How did the complexity focus shift when moving from warded locks to pin-tumbler locks concerning the key?

Answer

From making the lock interior complex to making the key exterior complex

The innovation moved from making the lock interior (the wards) more complex to making the key exterior more complex, as the key's cuts now had to align specific moving parts perfectly.

How did the complexity focus shift when moving from warded locks to pin-tumbler locks concerning the key?
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