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libtls - Man Page

libtls for OpenSSL


LibreTLS is a port of libtls from LibreSSL to OpenSSL. libtls is “a new TLS library, designed to make it easier to write foolproof applications”.

libtls provides an excellent new API, but LibreSSL can be difficult to install on systems which already use OpenSSL. LibreTLS aims to make the libtls API more easily and widely available.


LibreTLS is based on LibreSSL-portable sources. LibreTLS releases track LibreSSL releases, starting with version 3.2.0. If patches must be released between LibreSSL releases, the letter ‘p’ followed by an increasing digit starting from 1 will be added to the version number.

LibreTLS release tarballs are available from https://causal.agency/libretls/.


The libtls provided by LibreTLS is ABI-compatible with the libtls provided by the corresponding LibreSSL release.

The behaviour of LibreTLS and LibreSSL differs in how the root certificates are loaded by default. LibreSSL uses a hardcoded path to a CA bundle file, while LibreTLS uses the default CA locations of OpenSSL, which may include a CA directory. To restore the behaviour of LibreSSL, call tls_config_set_ca_file(3) with the path returned by tls_default_ca_cert_file(3). All other behaviour should be identical.

LibreTLS targets the OpenSSL 1.1.1 series. Due to a bug in OpenSSL, only versions 1.1.1b and newer are known to work. LibreTLS is compatible with OpenSSL 3.0.0 but hasn't been ported away from deprecated APIs.

Platform Support

LibreTLS should work on the same platforms as LibreSSL-portable, though it has not been thoroughly tested on platforms other than Linux, FreeBSD and macOS.


libtls consists of all new code developed as part of OpenBSD under OpenBSD's preferred license of ISC. Some compat sources are under the 3-clause BSD license or the MIT license.

LibreTLS is not encumbered by the dual-licensing of OpenSSL under both the OpenSSL license and the original SSLeay license, which are incompatible with the GNU General Public License. When OpenSSL 3.0 is released under the Apache 2.0 license, software under the GPLv3 will be able to link against LibreTLS and OpenSSL without additional permissions.


To install from a release tarball, run the following:

make all
make install

To install from a git checkout, autoconf, automake and libtool are required. Run the following before continuing with the steps above:

autoreconf -fi


LibreTLS is maintained by June McEnroe <june@causal.agency>.

LibreSSL is developed by The OpenBSD project.


February 27, 2022