I am setting up my hardware wallet, and have written down my mnemonic seed phrase physically, but also want a way of accessing it from my computer.
If I add all the seed words together, and hash it by a specific combination of the existing words, would it be safe to store on a computer?
The outputs of hash functions cannot be reversed. So what is the point of storing the hash of your seed? Perhaps you mean an encrypted version of your seed? That would be storing the ciphertext of your seed. You could do that but just so you know there's already an encrypted version of your seed stored in your wallet file. Otherwise there would be no way for the wallet to sign spending transactions.
Depending on your computer security, if your computer hacked even if you hashed it or whatever did you do, they will access it.
even if you did store it physically, if your computer infected with any keylogger they will see every letter you type.
if you don't have any idea how to secure your computer, just keep it offline and create your transactions then broadcast it somewhere.
If all of the information needed to recreate your mnemonic seed phrase is stored digitally in an online computer, then you will be greatly increasing the attack surface for any potential hacker. There are ways you could store this digital data more securely, but ultimately having it stored in an online computer will ALWAYS be less secure than having a true 'cold wallet', whose keys/seed phrase have never existed on an online machine.
If you are just storing the hash of your seed phrase, then that would not be enough for an attacker to steal your coins. However, you will need to input your seed phrase into some device in order to run the hash function, so something simple like a keylogger could skim your seed phrase when you do so. You could run the hash function on a permanently offline machine, and then transfer the output value to an online machine for storage, but I'm not sure what the point of doing so would be. A hash of the seed phrase will not help you restore your wallet later, you'll need the seed phrase itself to do so.
