The attack is "differential analysis" -- essentially, if you have a black box encoder, carefully chosen plaintexts sent through the system can leak information,

The attack is "differential analysis" -- essentially, if you have a black box encoder, carefully chosen plaintexts sent through the system can leak information, and substantially weaken DES as described. Academic literature started discussing differential analysis in the early '90s if memory serves -- NSA helped harden against it in the 1970s! Current wisdom is that the NSA is not nearly so far ahead of the cryptography curve these days. But, it could just be speculation. :)