Yes, the NSA created sboxes that were resistant to differential cryptanalysis. I was asking for a citation in regard to the claim that: >The small key size was

Yes, the NSA created sboxes that were resistant to differential cryptanalysis. I was asking for a citation in regard to the claim that: >The small key size was later discovered to be right around the actual security level the cipher provides (larger key sizes would not have improved security by much). I have never heard this claim before and without any source backing it up I am liable to doubt it.