When I see more and more proposals like this, where things are commited to 
Taproot outputs, then I think we should start designing "miner-based 
commitments". If someone is going to make a Bitcoin transaction and add a 
commitment for zero cost, just by tweaking some Taproot public key, then it is 
a benefit for the network, because then it is possible to get more things with 
no additional bytes. Instead of doing "transaction-only", people can do 
"transaction+commitment" for the same cost, that use case is positive.

But if someone is going to make a Bitcoin transaction only to commit things, 
where in other case that person would make no transaction at all, then I think 
we should have some mechanism for "miner-based commitments" that would allow 
making commitments in a standardized way. We always have one coinbase 
transaction for each block, it is consensus rule. So, by tweaking single public 
key in the coinbase transaction, it is possible to fit all commitments in one 
tweaked key, and even make it logarithmic by forming a tree of commitments.

I think we cannot control user-based commitments, but maybe we should 
standardize miner-based commitments, for example to have a sorted merkle tree 
of commitments. Then, it would be possible to check if some commitment is a 
part of that tree or not (if it is always sorted, then it is present at some 
specified position or not, so by forming SPV-proof we can quickly prove, if 
some commitment is or is not a part of some miner Taproot commitment).

On 2022-04-05 15:06:03 user Olaoluwa Osuntokun <laol...@gmail.com> wrote:

Hi y'all,

I'm excited to publicly publish a new protocol I've been working on over the 
past few months: Taro. Taro is a Taproot Asset Representation Overlay which 
allows the issuance of normal and also collectible assets on the main Bitcoin 
chain. Taro uses the Taproot script tree to commit extra asset structured meta 
data based on a hybrid merkle tree I call a Merkle Sum Sparse Merkle Tree or 
MS-SMT. An MS-SMT combined the properties of a merkle sum tree, with a sparse 
merkle tree, enabling things like easily verifiable asset supply proofs and 
also efficient proofs of non existence (eg: you prove to me you're no longer 
committing to the 1-of-1 holographic beefzard card during our swap). Taro asset 
transfers are then embedded in a virtual/overlay transaction graph which uses a 
chain of asset witnesses to provably track the transfer of assets across 
taproot outputs. Taro also has a scripting system, which allows for 
programmatic unlocking/transfer of assets. In the first version, the scripting 
 system is actually a recursive instance of the Bitcoin Script Taproot VM, 
meaning anything that can be expressed in the latest version of Script can be 
expressed in the Taro scripting system. Future versions of the scripting system 
can introduce new functionality on the Taro layer, like covenants or other 
updates.

The Taro design also supports integration with the Lightning Network (BOLTs) as 
the scripting system can be used to emulate the existing HTLC structure, which 
allows for multi-hop transfers of Taro assets. Rather than modify the internal 
network, the protocol proposes to instead only recognize "assets at the edges", 
which means that only the sender+receiver actually need to know about and 
validate the assets. This deployment route means that we don't need to build up 
an entirely new network and liquidity for each asset. Instead, all asset 
transfers will utilize the Bitcoin backbone of the Lightning Network, which 
means that the internal routers just see Bitcoin transfers as normal, and don't 
even know about assets at the edges. As a result, increased demand for 
transfers of these assets as the edges (say like a USD stablecoin), which in 
will turn generate increased demand of LN capacity, result in more transfers, 
and also more routing revenue for the Bitcoin backbone nodes.

The set of BIPs are a multi-part suite, with the following breakdown:
 * The main Taro protocol: 
https://github.com/Roasbeef/bips/blob/bip-taro/bip-taro.mediawiki
 * The MS-SMT structure: 
https://github.com/Roasbeef/bips/blob/bip-taro/bip-taro-ms-smt.mediawiki
 * The Taro VM: 
https://github.com/Roasbeef/bips/blob/bip-taro/bip-taro-vm.mediawiki
 * The Taro address format: 
https://github.com/Roasbeef/bips/blob/bip-taro/bip-taro-addr.mediawiki
 * The Taro Universe concept: 
https://github.com/Roasbeef/bips/blob/bip-taro/bip-taro-universe.mediawiki
 * The Taro flat file proof format: 
https://github.com/Roasbeef/bips/blob/bip-taro/bip-taro-proof-file.mediawiki

Rather than post them all in line (as the text wouldn't fit in the allowed size 
limit), all the BIPs can be found above.

-- Laolu

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