Nick Szabo  🔑

You still have to backup the PKs

For backup paper wallet or, if you have a lot, steel-letter wallet.

but if we store on paper, when we want to make a transaction we need to type the pk on a device that could be conpromised and it could expose us to hack. Is cold wallet hardware a good solution or not ?

Paper wallet is the backup seed for the hardware wallet. Hardware wallet is what you make transactions with.

i know that but @NickSzabo4 just recommand to write private key on paper, he do not recommande hardware wallet, unless he make a new post

What about mutli-sig wallet systems with the user in control of 1 key and the app control of the other

Depends on the setup. Ideally not a 2-of-2 (or similar) where a lost key by the webw. provider results in lost funds. If you take away that risk, you won't add much security. Also, privacy is very likely completely exposed to the webwallet. Local key management matters also.

I thought about a custom P2SH wallet with a 2/2 and a master key that belongs to the user. if webw is compromised then the user can spend the UTXO using the master key.

Where is the additional security? You need to generate and protect two seeds. Where is the additional security over a 2-of-2 with two hardware wallets?

A compromised webw wouldn’t result in loss of funds and the user gets the convenience of a webw.

But this would mean, If the website's db has gone down or corrupted, You will lose your funds forever .

If you give the user an additional master key that they can store like a paper wallet. They will be able to spend those UTXO in case of a compromised wallet app