There is a lot of circumstancial evidence that supports the backdoor story, e.g. the extended random extension or the events around RSA Inc. and Juniper. I mean

There is a lot of circumstancial evidence that supports the backdoor story, e.g. the extended random extension or the events around RSA Inc. and Juniper. I mean... it's a question what would qualify as prooof (a copy of "here are our secret numbers" from inside NSA maybe), but basically: There are a lot of events that definitely happened that make a lot of sense with the backdoor story and make no sense otherwise.