A. Petzoldt, M.-S. Chen, B.-Y. Yang, C. Tao, and J. Ding, "Design Principles for HFEv- Based Multivariate Signature Schemes," Advances in Cryptology - ASIACRASIACYPT 2015 - 21st International Conference on the Theory and Application of Cryptology and Information Security, Auckland, New Zealand, November 29 - December 3, 2015, Proceedings, Part I., Lecture Notes in Computer Science, volume 9452, Tetsu Iwata and Jung Hee Cheon, editors, Springer, pages 311-334, November 2015
http://www.iis.sinica.edu.tw/papers/byyang/19342-F.pdf