What is OpenSSL VPN?

OpenSSL is an open-source implementation of the SSL and TLS protocols. The core library, written C programming language, implements the basic cryptographic functions and provides various utility functions. Wrappers allowing the use of the OpenSSL library in a variety of computer languages are available.
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Versions are available for most Unix-like operating systems (including Solaris, Linux, Mac OS X and the various open source BSD operating systems), OpenVMS and Microsoft Windows. IBM provides a port for the System i (OS/400). OpenSSL is based on SSLeay by Eric A. Young and Tim Hudson, development of which unofficially ended around December 1998, when Young and Hudson both started to work for RSA Security.

FIPS 140-2 compliance

As of December 2012, OpenSSL is one of two open source programs to be involved with validation under the FIPS 140-2 computer security standard by the National Institute of Standards and Technology's (NIST) Cryptographic Module Validation Program (CMVP). (OpenSSL itself is not validated, but a component called the OpenSSL FIPS Object Module, based on OpenSSL, was created to provide many of the same capabilities).
A certificate was first awarded in January 2006 but revoked in July 2006 "when questions were raised about the validated module’s interaction with outside software." The certification was reinstated in February 2007.

Licensing

OpenSSL is "dual licensed" under the OpenSSL License and the SSLeay License. The OpenSSL License is Apache License 1.0 and SSLeay License is a 4-clause BSD License. The common usage of the term dual-license is that the user may pick which license they wish to use. However, OpenSSL documentation uses the term dual-license to mean that both licenses apply.

As the OpenSSL License is Apache License 1.0, but not Apache License 2.0, it requires the phrase This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. (http://www.openssl.org/) to appear in advertising material and any redistributions (Sections 3 and 6 of the OpenSSL License). Due to this restriction, the OpenSSL License and the Apache License are incompatible with the GPL. Some GPL developers have added an OpenSSL exception to their licenses specifically allowing OpenSSL to be used with their system. GNU Wget and climm both use such exceptions. Some packages (like Deluge) explicitely modify the GPL license by adding an extra section at the beginning of the license documenting the exception. Other packages use the LGPL licensed GnuTLS which performs the same task.

Vulnerability in the Debian implementation

In order to keep a warning from being issued by the Valgrind analysis tool, a maintainer of the Debian distribution applied a patch to the Debian implementation of the OpenSSL suite, which inadvertently broke its random number generator in the process. The broken version was included in the Debian release of September 17, 2006 (version 0.9.8c-1). Any key generated with the broken random number generator, as well as data encrypted with such a key, was compromised. The error was reported by Debian on May 13, 2008.
On the Debian 4.0 distribution (etch), these problems were fixed in version 0.9.8c-4etch3 and for the Debian 5.0 distribution (lenny), these problems were fixed in version 0.9.8g-9.