OnAugust 14, 2012, Microsoftwillissue a critical non-security update(KB 2661254) for Windows XP, Windows Server 2003, Windows Server 2003 R2, Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2. The update will block the use of cryptographic keys that are less than 1024 bits. This update was first announced in the blog titled RSA keys under 1024 bits are blocked. This blog post is a reminder that the update is coming and provides a bit more information on how to control the updatewhen deployed.

Note:The modification (opt-out settings) discussed in this article will applythroughout the operating system. You cannot configure these modifications to be applicable to a specific application, custom certificate, or scenario. You can configure thesemodificationsbefore the update is applied and when the update is applied, they will take effect. The update will require a restart.

You can modify a registry setting using the certutil command to modifythe size of the keys thatareblocked. For example, if you wanted to allow 512 bit keys, but block all keys less than 512 bits, you could run the following command:

Certutil -setreg chain\minRSAPubKeyBitLength 512

Note: All certutil commands shown in this article require local Administratorprivilegesbecause they are modifiying the registry. You can disregard the message that reads "The CertSvc service may need to be restarted for changes to take effect." That is not required for these commands as they do not affect the certificate service (CertSvc).

If only the root certificate in a chain is 512 bits, but all the rest of the keys below are 1024 bits or higher, you could run the following command to indicate that you will allow a 512 bit root certificate, but want to block all keys less than 1024 bits below the root certificate.

Certutil -setreg chain\EnableWeakSignatureFlags 2

Note: The above command also works with self-signed certificates with RSA keys less than 1024.

The certutil commands shown in this posting will not work on Windows XP, Windows Server 2003, or Windows Server 2003 R2. You will have to modify the registry directly using regedit.exe or reg command. Registry path: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\OID\EncodingType 0\CertDllCreateCertificateChainEngine\Config. The following table and figure illustrate registry the settings shown in the previous two examples:

If you have Authenticode signatures that were signed with keys less than 1024 bits prior to January 1, 2010, 12:00:00 AM UTC/GMT, they will not be blocked by default. If necessary, you can use the WeakRsaPubKeyTime setting to allow for the configuration of the date and time for which to consider older signatures valid. If you have reason to set a different date and time for the WeakRsaPubKeyTime, you can use certutil to set a different date and time. For example, if you wanted to set the date to August 29, 2010, you could use the following command:

certutil -setreg chain\WeakRsaPubKeyTime @08/29/2010

If you have a need to set a specific time, such as 6:00 PM UTC/GMT on July 4, 2011, then add the number of days and hours in the format +[dd:hh] to the command. Since 6:00 PM is 18 hours after midnight on July 4, 2011, you would run the following command:

certutil -setreg chain\WeakRsaPubKeyTime @07/04/2011+00:18

To enterWeakRsaPubKeyTimeand date on Windows XP, WindowsServer 2003, or Windows Server 2003 R2, use a REG_BINARY value for WeakRsaPubKeyTime.You canfigure out the hex value using certutil on Windows Vista, Windows Server 2008, ormore recentWindows operating system and then view the value in the registry or export the value to a REG file for viewing. The following table shows REG_BINARYhex value equivalents for WeakRsaPubKeyTime

Additional resources

Security advisory http://technet.microsoft.com/security/advisory/2661254.

KB 2661254: http://support.microsoft.com/kb/2661254

Additional blog posts:

RSA keys under 1024 bits are blocked

https://www.sysadmins.lv/retired-msft-blogs/pki/blocking-rsa-keys-less-than-1024-bits-part-3.aspx

Fabian Müller, Premier Field Engineer (PFE) in Germany, just wrote a detailed article discussinga commonly asked question:how do I determine if a smart card was usedfor logon? The article is posted on the TechNet Wiki with a link to the Script Center for your convenience. Check out the article at: http://social.technet.microsoft.com/wiki/contents/articles/11844.find-out-if-a-smart-card-was-used-for-logon.aspx

Public key based cryptographic algorithms strength is determined based on the time taken to derive the private key using brute force methods. The algorithm is deemed to be strong enough when the time required to derive private key is prohibitive enough using the computing power at disposal. The threat landscape continues to evolve. As such, we are further hardening our criteria for the RSA algorithm with key length less than 1024 bits.
To further reduce the risk of unauthorized exposure of sensitive information, Microsoft has created a software update that will be released in August 2012 for the following operating systems: Windows XP, Windows Server 2003, Windows Server 2003 R2, Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2. This update will block the use of cryptographic keys that are less than 1024 bits.
Some issues that you may encounter after applying this update may include:

• Error messages when browsing to web sites that have SSL certificates with keys that are less than 1024 bits
• Problems enrolling for certificates when a certificate request attempts to utilize a key that is less than 1024 bits
• Creating or consuming email (S/MIME) messages that utilize less than 1024 bit keys for signatures or encryption
• Installing Active X controls that were signed with less than 1024 bit signatures
• Installing applications that were signed with less than 1024 bit signatures (unless they were signed prior to January 1, 2010, which will not be blocked by default).

To prepare for this update, you should determine whether your organization is currently using keys less than 1024 bits. If it is, then you should take steps to update your cryptographic settings such that keys under 1024 bits are not in use.

• The security advisory is located at http://technet.microsoft.com/security/advisory/2661254.
• The KB article is available at http://support.microsoft.com/kb/2661254.

Certificate Chain Build Block of Keys under 1024 Bits

The Crypto API builds a certificate trust chain and validates that chain using time validity, certificate revocation, and certificate policies (such as intended purposes). Once the update is applied, during chain building there is an additional check to ensure that no certificate in the chain has key length less than 1024 bits). Chain building is done using the CertGetCertificateChain function. If a key chain building issue is encountered with such a certificate, then the errors produced are as follows:
Event 11, CAPI2

•CERT_TRUST_IS_NOT_SIGNATURE_VALID
•CERT_TRUST_HAS_WEAK_SIGNATURE

Working CSPs that Default to Allow Minimum 512 Bit Keys

There are three cryptographic service providers (CSPs) that default
to allow minimum 512 bit keys in Windows Server 2008 R2:

1. Microsoft Base Cryptographic Provider v1.0 (RSA)
2. Microsoft Base DSS and Diffie-Hellman
   Cryptographic Provider (DH)
3. Microsoft DH SChannel Cryptographic Provider
   (DH)

When working with V2 certificate templates, if you do not specify the key size, then the default CSP with default key size will be used to generate the key. If the default CSP is one of the above 3 CSPs on the client box, then the generated key will be under 1024 bits. The CA which has been updated with weak key protection will reject such request. As a result, we recommended that you do the following:

1. Configure the template to specify the cryptographic providers that you want to be utilized by selecting Requests must use on of the following
   providers.
2. Configure the Minimum key size to 1024 bit or larger.

When using certreq, ensure that you specify a 1024 bit or larger key in the INF file. For additional information, see Best Practice for Configuring Certificate Template Cryptography.

Discovering Usage of Keys under 1024 Bits in Certificate Templates

You can run the following query on your Certification Authorities (CAs) in order to discover certificate templates that are utilizing
keys under 1024 bits:

Certutil -dstemplate | findstr "[ msPKI-Minimal-Key-Size"| findstr /v "1024 2048 4096"

Note: The command should be run in each forest in your organization.

If you run this query, templates that utilize keys that are smaller than 1024 bits will be shown with their key size. The following figure illustrates that two of the built-in templates SmartcardLogon and SmartcardUser templates have default key lengths that have minimum key sizes of 512 bits. You may also discover other templates that were duplicated with minimum key sizes of less than 1024 bits.

For each template you discover that allow less than 1024 bit keys, you should determine whether it is available to issue certificates as shown in the Certificate Templates section of the Certification Authority console.

For these templates, you should consider increasing the Minimum key size to a setting of at least 1024 (assuming the devices to which these certificates are to be issued support a larger key size).

You should use Reenroll All Certificate Holders to cause the client computers to reenroll and request a larger key size (assuming certificate autoenrollment is enabled).

If you have issued certificates using the built-in Smartcard Logon or Smartcard User templates, you will not be able to adjust the minimum key size of the template directly. Instead, you will have to duplicate the template, increase the key size on the duplicated template, and then supersede the original template with the duplicated template.

After you have superseded the template, you should use Reenroll All Certificate Holders to cause the client computers to reenroll and request a larger key size.

Discovering usage of RSA keys under 1024 Bits in Cryptographic Operations

You can utilize CAPI2 logging starting with Windows Vista or Windows Server 2008 computers to help identify keys under 1024 bits. You can then allow the computers to perform their normal operations and check the log after a period of time to help identify such keys. You can then use that information to track down the sources of the certificates and make the necessary updates.

To accomplish this, you must first enable verbose diagnostic logging. To enable verbose mode logging:

1. Open the Registry Editor (regedit.exe).
2. Navigate to the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\crypt32
3. Add a DWORD (32-bit) value DiagLevel with value of0x00000005
4. Add a QWORD (64-bit) value DiagMatchAnyMask with value of 0x00ffffff

Once you do this, you can then enable CAPI2 operational logging in the Event Viewer. The CAPI2 Operational log is located under Applications and Service Logs, Microsoft, Windows, and CAPI2 in the Event Viewer. To enable logging, right-click the Operational log and select Enable Log.

Once you've collected the log, you can use the following filter to reduce the number of entries that you have to search through in order to find certificate operations with keys under 1024 bits. The following filter looks for keys of 512 bits.

<QueryList>

<Query Id="0"
Path="Microsoft-Windows-CAPI2/Operational">

<Select Path="Microsoft-Windows-CAPI2/Operational">Event[UserData[CertGetCertificateChain[CertificateChain[ChainElement[PublicKeyAlgorithm[@publicKeyLength='512']]]]] and
UserData[CertGetCertificateChain[CertificateChain[ChainElement[PublicKeyAlgorithm[@publicKeyName='RSA']]]]]]</Select>

</Query>

</QueryList>

You can also query multiple key lengths with a single query. For example, the following filter queries for both 384 bit and 512 bit keys.

<QueryList>

<Query Id="0"
Path="Microsoft-Windows-CAPI2/Operational">

<Select Path="Microsoft-Windows-CAPI2/Operational">Event[UserData[CertGetCertificateChain[CertificateChain[ChainElement[PublicKeyAlgorithm[@publicKeyLength='384']]]]] and
UserData[CertGetCertificateChain[CertificateChain[ChainElement[PublicKeyAlgorithm[@publicKeyName='RSA']]]]]]
or
Event[UserData[CertGetCertificateChain[CertificateChain[ChainElement[PublicKeyAlgorithm[@publicKeyLength='512']]]]] and
UserData[CertGetCertificateChain[CertificateChain[ChainElement[PublicKeyAlgorithm[@publicKeyName='RSA']]]]]]</Select>

</Query>

</QueryList>

Discovering issued RSA certificates with keys less than 1024 bits

Ingolfur Arnar Stangeland came up with a certutil command to show whether a CA has issued RSA certificates with keys less than 1024 bits. He published the instructions in his blog post "How to identify if your ADCS has issued any certificates with public keys <1024 bits (in preparation for KB2661254)" http://blogs.technet.com/b/instan/archive/2012/08/03/how-to-identify-if-your-adcs-has-issued-any-certificates-with-public-keys-lt-1024-bits-in-preparation-for-kb2661254.aspx

Additional resources

Security advisoryhttp://technet.microsoft.com/security/advisory/2661254.

KB 2661254: http://support.microsoft.com/kb/2661254

Additional blog posts:

https://www.sysadmins.lv/retired-msft-blogs/pki/blocking-rsa-keys-less-than-1024-bits-part-2.aspx

https://www.sysadmins.lv/retired-msft-blogs/pki/blocking-rsa-keys-less-than-1024-bits-part-3.aspx

There are a number of known untrusted certificates and compromised keys that have been issued by standard trusted root certification authorities. To help customers avoid interacting with these untrusted or compromised certificates and keys, an Automatic Updater of revoked certificates is now available for Windows Vista Service Pack 2, Windows Server 2008 Service Pack 2, Windows 7, and Windows Server 2008 R2 computers. Learn more and download the updater through Microsoft KB 2677070.

In the past, customers would have had to make changes to the Untrusted Certificate Store by initiating updates through Windows Update or by using a manual method. For example, the updates published in KB 2718704, which describes an update to move unauthorized certificates to the untrusted store, had to be initiated manually. This new feature provides dynamic updates for revocation information so that Windows clients can be updated with untrusted certificates at most within a day of the information being published (no user interaction required). This new automatic updaterwill enable Certificate Authorities to report information about their revoked CA certificates to Microsoft and have them publicly untrusted in a much faster manner as compared to propagating this information by using CRLs.

During my work with a customer renewing their Issuing CA’s certificate based on the steps documented in this article, I discovered that the Request file generated couldn’t be located in the default location of %systemDrive% . The Issuing CA didn’t log any errors in the Event Log, nor did it post any error messages. I also searched for all files with the extension *.req on all drives, and still couldn’t find the file.

After some more research, I discovered that my customer changed the default location of the RequestFileName Registry Key during their installation to a drive that no longer exists on the CA. The location configured was a:\%1_%3%4.req. I followed these steps to fix this issue:

1. Start the Registry Editor
2. Navigate to HKLM\System\CurrentControlSet\Services\Certsvc\Configuration\<CASanitizedName>
3. Locate the Registry String RequestFileName
4. Change the value from a:\%1_%3%4.req to C:\%1_%3%4.req
5. Stop and Start the Certification Active Directory Certificate Services service

I was then able to create the Request File and submit it to the Offline Root CA to process it.