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(as others have noted multi-sig schemes may be a better option but here are a few infos regarding your questions) > 1: Create a seed phrase with dices You can

(as others have noted multi-sig schemes may be a better option but here are a few infos regarding your questions) > 1: Create a seed phrase with dices You can do that but you'll need a way to generate the checksum for the seed phrase. A 24 words BIP39 seed contains 264 bits (24 x 11 bits): 256 bits for the seed and 8 bits for the checksum. > There is not an easy way to check if the hardware wallet really has no internet connectivity. Indeed but you can at least open / disassemble some of them easily (there are even docs by the manufacturers explaining how to verify that the hardware wallet's PCB looks legit). Seed exfiltration, even without connectivity, is an issue too. And some hardware wallets are extremely noisy and impossible to use totally offline (there are mandatory firmware upgrades and mandatory connectivity needed to install the "apps" that allow to sign transactions), so you have to trust the vendor. > There is no way to check if the hardware wallet really uses the seed phrase to create the extended public key. Yes there is. Use an airgapped/offline computer which has physically no network connectivity options (no wifi / no ethernet / no bluetooth / no nothing), no HDD, booted from, say, a live Linux CD with contains for example Ian Coleman's BIP39 tools. Then you enter your seed and verify that the extended public key / keys derived is the same as the one shown by your hardware wallet. Data exfiltration from such a computer is still technically possible but I wouldn't worry too much about it: you power that computer for a few minutes, turn it off, and you'll be fine.

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olalonde 4y ago
> You can do that but you'll need a way to generate the checksum for the seed phrase. A 24 words BIP39 seed contains 264 bits (24 x 11 bits): 256 bits for the seed and 8 bits for the checksum. In theory, you could pick 23 words at random with 11 * 23 coin flips, every 11 flips representing an index in the dictionary. Now to find which 24th word passes the checksum, you could guess it in at most 2048 attempts on your hardware wallet :) More realistically, it might be possible to develop a Ledger app that, given 23 words, finds the "checksum-passing" 24th word for you.
- TacticalCoder 4y ago
  > More realistically, it might be possible to develop a Ledger app that, given 23 words, finds the checksum passing 24th word for you. Ah that's an interesting thought: I don't know about other hardware wallets but indeed the Ledger allows anyone to develop "nano apps" and it doesn't seem crazy to write one that'd compute the checksum after you gave it the 23 words you got throwing dice (well, 23 words + the three first bits of the 24th word really). Maybe it even already exists?
  - olalonde 4y ago
    I couldn't find one. I'm tempted to give it a shot. I will comment here if I succeed :)
- whatisweb3 4y ago
  Yes, once you have 23 words, there is a finite set of possible words that can be used as the 24th to make checksum valid, and you could pick one at random. But as I understand the private key can be any number, so you do not need to even use the seed phrase technique to create a private key, or if you do it isn’t required that it has a valid checksum in order to operate on the network.
  - olalonde 4y ago
    That's true but I think the idea was to generate a passphrase that can subsequently be entered into a hardware wallet. And most hardware wallets only support entering seed phrases with a valid checksum.
yencabulator 4y ago
> no HDD, booted from, say, a live Linux CD I so wish there was a USB stick on the market where you can toggle read-only mode with a physical switch. (And where you had reasonable confidence that the firmware is hard to attack, I guess.)

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olalonde 4y ago

> You can do that but you'll need a way to generate the checksum for the seed phrase. A 24 words BIP39 seed contains 264 bits (24 x 11 bits): 256 bits for the seed and 8 bits for the checksum. In theory, you could pick 23 words at random with 11 * 23 coin flips, every 11 flips representing an index in the dictionary. Now to find which 24th word passes the checksum, you could guess it in at most 2048 attempts on your hardware wallet :) More realistically, it might be possible to develop a Ledger app that, given 23 words, finds the "checksum-passing" 24th word for you.

TacticalCoder 4y ago
> More realistically, it might be possible to develop a Ledger app that, given 23 words, finds the checksum passing 24th word for you. Ah that's an interesting thought: I don't know about other hardware wallets but indeed the Ledger allows anyone to develop "nano apps" and it doesn't seem crazy to write one that'd compute the checksum after you gave it the 23 words you got throwing dice (well, 23 words + the three first bits of the 24th word really). Maybe it even already exists?
- olalonde 4y ago
  I couldn't find one. I'm tempted to give it a shot. I will comment here if I succeed :)
whatisweb3 4y ago
Yes, once you have 23 words, there is a finite set of possible words that can be used as the 24th to make checksum valid, and you could pick one at random. But as I understand the private key can be any number, so you do not need to even use the seed phrase technique to create a private key, or if you do it isn’t required that it has a valid checksum in order to operate on the network.
- olalonde 4y ago
  That's true but I think the idea was to generate a passphrase that can subsequently be entered into a hardware wallet. And most hardware wallets only support entering seed phrases with a valid checksum.

yencabulator 4y ago

> no HDD, booted from, say, a live Linux CD I so wish there was a USB stick on the market where you can toggle read-only mode with a physical switch. (And where you had reasonable confidence that the firmware is hard to attack, I guess.)