[mrguyorama]

>They are also likely protected against a number of attacks that aren't public

For reference, see DES, where the NSA adjusted the algorithm to protect from a not publicly understood differential cryptanalysis attack. Many people claimed that the adjustment by the NSA was clear backdooring, though we know that was not true.

It was however purposely deficient in the length of its key, allegedly because "it was good enough" and for export reasons, but also because the NSA considered it easy enough to brute force.