OpenSSL has completed a re-licensing effort, resulting in adoption of Apache 2.0. The project announced this effort in 2015. The project got permission from contributors via a CLA.
The OpenSSL/SSLeay license was a non-standard permissive license, which included attribution clauses of the kind deprecated in Apache 1.0, such as:
All advertising materials mentioning features or use of this software must display the following acknowledgment: "This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
and the mysterious statement:
The licence and distribution terms for any publically available version or derivative of this code cannot be changed. i.e. this code cannot simply be copied and put under another distribution licence * [including the GNU Public Licence.]
This caused many to wonder whether the license was truly permissive. Over the years, users (and reluctantly, their lawyers) accepted it as permissive, but not without some angst.
Kudos to the project for clarifying and harmonizing the license for this ubiquitous bit of software.
