Step-by-step Solution:

Divide the word into six sets of two letters each and label these sets from 1 to 6. Then, the code contains these sets in the order 4, 3, 5, 2, 6, 1 with the letters of sets 3, 2, 1 written in a reverse order. Thus, we have : VI SH WA NA TH AN => NA AW TH HS AN IV