Reinstall processes

[Chris Zakelj]

Silly question I can't seem to find the answer for:
When reinstalling a system rather than doing upgrades, how does one
properly migrate encrypted info?  Does the keygen process on a first
boot create a key that renders the previous hashes (passwords being the
most obvious) useless, or are those independent of the keys being
generated?  If I need to bring the old keys over, where do they live?