Strong evidence is lacking to make any conclusion, including that NK is responsible.
There are incentives to falsely place blame on NK and there is a wealth of history demonstrating that type of behavior. In particular the US may have wanted to attack NK for some time but lacked a way to galvanize the public's support. Opportunities to get backing for war are rare, and so there is good reason to think that the government would try to capitalize on them. The fact that the government isn't releasing evidence suggests that it is weak or non-existent.
There is also good reason to believe that NK did do the hack.
There are incentives to falsely place blame on NK and there is a wealth of history demonstrating that type of behavior. In particular the US may have wanted to attack NK for some time but lacked a way to galvanize the public's support. Opportunities to get backing for war are rare, and so there is good reason to think that the government would try to capitalize on them. The fact that the government isn't releasing evidence suggests that it is weak or non-existent.
There is also good reason to believe that NK did do the hack.