I don't have references, apologies, but in the 90s and 00s there were reports of NSA making polite suggestions to private companies to improve their cryptosyste

I don't have references, apologies, but in the 90s and 00s there were reports of NSA making polite suggestions to private companies to improve their cryptosystems and secure crucial infrastructure. That advice was always viewed with suspicion and verified, but was often genuinely helpful. Over time NSA started using that influence more and more to implant back doors. Dual_EC_DRBG is a particularly well documented example. I assume now most companies absolutely don't trust the NSA as a partner in designing security systems since they have worked so often to undermine them.