Why do I have to reenter my passwords after moving HDD between Macs?
The problem lies in changes to the OS X Keychain apparently introduced with the extended iCloud support in Mavericks. 

The Keychain has a new chain called Local items. The local items are stored in an sqlite database in a folder corresponding to the hardware UUID of the mainboard. Additionally it appears to be encrypted is a way that involves details from the mainboard (probably the UUID). 

There are various people reporting to be unable to recover their local items after a hardware failure or after moving to new hardware. The only workaround to be affected by this problem appears to be enabling iCloud synchronization for the Keychain, thus the saved passwords are synced from the cloud to any new hardware. Of course, that is not helpful for people who are not interested in using iCloud.

See also:


https://discussions.apple.com/thread/6543257
New &quot;Local Items&quot; Keychain in Mavericks: What&#39;s it all about?
http://www.faqssys.info/how-do-i-migrate-my-keychains-local-items-to-a-new-mac/
http://forums.macrumors.com/threads/data-migration-local-keychain-passwords-not-appearing.1905840/


If anybody knows a way to actually recover/decrypt the local items after moving one's account to a different hardware, I'd be happy to learn about it.