SubCA; this allows you to change the default SubCA template that will be used. To use this value you will need to have duplicated the Sub CA template to a new name, apply the changes you desire, publish the template, and set the CertificateTemplate value to your duplicated template. The default template is version 1, so if you would like a version 2 or 3 certificate for your SubCA you'll need to use this field.
certsrv_server: Control the renewal settings for issuing CA certs. Usually not used because 1> The defaults are sufficient for most and 2> They can be changed "on the fly" (with services restart) in the registry on CAs for all certs issued thereafter. You may want to take a look at setting
LoadDefautTemplates to 0 if you want to ensure your CA doesn't issue any certs until you publish your custom templates. You will see it recommended in some places to explicitly set the renewal validity here even if you do use the defaults, but I opt not to. Though it may be spelled out directly in this text file, I'm more a proponent of handing off the "Tyranny of the Default" (thanks Steve Gibson) to anyone down the line. Generally this will ease troubleshooting because assumptions of the default are true. I.E. only change it if the default values will not work for you.
Now to address the oft-asked question "Do I need a CAPolicy file?" directly: Can you get by without a CAPolicy.inf in Windows 2008r2? Yes. Should you? Only after you review and understand its role in the process can you safely ignore it. More often than not you will want to use it to tweak a setting or two.
More references for CAPolicy.inf:
Designing and Implementing a PKI Part 2
Windows Server 2008r2 CAPolicy.inf Syntax
MS Social: CAPolicy.inf questions
CAPolicy.inf syntax
Appendix B: Publish new CRLs from Offline CA
Every six months (in our
implementation) you will need to publish the new certificate revocation
list to keep everything running smoothly. To do so:
- Fire up the offline Root CA & login as admin
- Open & expand CA object in the CA management MMC
- Right click "Revoked Certificates"->"All Tasks"->"Publish"
- Navigate to "C:\Windows\System32\certsrv\CertEnroll"
- The new CRL should be there; now you need to copy it to the appropriate path on the webserver and publish to AD. Copying to the webserver speaks for itself, AD info follows:
- Copy the file to a domain joined computer & log on to that box with Domain Admin privs
- Open a command prompt as administrator
- Execute the command: certutil -dspublish "My Company Root CA.crl"
- Done! Log off the PC and shut down the Offline CA for another six months.
Questions/Comments/Improvements please let me know. Thanks and good luck!
