Security Module in SUSE Linux Enterprise 11

As the name indicates, SUSE Linux Enterprise is intended for use by enterprises. One of the main attributes valued by enterprises in software is stability. SUSE achieves this in a number of ways, one of which is to not change versions of its software packages unless there is no other alternative. When SUSE Linux Enterprise 11 became generally available in 2009, OpenSSL 0.9.8 was the package included to provide encryption for the various other software that used it.

It was when the requirement for TLS 1.2 came along that a conflict arose between that need and the goal of maintaining the same software versions, and hence stability. OpenSSL version 0.9.8 simply did not provide an implementation of TLS 1.1 or 1.2 and never would provide it.

In order to provide TLS 1.2 with OpenSSL, SUSE would have to provide version 1.0 or higher. Such an update to a more recent OpenSSL version would have been nearly impossible, as OpenSSL is notoriously incompatible with itself when moving between versions. An OpenSSL version upgrade would trigger a rebuild of a significant number of other packages in SUSE Linux Enterprise 11. Subsequently this would require a high number of updates to be installed on all our customers' production systems. Worse, a version upgrade would break third party applications. This was considered unacceptable, so another approach was taken.

Fortunately, there are cryptographic libraries other than OpenSSL. Amongst those it was decided that Mozilla's Network Security Services (NSS) would be the best option:

In late November of 2013, SUSE shipped updated versions of libfreebl3, libsoftokn3, mozilla-nspr, and mozilla-nss, along with a new package apache2-mod_nss in the maintenance channels for SUSE Linux Enterprise 11 Service Pack (SP) 2 and SP3. While this took care of the Web server and Web browser cases, it did not do the same for other network services such as e-mail or tools such as wget and curl.

The e-mail server that is included with SUSE Linux Enterprise, Postfix, does not work with NSS, only with OpenSSL. Simply shipping both OpenSSL 0.9.8 and OpenSSL 1.0 was not an option because it was all too likely that customers would install both versions of OpenSSL on their systems. Because of the incompatibilities discussed earlier, this would almost certainly have led to all sorts of application crashes.

The lack of SUSE provided packages built against OpenSSL 1.0 lead to some customers attempting to recompile them from source, with mixed success. Worse, the recompiled packages were not supported by SUSE and could affect the supportability for the entire system. Further, customers would need some way of rebuilding their in-house written applications against OpenSSL 1.0 to be compliant. Clearly something more was needed.

In August of 2014, SUSE released the “SUSE Linux Enterprise 11 Security Module”, providing enhancements to SUSE Linux Enterprise 11 SP3, and later SP4. Available to all customers with a SUSE Linux Enterprise Server subscription, this allows customers and partners to build TLS 1.2 compliant infrastructures beyond the HTTPS protocol. The packages in the Security Module will be supported in the same way and for the same period of time as the other packages shipped with SUSE Linux Enterprise 11 (see https://www.suse.com/lifecycle/).

In this context the term “module” can be somewhat confusing but it comes from the “optional modules” that were introduced with SUSE Linux Enterprise 12 (see https://www.suse.com/products/server/features/modules.html). Essentially the Security Module is an additional package and maintenance repository for use by YaST or Zypper. There are no DVDs to order or ISO images to download. At this time, there are a total of 31 packages available in the Security Module:

As you can see there are packages containing executables, runtime libraries, and development files. They are also named to be easily distinguishable from the versions built against OpenSSL 0.9.8. With a few exceptions, the OpenSSL 1.0 packages may be installed concurrently with the versions using OpenSSL 0.9.8. Those exceptions that may not be installed concurrently are:

For the OpenSSH and Postfix packages, it does not make sense to have more than one version installed since they provide a service for the entire system, not just for one user or application. For the Perl and -devel packages a conflict is unavoidable as the header and .so files are in the same locations. This means that only the OpenSSL 0.9.8 or the OpenSSL 1.0 version of these packages may be installed on a given system at one time.

Since all the packages reside in a single repository or maintenance channel, there are just two major steps that need to be taken first:

Note: No Automatic Change to OpenSSL 1

Note that adding this channel or installing the SUSE provided packages does not automatically change any other existing applications to use OpenSSL 1. Unless ported or rebuilt by the vendor they will still use the OpenSSL 0.9.8 libraries. For C or C++ applications developed in-house you will need to build OpenSSL 1 versions as described in the section on how to use the development packages.

More information about the Security Module and its background can be found here:

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