Funding for this research was provided by:
National Natural Science Foundation of China (61672124, 61370145, 61173183)
the Password Theory Project of the 13th Five-Year Plan National Cryptography Development Fund (MMJJ20170203)
Article History
Received: 24 October 2018
Revised: 8 May 2019
Accepted: 15 May 2019
First Online: 5 June 2019