Seed processing safety rules

- read carefully and obey before any action -

In general you should never store or process your seed on a computer or any mobile device.
Just never ever!
End of story.
Unfortunately calculating SHA-256 is practically impossible without using a computer. So if you decide to do it, you should be extremely careful and strictly follow the safety rules!
You should always assume the worst case scenario while handling with your seed. It means you should always assume that someone is trying to trick you and steal your seed. You should keep this fact in mind at every single step! No matter if you deal with your best friend, website or even software made by Microsoft.
To exclude the possibility of stealing your seed, you shoud always operate on an offline computer without the Internet (and any other network) connection. If you did not write the application code, you never know how does it work. You never know if the application will not send your seed to someone else. For the same reason you should never put your seed to any website calculator. This would be insane!
But staying offline is not enough!
You never know if the application will not try to store your seed and send it to someone as soon as your system restores the Internet connection in the future. In the worst case scenario you should always assume this. Furthermore, even if the application is 100% secure (you wrote your own code), you still never know if your operating system is free of spying malware. And if so, then the consequence is exactly the same.
To avoid such a risk and stay secure, you should always follow these steps:
  1. Copy the application to the computer
  2. Disconnect the Internet (and any other possible network!)
  3. Put your 23 seed words and calculate the checksum
  4. Erase all the data from HDD, erase the calculating application including system Recycle Bin (Trash Bin)
  5. Restore operating system to the factory settings (eliminates the risk of any spying malware existence in your system including the calculating application)
  6. Connect the Internet
Restoring system to the factory settings is much inconvenient and implies a lot of future work because you need to install all your software again. But only such a manner guarantees you safety.
If you want to avoid restoring system to the factory setting and you are absolutely sure that your system is free of malware, then you can follow this steps:
  1. Create the system restore point
  2. Copy the application to the computer
  3. Disconnect the Internet
  4. Put your 23 seed words and calculate the checksum
  5. Erase all the data from HDD, erase the application including system Recycle Bin (Trash Bin)
  6. Restore system to the previously created point (it DOES NOT eliminate the risk of any spying malware existence in your system, but eliminates the risk that calculating application is trying to steal your seed)
  7. Connect the Internet
If you have any old computer that you no longer use, it would be very convenient to use it as the only tool to handle with your seed. Then you will not need to connect it to the Internet anymore. And even restoring such a system to the factory settings should not be any inconvenience.

If you follow one of the ground rules above to handle with your seed, you will stay safe from any Internet risks. The only potential risk will remain the manner of choosing your own 23 words and potential way of storing it (as long as you don't store it in your mind).

Remember that all the UNIX/LINUX based operating systems are by design much more secure than any Windows.