OpenSSL is a robust, commercial-grade, full-featured Open Source Toolkit for the Transport Layer Security (TLS, formerly SSL), Datagram TLS (DTLS), and QUIC protocols.
The protocol implementations are based on a full-strength general purpose cryptographic library, which can also be used stand-alone. Also included is a cryptographic module validated to conform with FIPS standards.
OpenSSL is descended from the SSLeay library developed by Eric A. Young and Tim J. Hudson.
The official Home Page of the OpenSSL Project is www.openssl.org.
The OpenSSL toolkit includes:
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libssl an implementation of all TLS protocol versions up to TLSv1.3 (RFC 8446), DTLS protocol versions up to DTLSv1.3 (RFC 9147) and the QUIC version 1 protocol (RFC 9000).
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libcrypto a full-strength general purpose cryptographic library. It constitutes the basis of the TLS implementation, but can also be used independently.
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openssl the OpenSSL command line tool, a Swiss Army knife for cryptographic tasks, testing and analyzing. It can be used for
- creation of key parameters
- creation of X.509 certificates, CSRs and CRLs
- calculation of message digests
- encryption and decryption
- SSL/TLS/DTLS and client and server tests
- QUIC client tests
- handling of S/MIME signed or encrypted mail
- and more...
Source code tarballs of the official releases can be downloaded from openssl-library.org/source/. The OpenSSL project does not distribute the toolkit in binary form.
However, for a large variety of operating systems precompiled versions of the OpenSSL toolkit are available. In particular, on Linux and other Unix operating systems, it is normally recommended to link against the precompiled shared libraries provided by the distributor or vendor.
We also maintain a list of third parties that produce OpenSSL binaries for various Operating Systems (including Windows) on the Binaries page on our wiki.
Although testing and development could in theory also be done using the source tarballs, having a local copy of the git repository with the entire project history gives you much more insight into the code base.
The main OpenSSL Git repository is private. There is a public GitHub mirror of it at github.com/openssl/openssl, which is updated automatically from the former on every commit.
A local copy of the Git repository can be obtained by cloning it from the GitHub mirror using
git clone https://github.com/openssl/openssl.git
If you intend to contribute to OpenSSL, either to fix bugs or contribute new features, you need to fork the GitHub mirror and clone your public fork instead.
git clone https://github.com/yourname/openssl.git
This is necessary because all development of OpenSSL nowadays is done via GitHub pull requests. For more details, see Contributing.
After obtaining the Source, have a look at the INSTALL file for detailed instructions about building and installing OpenSSL. For some platforms, the installation instructions are amended by a platform specific document.
- Notes for UNIX-like platforms
- Notes for Android platforms
- Notes for Windows platforms
- Notes for the DOS platform with DJGPP
- Notes for the OpenVMS platform
- Notes on Perl
- Notes on Valgrind
Specific notes on upgrading to OpenSSL 3.x from previous versions can be found in the ossl-guide-migration(7ossl) manual page.
There are some README.md files in the top level of the source distribution containing additional information on specific topics.
- Information about the OpenSSL QUIC protocol implementation
- Information about the OpenSSL Provider architecture
- Information about using the OpenSSL FIPS validated module
There are some tutorial and introductory pages on some important OpenSSL topics within the OpenSSL Guide.
The manual pages for the master branch and all current stable releases are available online.
There are numerous source code demos for using various OpenSSL capabilities in the demos subfolder.
There is a GitHub Wiki which is currently not very active.
OpenSSL is licensed under the Apache License 2.0, which means that you are free to get and use it for commercial and non-commercial purposes as long as you fulfill its conditions.
See the LICENSE.txt file for more details.
There are various ways to get in touch. The correct channel depends on your requirement. See the SUPPORT file for more details.
If you are interested and willing to contribute to the OpenSSL project, please take a look at the CONTRIBUTING file.
A number of nations restrict the use or export of cryptography. If you are potentially subject to such restrictions, you should seek legal advice before attempting to develop or distribute cryptographic code.
Copyright (c) 1998-2026 The OpenSSL Project Authors
Copyright (c) 1995-1998 Eric A. Young, Tim J. Hudson
All rights reserved.