Mandatory are file to be signed (To be signed)
and the two keys: publicKey and private key,
you can easy generate public key from private key
using "From PrivKey" button of PublicKey section,
there is no way in hell you can get private key from public key,
RSA 1024 is commonly used and sometimes (not often) even RSA 2048.
Rest of informations are optional and will be filled with some default values.
You can get all info from a stored keystore by clicking "Get info from file" button,
or only both keys (private and public key) from keystore by clicking "Both keys from file" button,
on both dialogs you will have "Load" keystore and "Save" keystore buttons.
On "Get info from file" you can also select a jar/apk/zip archive
cotainig the file "\META-INF\CERT.RSA" but obiously this file contains
almost all info except private key.
"Calc size" button from PrivateKey section will calculte RSA Size
from PublicKey or PrivateKey, the size of RSA is equal with
the size of modulus.
If you click "PublicKey:" label or on "PrivateKey:" label wil show infos
about these keys: Modulus and PublicExponent respective Modulus and PrivateExponent.

Sign a file in four steps:
1. Select file "To be signed" using "..." button (browse button).
or drag and drop the file on textbox.
2. Click on "Generate Keys" button to generate public and private key.
3. Click on "Sign" button.
4. A new signed file will be created on old_file_name+"_signed"+oldextension.

Only for V.I.P