Recently i came across this issue while setting up facebook integration on Android. All the guides are essential reading but do not tell you how to get your release hash key to put into the app settings on facebook.
Providing you have followed the instructions on https://developers.facebook.com/docs/guides/mobile/android_hackbook/#start you should be in a position to logon with facebook while debugging the device. However when it comes to deploying your app and signing with a keystore you must do the following
keytool -exportcert -alias [KEYSTORE ALIAS] -keystore [PATH TO KEYSTORE] | openssl sha1 -binary | openssl base64
This will give a hash key just like the debug key. Now just paste the key into the settings of your app on facebook and everything should work correctly.