I am currently using a highly complex method to store a set of 24 mnemonic words. Decoding the mnemonic requires 20 minutes.
I am considering why not use a simpler approach?
For example, writing down 15 words on papers, and storing the remaining 9 words on an encrypted USB drives and online emails. Certainly, both the paper documents and electronic file should be kept with multiple copies.
Question: Given the first 15 words out of 24, can a hacker crack the wallet?
I ask chatGPT, and it say that is secure. However, considering that AI models often give unreliable information, it would be better to seek advice from friends on this website. Thanks!
Adding passphrase is better, and some message is obtained here
https://blog.trezor.io/is-your-passphrase-strong-enough-d687f44c63af The official Trezor website has calculated the security length of a passphrase. It states that a passphrase containing characters from 0-9, a-z, A-Z is considered secure with a length of 10 characters. With 62^10 possible combinations, this is equivalent to approximately 5.41 words, or 2048^5.41.
Keep in mind that increased security comes with increased responsibilities. There have been complains about losing seed phrase but there hasn't been a case when wallet was cracked by someone via bruteforcing (unless seed owner made a huge mistake). For sure, you have to save it securely but don't save it in a way that you'll lose access on it.
Also, if you are so afraid of your wallet getting cracked, then keep in mind that even if it's possible to crack your wallet in a year, you still have a timeframe that allows you to create a new wallet and transfer coins from old wallet to new one. Even if you know that you lost some part of your seeds and attacker will crack it in a day, you still have time to create a new one and transfer from old to new wallet.
Also, keep in mind that if you use 24 words seed phrase, even if you reveal words in unordered way, hacker still won't be able to crack your wallet, but will be able to crack if you use 12 words seed phrase and reveal all of them.
Storing partial unencrypted wallet data on a fingerprint-encrypted USB drive or writing it directly on paper doesn't make much difference. These fingerprint-encrypted USB drives are specifically designed for protecting corporate trade secrets, and I don't think they can be easily cracked.
Digital storage has other shortcomings that just being hacked/cracked. For example hardware problems that is where the USB disk is harmed either physically or due to electrical issues or other things and the data on it becomes inaccessible. Or we have the data decay/degradation by passage of time.
He can probably buy some waterproof, fireproof, extreme conditions proof safe and store his USB there. Btw instead of storing something on USB disk, if I were him, I would buy Coldcard or Passport wallet.