This could could be a viable option. I think this is the right approach.

Any downside to this and how much does this add to the blockweight if anything at all.

Anonymouse

> On Jan 22, 2019, at 4:19 AM, ZmnSCPxj via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
>
> Good Morning Matt,
>
>> ### ZmnSCPxj,
>>
>> I'm intrigued by this mechanism of using fixed R values to prevent multiple signatures, but how do we derive the R values in a way where they are
> unique for each blockheight but still can be used to create signatures or verify?
>
> One possibility is to derive `R` using standard hierarchical derivation.
> Then require that the staking pubkey be revealed to the sidechain network as actually being `staking_pubkey = P + hash(P || parent_R) * G` (possibly with some trivial protection against Taproot).
> To sign for a blockheight `h`, you must use your public key `P` and the specific `R` we get from hierarchical derivation from `parent_R` and the blockheight as index.
>
>
>
> Regards,
> ZmnSCPxj
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