Subject: Re: [bitcoin-dev] Satoshilabs secret shared private key scheme

From: Peter Todd <[email-masked]>
Date: Mon, 8 Jan 2018 19:37:25 -0500

On Tue, Jan 09, 2018 at 09:26:17AM +1100, Ben Kloester wrote:
> > This sounds very dangerous. As Gregory Maxwell pointed out, the key
> derivation
> > function is weak enough that passphrases could be easily brute forced
> 
> So you are essentially imagining that a perpetrator will combine the
> crypto-nerd fantasy (brute forcing the passphrase) *with* the 5-dollar
> wrench attack, merging both panes of Randall Munroe's comic? Seems
> vanishingly unlikely to me - attackers are generally either the wrench
> type, or the crypto-nerd type.

We're talking about seeds here, not hardware wallets.

For a hardware wallet theft scenario, if you're worried about muggers you can
make the hardware have secret accounts with different seeds, *without* risking
user funds getting lost - a much more likely scenario - due to mistyped
passwords.

In any case, even if you were to do this type of design, a much better idea is
to use a checksum by default to reject invalid passwords, while having an
advanced-use-only option to override that checksum. The virtual file encryption
filesystem encfs does exactly this with its --anykey flag. This allows advanced
users to do their thing, while protecting the majority of users for whome this
feature is dangerous.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org