Hello,
Your serial number is unique to your MacBook Pro and doesn't need to be posted on Apple Support Communities. In regards to the hash code, are you being stopped by a firmware password on your Mac? If you see a padlock and a password field when trying to boot Recovery Mode, the previous owner set a firmware password on your Mac, and it is impossible to boot any external media or Recovery Mode without that password. Unfortunately, only Apple is able to remove a forgotten firmware password, and if you are being stopped by an unknown firmware password, you'll need to take your Mac to the nearest Apple Store or Apple Authorized Service Provider.