The 1998 Constitution of The Republic of Sudan, does not explicitly mention freedom of association, however, Article 26 protects the freedom of succession and organization which is understood to be freedom of Association. The Following draft in the 2005 Constitution does specify freedom of association in article 40.

CIA World Factbook. Sudan. https://www.cia.gov/the-world-factbook/countries/sudan/#government

Prior Constitution of The Republic of Sudan. 1998. University of Minnesota, Human Rights Library. http://hrlibrary.umn.edu/research/sudpriorconst.html

Constitute Project. Constitution of the Republic of Sudan. 2005. https://www.constituteproject.org/constitution/Sudan_2005