The license for software created by Whonix is the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version with additional terms applicable per GNU GPL version 3 section 7.
The additional terms are based on the Doom 3 license which is Debian refers to as `GPL-3+-with-id-software-additional-terms`, which is Debian DFSG [1] (The Debian Free Software Guidelines) approved and which is therefore suitable for Debian `main`. Whonix made applied minimal changes to it:
* Rewrite `The Doom 3 BFG Edition GPL Source Code` to the more common `this program` which is used throughout the GPL.
* Added a "trump clause" [2], in other words, any conflicts or disputes between the additional terms and the GPLv3 shall be resolved in favor of the GPLv3 by adding `Notwithstanding any other provision of this License` (as mentioned in GPL FAQ [3]) at the beginning of the additional terms.
[1] https://www.debian.org/social_contract#guidelines
[2] https://www.fsf.org/news/canonical-updated-licensing-terms
[3] https://www.gnu.org/licenses/gpl-faq.html#v3Notwithstanding
For more considerations, see also:
https://www.whonix.org/wiki/Dev/Licensing