UPDATE (2/8): Based on some recent questions, additional information has been posted about SHA2 and Windows.
We’ve recently received a couple of requests from customers around the functionality of SHA-256 when running on Windows XP and 2003. This has been more important recently, as NIST has recommended the migration off of SHA-1 by end of the year. More details about the NIST recommendation can be found in SP 800-78-2 and SP 800-57. Hopefully this blog post can help clear up the confusion surrounding scenarios that work and the ones that don’t.
Prior to Windows XP Service Pack 3, there was no SHA2 functionality within Windows XP. With the release of Service Pack 3 some limited functionality was added to the crypto module rsaenh.dll. This includes the following SHA2 hashes: SHA-256, SHA-384, SHA-512. SHA-224 was not included.
Windows Server 2003 Service Pack 2 does not ship with support for SHA2. This limitation can become an important concern when processing smart card logons and for mutual TLS authentications to web servers. As unlike other technologies, smart card logon and mutual TLS both use strict revocation checking; so should either the certificate itself or the revocation information (CRL/OCSP) use SHA2, the logon would fail.
Though support SHA2 is not included in Windows Server 2003 Service Pack 2, it is available for download. KB 938397 will bring Windows Server 2003 to the same level of functionality as Windows XP with Service Pack 3. KB 938397 is not available via Windows Update; it needs to be requested via the “View and request hotfix downloads” link on the support page. Note, KB 938397 is also offered for Windows Server 2003 Service Pack 1.
With the release of Windows Server 2008 it was found that Windows XP Service Pack 3 and Windows Server 2003 Service Pack 2 with KB 938397 were unable to request certificates from a Windows Server 2008 (and 2008 R2) certificate authority (CA) who’s certificate was signed with a SHA2 hash. KB 968730 was release to address this issue. Incidentally, KB 968730 completely supersedes KB 938397; so if a Windows Server 2003 Service Pack 2 system would need to both enroll from a SHA2 certificate authority and process SHA2 certificates, only KB 968730 would need to be installed. As before, KB 968730 is not available via Windows Update; it needs to be requested via the “View and request hotfix downloads” link on the support page. Note, KB 968730 is not offered for Windows Server 2003 Service Pack 1.
Starting with Windows Vista and Server 2008, the Cryptography Next Generation (CNG) Suite B algorithms (including SHA2) are included in the operating system. It is worth noting that even though the algorithms are available, it is up to the individual applications to implement support.
Besides logon, another very popular use for smart cards is S/MIME. But before diving into Outlook and S/MIME, the following warning should be given: Regardless of the functionality Windows and Outlook provide; in order for mail to be delivered between two users, there are any number of spam filters, relays, mailboxes, etc between sender and recipient. Each of these can be made by a wide range of vendors; running on a wide range of platforms. So before deploying SHA2, testing should be done against one’s own email infrastructure, in addition to the email infrastructure of external organizations from whom S/MIME signed mail needs to be exchanged with.
All those warnings aside, the basic functionality for Outlook is a follows. Outlook 2003, 2007, and 2010 running on Windows XP Service Pack 3 can sign and validate certificates when that certificate itself is SHA2 signed. Outlook 2003, 2007, and 2010 running on Windows XP Service Pack 3 cannot validate email messages when the message itself is SHA2 signed (regardless of the certificate used). Outlook 2003, 2007, and 2010 running on Windows XP Service Pack 3 cannot sign a message with SHA2; only SHA-1 and MD5 are available.
In order to validate SHA2 messages, Windows Vista with Outlook 2003 (or newer) is needed. In order to both sign and validate SHA2 messages, Windows Vista or 7 with Outlook 2007 or 2010 is needed.
For organizations looking to deploy SHA2 or organizations that interact with 3rd parties that will soon begin using SHA2, the following is recommended.
XP SP3 with KB968730
2003 R2 SP2
2003 R2 SP2 with KB968730
Windows Vista, 7, 2008, 2008 R2
Browsing a website using SHA2 certificate
Unable to validate certificate
Open a certificate and viewing properties
Client with SHA2 certificate; server with SHA1 certificate
Client with SHA2 certificate; server with SHA2 certificate
Unable to login
V3 certificate template enrollment from any type of root
Unable to select template
V2 certificate template enrollment from SHA2 root
Validate and sign to a SHA2 certificate
Validate message body signed with SHA2
Sign message body with SHA2
Not an available option
Validate and sign to a SHA2 certificate using SHA-1 for the message signature