Another reputable source here.

http://www.economist.com/news/business-and-finance/21698060-craig-wright-reveals-himself-as-satoshi-nakamoto

It says he published proof in a blog post. Doesn't seem to have a link.

Well, I know what *I'm* doing on the internet for the next hour!

(Or rather, until someone savvier beats me to it)

ETA apparently the above is a 'taster', the meatier article is:

http://www.economist.com/news/briefings/21698061-craig-steven-wright-claims-be-satoshi-nakamoto-bitcoin

Off to find that blog...