Evidence of the NSAKEY being a backdoor includes some description of how the backdoor might work...
It would only work one way with an API relying on a PKI with a single CA, zero transparency, and trusted keys named after spy agencies suddenly appearing out of nowhere. I'm gonna bail here, because I'm now not sure if you honestly don't know what the CAPI was in relation to the NSAKEY - or if you're trying to waste my time by getting me to explain the most basic principles of public key infrastructure.