Subject: Re: [bitcoin-dev] Bitcoin vaults with anti-theft recovery/clawback mechanisms

From: Sergio Demian Lerner <[email-masked]>
Date: Wed, 7 Aug 2019 23:09:20 -0300

Seems to be comparable to the proposed "Tick Method" from 2013:
https://bitcointalk.org/index.php?topic=307211.msg3308565#msg3308565

However I remember that someone told me the tick method had a flaw..

On Wed, Aug 7, 2019 at 6:28 PM Dustin Dettmer via bitcoin-dev <
[email-masked]> wrote:

> Does revaulting vault up with the same keys, or new ones?
>
> Are they new derivation paths on the same key?
>
> Would love some expanded explanation on how you’re proposing this would
> work.
>
> Thanks,
> Dustin
>
> On Wed, Aug 7, 2019 at 1:35 PM Bryan Bishop via bitcoin-dev <
> [email-masked]> wrote:
>
>> Hi,
>>
>> One of the biggest problems with the vault scheme (besides all of the
>> setup data that has to be stored for a long time) is an attacker that
>> silently steals the hot wallet private key and waits for the vault's
>> owner to make a delayed-spend transaction to initiate a withdrawal
>> from the vault. If the user was unaware of the theft of the key, then
>> the attacker could steal the funds after the delay period.
>>
>> To mitigate this, it is important to choose a stipend or withdrawal
>> amount per withdrawal period like x% of the funds. This limits the
>> total stolen funds to x% because once the funds are stolen the user
>> would know their hot key is compromised, and the user would know to
>> instead use one of the other clawback paths during all of the future
>> withdrawal delay periods instead of letting the delay timeout all the
>> way to the (stolen) default/hot key.
>>
>> The reason why a loss limiter is the way to go is because there's
>> currently no way (that I am aware of, without an upgrade) to force an
>> attacker to reveal his key on the blockchain while also forcing the
>> attacker to use a timelock before the key can spend the coins. I am
>> curious about what the smallest least invasive soft-fork would be for
>> enabling this kind of timelock. There are so many covenant proposals
>> at this point (CHECKSIGFROMSTACK, SECURETHEBAG, CHECKOUTPUTVERIFY,
>> ....). Or there's crazy things like a fork that enables a transaction
>> mode where the (timelock...) script of the first output is
>> automatically prefixed to any of the other scripts on any of the other
>> outputs when an input tries to spend in the future. A thief could add
>> his key to a new output on the transaction and try to spend (just like
>> a user would with a fresh/rotated key), but the OP_CSV would be
>> automatically added to his script to implement the public observation
>> delay window.
>>
>> Also, there was other previous work that I was only informed about
>> today after posting my proposal, so I should mention these as related
>> work:
>>
>> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-February/015793.html
>>
>> https://blog.oleganza.com/post/163955782228/how-segwit-makes-security-better
>> https://www.youtube.com/watch?v=diNxp3ZTquo
>> https://bitcointalk.org/index.php?topic=5111656
>>
>> - Bryan
>> http://heybryan.org/
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