LibreSSL

Key takeaways

LibreSSL belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect LibreSSL to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of LibreSSL from memory before moving on to harder problems.

Reference excerpt

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.

History 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 (Classic Mac OS, NetWare, OS/2, 16-bit Windows) and some older operating systems (OpenVMS) 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, 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 TLS 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 dropped LibreSSL after being supported since Python 3.4.3 (2015).

Adoption LibreSSL is the default provider of TLS for:

Dragonfly BSD OpenBSD Hyperbola GNU/Linux-libre OpenSSH on Windows LibreSSL was the default provider of TLS for these now-discontinued systems:

OpenELEC TrueOS packages LibreSSL is a selectable provider of TLS for:

FreeBSD packages Gentoo packages (support dropped as of February 2021) OPNsense packages (will be dropped after 22.7) macOS

Changes

Memory-related Changes include replacement of custom memory calls to ones in a standard library (for example, strlcpy, calloc, asprintf, reallocarray, etc.). 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.

Proactive measures 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, explicit_bzero and bn_clear calls were added to prevent the compiler from optimizing them out and prevent attackers from reading previously allocated memory.

Cryptographic 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).

Added features 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:

2.1.0: Automatic ephemeral EC keys. 2.1.2: Built-in arc4random implementation on macOS and FreeBSD. 2.1.2: Reworked GOST cipher suite support. 2.1.3: ALPN support. 2.1.3: Support for SHA-256 and Camellia cipher suites. 2.1.4: TLS_FALLBACK_SCSV server-side support. 2.1.4: certhash as a replacement of the c_rehash script. 2.1.4: X509_STORE_load_mem API for loading certificates from memory (enhance chroot support). 2.1.4: Experimental Windows binaries. 2.1.5: Minor update mainly for improving Windows support, first working 32- and 64-bit binaries. 2.1.6: libtls declared stable and enabled by default. 2.2.0: AIX and Cygwin support. 2.2.1: Addition of EC_curve_nid2nist and EC_curve_nist2nid from OpenSSL, initial Windows XP/2003 support. 2.2.2: Defines LIBRESSL_VERSION_NUMBER, added TLS_*methods as a replacement for the SSLv23_*method calls, cmake build support.

Old insecure features 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:

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Worked examples

Example 1 — a first encounter with LibreSSL

Start with the simplest possible case. Write down what LibreSSL claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to LibreSSL before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about LibreSSL ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of LibreSSL

In research: LibreSSL appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses LibreSSL in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: LibreSSL is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2014 software, C (programming language) libraries, Cryptographic software, so understanding it makes those chapters shorter.
In everyday life: Look for LibreSSL outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study LibreSSL in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what LibreSSL means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain LibreSSL out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is LibreSSL in simple terms?

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.

Why does LibreSSL matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study LibreSSL?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on LibreSSL.