Simplest way to generate hash key.
Requirement: SHA1 Key
You can get SHA1 Key from your keystore file by two ways
1) Locate your keystore file, open command prompt on that location then use below mentioned command
keytool -list -v -keystore {keystore_name} -alias {alias_name}
and then enter your password then it will return md5, sha1 and sha256 key.
OR
2) By running signingReport
Refer below image.
after you run the file your output will be generated containing required sha1 key.
After you get the required SHA1 Key
Then goto
http://tomeko.net/online_tools/hex_to_base64.php
and paste your sha1 key
and finally you will get Required HashKey which you can use it to apply on facebook.