Re: [bitcoin-dev] Storm: escrowed storage and messaging at L2/L3

[Stefan Richter <richter@cs.rwth-aachen.de>]

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Please see the github issues and the twitter discussion (e.g. here:
https://twitter.com/stefanwouldgo/status/1163801056423403520) for similar
points other people including me have made. At this point I feel there are
quite a few unclear points in the presentation and it is not clear to me if
they can be salvaged.

Am Mi., 21. Aug. 2019 um 09:32 Uhr schrieb ZmnSCPxj via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org>:

> Good morning Maxim,
>
> The Deaf Bob Attack
> ===================
>
> It seems to me that Bob can promote the N3 problem to the N2 problem.
>
> Suppose Alice contacts Bob to get the data.
> However, Bob happens to have lost the data in a tragic boating accident.
>
> Now, supposedly what Alice does in this case would be to broadcast the
> HTLC settlement transaction, whose signature was provided by Bob during
> protocol setup.
>
> But this seems unworkable.
>
> * If Bob managed to sign the HTLC settlement transaction, what `SIGHASH`
> flags did Bob sign with?
>   * If it was `SIGHASH_ALL` or `SIGHASH_SINGLE`, then Bob already selected
> the decryption key at setup time.
>   * If it was `SIGHASH_NONE`, then Alice could put any SCRIPT, including
> `<Alice> OP_CHECKSIG`.
>
> If Bob already selected the decryption key at setup time, then Bob can
> ignore Alice.
>
> * If Alice does not publish the HTLC settlement transaction, then Bob will
> eventually enter the N2 state and get the stake+reward.
> * If Alice *does* publish the HTLC settlement transaction, without Bob
> giving the encrypted data, then Bob can just use the hashlock and reveal
> the decryption key.
>   * The decryption key is useless without the encrypted data!
>
> It seems this part is not workable?
> As the decryption key is embedded in the HTLC, Alice cannot get a
> signature from Bob without the decryption key already being selected by Bob
> (and thus already claimable even without any data being returned by Bob).
>
>
> Regards,
> ZmnSCPxj
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