3 of 3 replaced http://superuser.com/ with https://superuser.com/

Verbatim:

In Mac OS X, keychain files are stored in ~/Library/Keychains/, /Library/Keychains/, and /Network/Library/Keychains/,

source: http://en.wikipedia.org/wiki/Keychain_(Apple)

edit Sorry, I didn't understand that you were asking for the login password...

For that, there is this similar question elsewhere, with a good answer...