Complex sentence: It was not until 2011 that the first open-source implementation appeared, and in 2013, Security Innovation exempted open source projects from having to get a patent license, and released an NTRU reference implementation under the GPL v2.
Split into simpler sentences: It was not until 2011 that the first open-source implementation appeared. In 2013, Security Innovation exempted open source projects from having to get a patent license, and released an NTRU reference implementation under the GPL v2.