Keycheck orig.bin hacked.bin
That is the proper syntax.
If you open it in a hex editor, goto $4000, then you will see 01 11 11 11 11 then a 16-byte key location (all FF's if no key) 02 EE EE EE EE then a 16-byte key location 03 11 11 11 11 then a 16-byte key location. This will continue until your key is in one of the 16-byte key locations. After your key is stated, you should have all FF's to $5FFF. Your key can be anywhere between $4000-5FFF but will typically be between $4000-4400.
Caster.