Decoded
解密 (original)
A math genius gets recruited by Chinese spy agency to crack a complex coded message in the early republican era.
Starring Ying Er, Chen Xuedong, Jing Chao, Zhang Zhehan, Yin Xiaotian, Guo Jingfei, Yang Yi Tong, Wang Yanyang, Ady An, Apollo Yu
Watch "Decoded" from streaming services Rakuten Viki, Tubi TV released in 2016. It's a drama and mystery show, and has a rating of 7.7 out of 10 from Imdb which is usually fine for this kind of show, and is currently available to watch for free.