Original: The S-Box design criteria were eventually published (Don Coppersmith, 1994) after the public rediscovery of differential cryptanalysis, showing that they had been carefully tuned to increase resistance against this specific attack.
Simplified: In 1994, the S-Box design criteria were finally published by its designers after the public rediscovery of differential cryptanalysis, showing that they had been carefully tuned the design to increase resistance against differential cryptanalysis attacks.