|Original author(s)||The OpenSSL Project|
|Developer(s)||The OpenBSD Project|
|Initial release||2.0.0 / 11 July 2014|
3.5.3 / 18 May 2022
|Written in||C, assembly, Perl|
|Operating system||OpenBSD, FreeBSD, NetBSD, Linux, HP-UX, Solaris, macOS, Windows and others|
|License||Apache License 1.0, 4-clause BSD license, ISC license, public domain|
LibreSSL is an open-source implementation of the Transport Layer Security (TLS) protocol. The implementation is named after Secure Sockets Layer (SSL), the deprecated predecessor of TLS, for which support was removed in release 2.3.0. The OpenBSD project forked LibreSSL from OpenSSL 1.0.1g in April 2014 as a response to the Heartbleed security vulnerability, with the goals of modernizing the codebase, improving security, and applying development best practices.
After the Heartbleed security vulnerability was discovered in OpenSSL, the OpenBSD team audited the codebase and decided it was necessary to fork OpenSSL to remove dangerous code. The libressl.org domain was registered on 11 April 2014; the project announced the name on 22 April 2014. In the first week of development, more than 90,000 lines of C code were removed. Unused code was removed, and support for obsolete operating systems was removed.
LibreSSL was initially developed as an intended replacement for OpenSSL in OpenBSD 5.6, and was ported to other platforms once a stripped-down version of the library was stable. As of April 2014[update], the project was seeking a "stable commitment" of external funding. On 17 May 2014, Bob Beck presented "LibreSSL: The First 30 Days, and What The Future Holds" during the 2014 BSDCan conference, in which he described the progress made in the first month. On 5 June 2014, several OpenSSL bugs became public. While several projects were notified in advance, LibreSSL was not; Theo de Raadt accused the OpenSSL developers of intentionally withholding this information from OpenBSD and LibreSSL.
On 20 June 2014, Google created another fork of OpenSSL called BoringSSL, and promised to exchange fixes with LibreSSL. Google has already relicensed some of its contributions under the ISC license, as it was requested by the LibreSSL developers. On 21 June 2014, Theo de Raadt welcomed BoringSSL and outlined the plans for LibreSSL-portable. Starting on 8 July, code porting for macOS and Solaris began, while the initial porting to Linux began on 20 June.
As of 2021, OpenBSD uses LibreSSL as the primary SSL library. Alpine Linux supported LibreSSL as its primary TLS library for three years, until release 3.9.0 in January 2019. Gentoo supported LibreSSL until February 2021. Python 3.10 drops LibreSSL support after being supported since Python 3.4.3 (2015).
LibreSSL is the default provider of TLS for:
LibreSSL is the default provider of TLS for these now-discontinued systems:
LibreSSL is a selectable provider of TLS for:
Changes include replacement of custom memory calls to ones in a standard library (for example,
reallocarray, etc.).[self-published source?] This process may help later on to catch buffer overflow errors with more advanced memory analysis tools or by observing program crashes (via ASLR, use of the NX bit, stack canaries, etc.).
Fixes for potential double free scenarios have also been cited in the VCS commit logs (including explicit assignments of null pointer values). There have been extra sanity checks also cited in the commit logs related to ensuring length arguments, unsigned-to-signed variable assignments, pointer values, and method returns.
In order to maintain good programming practice, a number of compiler options and flags designed for safety have been enabled by default to help in spotting potential issues so they can be fixed earlier (-Wall, -Werror, -Wextra, -Wuninitialized). There have also been code readability updates which help future contributors in verifying program correctness (KNF, white-space, line-wrapping, etc.). Modification or removal of unneeded method wrappers and macros also help with code readability and auditing (Error and I/O abstraction library references).
Changes were made to ensure that LibreSSL will be year 2038 compatible along with maintaining portability for other similar platforms. In addition,
bn_clear calls were added to prevent the compiler from optimizing them out and prevent attackers from reading previously allocated memory.
There were changes to help ensure proper seeding of random number generator-based methods via replacements of insecure seeding practices (taking advantage of features offered by the kernel itself natively). In terms of notable additions made, OpenBSD has added support for newer and more reputable algorithms (ChaCha stream cipher and Poly1305 message authentication code) along with a safer set of elliptic curves (brainpool curves from RFC 5639, up to 512 bits in strength).
The initial release of LibreSSL added a number of features: the ChaCha and Poly1305 algorithm, the Brainpool and ANSSI elliptic curves, and the AES-GCM and ChaCha20-Poly1305 AEAD modes.
Later versions added the following:
The initial release of LibreSSL disabled a number of features by default. Some of the code for these features was later removed, including Kerberos, US-Export ciphers, TLS compression, DTLS heartbeat, SSL v2 and SSL v3.
Later versions disabled more features:
The initial release of LibreSSL has removed a number of features that were deemed insecure, unnecessary or deprecated as part of OpenBSD 5.6.
The Dual EC DRBG algorithm, which is suspected of having a back door, was cut along with support for the FIPS 140-2 standard that required it. Unused protocols and insecure algorithms have also been removed, including the support for FIPS 140-2, MD4/MD5 J-PAKE, and SRP.
One of the complaints of OpenSSL was the number of open bugs reported in the bug tracker that had gone unfixed for years. Older bugs are now being fixed in LibreSSL.