1. Key Laboratory of Cryptography of Zhejiang Province, School of Mathematics, Hangzhou Normal University, Hangzhou 311121, China
2. Department of Mathematics, BMS Institute of Technology and Management, Yelahanka, Bangalore 560064, India
3. Department of Mathematics, Global Campus, Jain (Deemed to Be University), Bangalore 562112, India
4. Department of Mathematics, Kuvempu University, Shivamogga 577451, India