Crate openssl

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Bindings to OpenSSL

This crate provides a safe interface to the popular OpenSSL cryptography library. OpenSSL versions 1.0.1 through 3.x.x and LibreSSL versions 2.5 through 3.7.x are supported.


Both OpenSSL libraries and headers are required to build this crate. There are multiple options available to locate OpenSSL.


If the vendored Cargo feature is enabled, the openssl-src crate will be used to compile and statically link to a copy of OpenSSL. The build process requires a C compiler, perl (and perl-core), and make. The OpenSSL version will generally track the newest OpenSSL release, and changes to the version are not considered breaking changes.

openssl = { version = "0.10", features = ["vendored"] }

The vendored copy will not be configured to automatically find the system’s root certificates, but the openssl-probe crate can be used to do that instead.


The openssl-sys crate will automatically detect OpenSSL installations via Homebrew on macOS and vcpkg on Windows. Additionally, it will use pkg-config on Unix-like systems to find the system installation.

# macOS (Homebrew)
$ brew install openssl@3

# macOS (MacPorts)
$ sudo port install openssl

# macOS (pkgsrc)
$ sudo pkgin install openssl

# Arch Linux
$ sudo pacman -S pkg-config openssl

# Debian and Ubuntu
$ sudo apt-get install pkg-config libssl-dev

# Fedora
$ sudo dnf install pkg-config perl-FindBin openssl-devel

# Alpine Linux
$ apk add pkgconfig openssl-dev

# openSUSE
$ sudo zypper in libopenssl-devel


A set of environment variables can be used to point openssl-sys towards an OpenSSL installation. They will override the automatic detection logic.

  • OPENSSL_DIR - If specified, the directory of an OpenSSL installation. The directory should contain lib and include subdirectories containing the libraries and headers respectively.
  • OPENSSL_LIB_DIR and OPENSSL_INCLUDE_DIR - If specified, the directories containing the OpenSSL libraries and headers respectively. This can be used if the OpenSSL installation is split in a nonstandard directory layout.
  • OPENSSL_STATIC - If set, the crate will statically link to OpenSSL rather than dynamically link.
  • OPENSSL_LIBS - If set, a :-separated list of library names to link to (e.g. ssl:crypto). This can be used if nonstandard library names were used for whatever reason.
  • OPENSSL_NO_VENDOR - If set, always find OpenSSL in the system, even if the vendored feature is enabled.

Additionally, these variables can be prefixed with the upper-cased target architecture (e.g. X86_64_UNKNOWN_LINUX_GNU_OPENSSL_DIR), which can be useful when cross compiling.

§Feature Detection

APIs have been added to and removed from the various supported OpenSSL versions, and this library exposes the functionality available in the version being linked against. This means that methods, constants, and even modules will be present when building against one version of OpenSSL but not when building against another! APIs will document any version-specific availability restrictions.

A build script can be used to detect the OpenSSL or LibreSSL version at compile time if needed. The openssl-sys crate propagates the version via the DEP_OPENSSL_VERSION_NUMBER and DEP_OPENSSL_LIBRESSL_VERSION_NUMBER environment variables to build scripts. The version format is a hex-encoding of the OpenSSL release version: 0xMNNFFPPS. For example, version 1.0.2g’s encoding is 0x1_00_02_07_0.

For example, let’s say we want to adjust the TLSv1.3 cipher suites used by a client, but also want to compile against OpenSSL versions that don’t support TLSv1.3:


openssl-sys = "0.9"
openssl = "0.10"

use std::env;

fn main() {
    if let Ok(v) = env::var("DEP_OPENSSL_VERSION_NUMBER") {
        let version = u64::from_str_radix(&v, 16).unwrap();

        if version >= 0x1_01_01_00_0 {

use openssl::ssl::{SslConnector, SslMethod};

let mut ctx = SslConnector::builder(SslMethod::tls()).unwrap();

// set_ciphersuites was added in OpenSSL 1.1.1, so we can only call it when linking against that version


  • Low level AES IGE and key wrapping functionality
  • Defines the format of certificates
  • Base64 encoding support.
  • BigNum implementation
  • Symmetric ciphers.
  • The symmetric encryption context.
  • SMIME implementation using CMS
  • Interface for processing OpenSSL configuration files.
  • Shared secret derivation.
  • Diffie-Hellman key agreement.
  • Digital Signatures
  • Elliptic Curve
  • Low level Elliptic Curve Digital Signature Algorithm (ECDSA) functions.
  • Message encryption.
  • Envelope encryption.
  • Errors returned by OpenSSL library.
  • Message digest (hash) computation support.
  • Message digest algorithms.
  • The message digest context.
  • Utilities to safely compare cryptographic values.
  • A collection of numerical identifiers for OpenSSL objects.
  • PKCS #12 archives.
  • Public/private key processing.
  • The asymmetric encryption context.
  • Utilities for secure random number generation.
  • Rivest–Shamir–Adleman cryptosystem
  • The SHA family of hashes.
  • Message signatures.
  • SSL/TLS support.
  • High level interface to certain symmetric ciphers.
  • Build and version information.
  • The standard defining the format of public key certificates.