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OpenSSL is a robust, commercial-grade, full-featured Open Source Toolkitfor the TLS (formerly SSL), DTLS and QUIC (currently client side only)protocols.

The protocol implementations are based on a full-strength general purposecryptographic library, which can also be used stand-alone. Also included is acryptographic module validated to conform with FIPS standards.

OpenSSL is descended from the SSLeay library developed by Eric A. Youngand Tim J. Hudson.

The official Home Page of the OpenSSL Project iswww.openssl.org.

• Overview
• Download
• Build and Install
• Documentation
• License
• Support
• Contributing
• Legalities

The OpenSSL toolkit includes:

• libsslan implementation of all TLS protocol versions up to TLSv1.3 (RFC 8446),DTLS protocol versions up to DTLSv1.2 (RFC 6347) andthe QUIC (currently client side only) version 1 protocol (RFC 9000).

• libcryptoa full-strength general purpose cryptographic library. It constitutes thebasis of the TLS implementation, but can also be used independently.

• opensslthe 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 fromopenssl-library.org/source/.The OpenSSL project does not distribute the toolkit in binary form.

However, for a large variety of operating systems precompiled versionsof the OpenSSL toolkit are available. In particular, on Linux and otherUnix operating systems, it is normally recommended to link against theprecompiled shared libraries provided by the distributor or vendor.

We also maintain a list of third parties that produce OpenSSL binaries forvarious Operating Systems (including Windows) on theBinaries page on ourwiki.

Although testing and development could in theory also be done usingthe source tarballs, having a local copy of the git repository withthe entire project history gives you much more insight into thecode base.

The main OpenSSL Git repository is private.There is a public GitHub mirror of it atgithub.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 fromthe GitHub mirror using

git clone https://github.com/openssl/openssl.git

If you intend to contribute to OpenSSL, either to fix bugs or contributenew features, you need to fork the GitHub mirror and clone your public forkinstead.

git clone https://github.com/yourname/openssl.git

This is necessary because all development of OpenSSL nowadays is done viaGitHub pull requests. For more details, seeContributing.

After obtaining the Source, have a look at theINSTALL file fordetailed instructions about building and installing OpenSSL. For someplatforms, the installation instructions are amended by a platform specificdocument.

• 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 foundin theossl-guide-migration(7ossl) manual page.

There are some README.md files in the top level of the source distributioncontaining 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
• Information about the legacy OpenSSL Engine architecture

There are some tutorial and introductory pages on some important OpenSSL topicswithin theOpenSSL Guide.

The manual pages for the master branch and all current stable releases areavailable online.

• OpenSSL master
• OpenSSL 3.0
• OpenSSL 3.1
• OpenSSL 3.2

There are numerous source code demos for using various OpenSSL capabilities in thedemos subfolder.

There is a Wiki atwiki.openssl.org which is currently not very active.It contains a lot of useful information, not all of which is up-to-date.

OpenSSL is licensed under the Apache License 2.0, which means thatyou are free to get and use it for commercial and non-commercialpurposes as long as you fulfill its conditions.

See theLICENSE.txt file for more details.

There are various ways to get in touch. The correct channel depends onyour requirement. See theSUPPORT file for more details.

If you are interested and willing to contribute to the OpenSSL project,please take a look at theCONTRIBUTING file.

A number of nations restrict the use or export of cryptography. If you arepotentially subject to such restrictions, you should seek legal advice beforeattempting to develop or distribute cryptographic code.

Copyright (c) 1998-2025 The OpenSSL Project Authors

Copyright (c) 1995-1998 Eric A. Young, Tim J. Hudson

All rights reserved.