People are discounting, I think, the lulz factor in pretending to be working for NK. Just sayin'.

What would a "hard link" be? A signed confession from the head of the DPRK military? Under the circumstances, barring classified intelligence (like the NSA may have), we are as sure as we can be.

So we are unsure.

Out of curiosity, what evidence would convince you?

I don't know - isn't this an issue with the erosion of trust towards the administration and "domain experts", something they can only blame themselves for?

More importantly, why do you want people to be convinced of this? What difference does it make? If it is used as some sort of justification for (more?) economic sanctions or an attack, then I don't think any realistic hacking attempt is going to be enough. If you just want this attributed to NK, what is the point? If people don't know enough about the situation to be sure, and they have no trust in any authority on the subject, then the way forward would be for an authority to build up trust with those people and then claim it is attributed to NK.

Absolute certainty that this would not be used as an excuse to launch military attacks would be a start.

Collin Powell got quite a lot of tonnage I mean mileage out of a cartoon drawing. Just draw him a picture.

Who is "we" here? There are many levels of bullshit between knowledgeable folk at NSA and me. Far too many for me to be sure of anything.