OpenSSL 1.0.2 LTS

released: 2015-02 end of lifetime: 2019-12

OpenSSL 1.0.2 added hostname verification, ALPN support, and elliptic curves.

• CentOS 7 (EOL 2024-06)
• Debian 8 Jessie (EOL 2020-07)
• Linux Mint 18.3 (EOL 2021-04)
• RHEL 7 (full support ends 2019-08, maintenance 2 support ends 2024-06)
• SUSE Enterprise Linux 12-SP5 (general supports ends 2024-10)
• Ubuntu 16.04 LTS / Xenial (general support ends 2021-04)

OpenSSL 1.1.0

released: 2016-08 end of lifetime: 2019-09

OpenSSL 1.1.0 removed or disabled insecure ciphers by default and added support for ChaCha20-Poly1305, BLAKE2 (basic features), X25519 and CT. The majority of structs were made opaque and new APIs were introduced. OpenSSL 1.1.0 is not API compatible with 1.0.2.

• Debian 9 Stretch (security support ended 2020-07, LTS until 2022-06)
• Ubuntu 18.04 LTS / Bionic (general support ends 2023-04)

OpenSSL 1.1.1 LTS

released: 2018-08 end of lifetime: 2023-09 (planned)

OpenSSL 1.1.1 added TLS 1.3, SHA-3, X448 and Ed448.

• Alpine (switched back to OpenSSL in 2018 [4])
• Arch Linux current
• CentOS 8.0+
• Debian 10 Buster
• Debian 11 Bullseye (ETA 2021-06)
• Fedora 29+
• FreeBSD 11.3+
• Gentoo Linux stable (dropped LibreSSL as alternative in January 2021 [10])
• HardenedBSD (switched back to OpenSSL in 2018 [3])
• Linux Mint 19.3+
• macOS (python.org installer)
• NetBSD 8.2+
• openSUSE 15.2+
• RHEL 8.0+
• Slackware current
• SUSE Enterprise Linux 15-SP2
• Ubuntu 18.10+
• Ubuntu 20.04 LTS / Focal
• VoidLinux (switched back to OpenSSL in March 2021 [5])
• Windows (python.org installer, Conda)

Major CI providers provide images with OpenSSL 1.1.1.

• AppVeyor (with image Ubuntu2004)
• CircleCI (with recent cimg/base:stable or cimg/base:stable-20.04)
• GitHub Actions (with runs-on: ubuntu-20.04)
• Giblab CI (with Debian Stretch, Ubuntu Focal, CentOS 8, RHEL 8, or Fedora runner)
• Packit
• TravisCI (with dist: focal)
• Zuul

OpenSSL 3.0.0

released: n/a (planned for mid/late 2021)

OpenSSL 3.0.0 is currently under development. Major changes include relicensing to Apache License 2.0 and a new API for cryptographic algorithms providers. Most changes are internal refactorings and don’t affect public APIs. [8]

LibreSSL

created: 2014-04 (forked from OpenSSL 1.0.1g)

• DragonFly BSD
• Hyperbola GNU/Linux-libre
• OpenBSD
• OpenELEC (discontinued)
• TrueOS (discontinued)

Some distributions like FreeBSD and OPNsense also feature LibreSSL instead of OpenSSL as non-standard TLS libraries. Gentoo discontinued LibreSSL as an alternative to OpenSSL in January 2021 [10] due to compatibility issues and little testing.

OpenBSD ports has a port security/openssl/1.1 which is documented as “[…] is present to provide support for applications which cannot be made compatible with LibReSSL” [7]. The package could be used by OpenBSD to provide a working ssl module.

BoringSSL

created: 2014-06

BoringSSL is Google’s fork of OpenSSL. It’s not intended for general use and therefore not supported by Python. There are no guarantees of API or ABI stability. Vendored copies of BoringSSL are used in Chrome/Chromium browser, Android, and on Apple platforms [6].

TLS 1.3

OpenSSL 1.1.1 introduced support for the new TLS 1.3 version. The latest version of the TLS protocol has a faster handshake and is more secure than the previous versions.

Thread and fork safety

Starting with release 1.1.0c, OpenSSL is fully fork and thread safe. Bindings no longer need any workarounds or additional callbacks to support multithreading.

SHA-3

Since 1.1.0, OpenSSL ships with SHA-3 and SHAKE implementations. Python’s builtin SHA-3 support is based on the reference implementation. The internal _sha3 code is fairly large and the resulting shared library close to 0.5 MB. Python could drop the builtin implementation and rely on OpenSSL’s libcrypto instead.

So far LibreSSL upstream development has refused to add SHA-3 support. [2]

OpenSSL downstream patches and options

OpenSSL features more than 70 configure and build time options in the form of OPENSSL_NO_* macros. Around 60 options affect the presence of features like cryptographic algorithms and TLS versions. Some distributions apply patches to alter settings. Furthermore, default values for settings like security level, ciphers, TLS version range, and signature algorithms can be set in OpenSSL config file.

The Python core team lacks resources to test all possible combinations. This PEP proposes that Python only supports OpenSSL builds that have standard features enabled. Vendors shall disable deprecated or insecure algorithms and TLS versions with build time options like OPENSSL_NO_TLS1_1_METHOD or OpenSSL config options like MinProtocol = TLSv1.2.

Python assumes that OpenSSL is built with

• hashlib’s default algorithms such as MD5, SHA-1, SHA-2 family, SHA-3/SHAKE family, BLAKE2
• TLS 1.2 and TLS 1.3 protocols
• current key agreement, signature, and encryption algorithms for TLS 1.2 and 1.3 (ECDH, RSA, ECDSA, Curve25519, AES, Poly1309-ChaCha20, …)
• threading, file I/O, socket I/O, and error messages

Weak algorithms (MD5, SHA-1 signatures) and short keys (RSA < 2024 bits) may be disabled at runtime. Algorithms may also be blocked when they are disabled by a crypto policy such as FIPS. The PEP is not more specific on purpose to give room for new features as well as countermeasures against vulnerabilities. As a rule of thumb, Python should be able to connect to PyPI and the test suite should pass.

LibreSSL support

LibreSSL is a fork of OpenSSL. The fork was created off OpenSSL 1.0.1g by members of the OpenBSD team in 2014 in light of the heartbleed vulnerability. Since its inception several features deemed problematic or insecure were removed or replaced (SSL 2.0, SSL 3.0, improved CPRNG) or backported from OpenSSL and BoringSSL.

At the moment LibreSSL is not fully API compatible with OpenSSL 1.1.1. The latest release LibreSSL 3.3.2 is missing features and behaves differently in some cases. Mentionable missing or incompatible features include

• SHA-3, SHAKE, BLAKE2
• SSL_CERT_* environment variables
• security level APIs
• session handling APIs
• key logging API
• verified cert chain APIs
• OPENSSL_VERSION macro

This PEP proposed to remove any and all LibreSSL related workarounds from Python. In the future Python will not actively prohibit LibreSSL support with configure and compile time checks. But Python will not accept patches that add non-trivial workarounds or disable tests either.

BoringSSL

There are currently no plans to support BoringSSL.

Formalize supported OpenSSL versions

This PEP does not provide a set of formal rules and conditions under which an OpenSSL version is supported.

In general Python aims to be compatible with commonly used and officially supported OpenSSL versions. Patch releases of Python may not be compatible with new major releases of OpenSSL. Users should not expect that a new major or minor release of Python works with an OpenSSL version that is past its end-of-lifetime. Python core development may backport fixes for new releases or extend compatibility with EOLed releases as we see fit.

The new ABI stability and LTS policies of OpenSSL [9] should help, too.

Keep support for OpenSSL 1.1.0

It was suggested to keep support for OpenSSL 1.1.0 for compatibility with Debian 9 (Stretch). The proposal was rejected since it would complicated code cleanup and testing. Stretch is already out of regular security support and close to end of long-term support. By the time of Python 3.10 final release, Debian Buster and Debian Bullseye will be available.

Instead Python 3.10 will gain additional documentation and a new configure option --with-openssl-rpath=auto to simplify use of custom OpenSSL builds [11].