This is how i solved this problem
Download your APK to your PC in java jdk\bin folder
in my case C:\Program Files\Java\jdk1.7.0_121\bin
go to java jdk\bin folder and run cmd then
copy the following command in your cmd
keytool -list -printcert -jarfile yourapkname.apk
Copy the SHA1 value to your clip board
like this CD:A1:EA:A3:5C:5C:68:FB:FA:0A:6B:E5:5A:72:64:DD:26:8D:44:84
and open http://tomeko.net/online_tools/hex_to_base64.php to convert your SHA1 value to base64.
This is what Facebook requires
get the generated hash ” = ” and copy the key hash to the facebook app.