Network Security Services

Network Security Services (NSS) is a set of libraries designed to support cross-platform development of security-enabled client and server applications. NSS supports SSL v3-TLS 1.2 (experimental TLS 1.3), PKCS #5, PKCS#7, PKCS #11, PKCS #12, S/MIME, X.509 v3 certificates, and other security standards.

Getting started

In order to get started create a new directory on that you will be uses as your local work area, and check out NSS and NSPR. (Note that there's no git mirror of NSPR and you require mercurial to get the latest NSPR source.)

git clone
hg clone

NSS can also be cloned with mercurial

hg clone

Building NSS

This build system is under development. It does not yet support all the features or platforms that NSS supports. To build on anything other than Mac or Linux please use the legacy build system as described below.

Build requirements:

After changing into the NSS directory a typical build is done as follows


Once the build is done the build output is found in the directory ../dist/Debug for debug builds and ../dist/Release for opt builds. Exported header files can be found in the include directory, library files in directory lib, and tools in directory bin. In order to run the tools, set your system environment to use the libraries of your build from the "lib" directory, e.g., using the LD_LIBRARY_PATH or DYLD_LIBRARY_PATH.

Usage: [-hcv] [-j <n>] [--nspr] [--gyp|-g] [--opt|-o] [-m32]
                [--test] [--pprof] [--scan-build[=output]] [--ct-verif]
                [--asan] [--ubsan] [--msan] [--sancov[=edge|bb|func|...]]
                [--disable-tests] [--fuzz[=tls|oss]] [--system-sqlite]
                [--no-zdefs] [--with-nspr] [--system-nspr] [--enable-libpkix]

This script builds NSS with gyp and ninja.

This build system is still under development.  It does not yet support all
the features or platforms that NSS supports.

NSS build tool options:

    -h               display this help and exit
    -c               clean before build
    -v               verbose build
    -j <n>           run at most <n> concurrent jobs
    --nspr           force a rebuild of NSPR
    --gyp|-g         force a rerun of gyp
    --opt|-o         do an opt build
    -m32             do a 32-bit build on a 64-bit system
    --test           ignore map files and export everything we have
    --fuzz           build fuzzing targets (this always enables test builds)
                     --fuzz=tls to enable TLS fuzzing mode
                     --fuzz=oss to build for OSS-Fuzz
    --pprof          build with gperftool support
    --ct-verif       build with valgrind for ct-verif
    --scan-build     run the build with scan-build (scan-build has to be in the path)
                     --scan-build=/out/path sets the output path for scan-build
    --asan           do an asan build
    --ubsan          do an ubsan build
                     --ubsan=bool,shift,... sets specific UB sanitizers
    --msan           do an msan build
    --sancov         do sanitize coverage builds
                     --sancov=func sets coverage to function level for example
    --disable-tests  don't build tests and corresponding cmdline utils
    --system-sqlite  use system sqlite
    --no-zdefs       don't set -Wl,-z,defs
    --with-nspr      don't build NSPR but use the one at the given location, e.g.
    --system-nspr    use system nspr. This requires an installation of NSPR and
                     might not work on all systems.
    --enable-libpkix make libpkix part of the build.

Building NSS (legacy build system)

After changing into the NSS directory a typical build of 32-bit NSS is done as follows:

make nss_build_all

The following environment variables might be useful:

The complete list of environment variables can be found here.

To clean the build directory run:

make nss_clean_all



Make sure that the address $HOST.$DOMSUF on your computer is available. This is necessary because NSS tests generate certificates and establish TLS connections, which requires a fully qualified domain name. You can test this by calling ping $HOST.$DOMSUF. If this is working, you're all set. If it's not, set or export:


Note that you might have to add nss.local to /etc/hosts if it's not there. The entry should look something like nss.local nss.

If you get name resolution errors, try to ensure that you are using an IPv4 address; IPv6 is the default on many systems for the loopback device which doesn't work.

Running tests

Runnning all tests will take a while!

cd tests

Make sure that all environment variables set for the build are set while running the tests as well. Test results are published in the folder ../../test_results/.

Individual tests can be run with the NSS_TESTS environment variable, e.g. NSS_TESTS=ssl_gtests ./ or by changing into the according directory and running the bash script there cd ssl_gtests && ./ The following tests are available:

cipher lowhash libpkix cert dbtests tools fips sdr crmf smime ssl ocsp merge pkits chains ec gtests ssl_gtests bogo

To make tests run faster it's recommended to set NSS_CYCLES=standard to run only the standard cycle.


NSS releases can be found at Mozilla's download server. Because NSS depends on the base library NSPR you should download the archive that combines both NSS and NSPR.


Bugzilla is used to track NSS development and bugs. File new bugs in the NSS product.

A list with good first bugs to start with are listed here.

NSS Folder Structure

The nss directory contains the following important subdirectories:

A more comprehensible overview of the NSS folder structure and API guidelines can be found here.