mister chang, when and why did you start following north korea? very : well, i was interested in chinese foreign-policy. and their most interesting bilateral relationship is with north korea. on many levels, it doesn't make sense. so i was just fascinated by what was going on. i was looking at the between beijing and pyongyang. host: should the u.s. retaliate? guest: well, north korea is responsible from the sack from all that we can tell. for instance, the code that was used against sony pictures entertainment was virtually identical to the car that was used against south korean businesses in march and june of last year. they trace those attacks back to north korea. first refused ans their involvement, then they had a very unconvincing -- it wasn't me. clearly, it was the north koreans. and we're going to find out from the administration today. they probably will directly attributed to them. host: what kind of response be from the u.s., in your view? be a military response, a cyber response? guest: i don't think it to be a military response or a