Hi Jeremy,

For Citrea/Clementine, we currently use SPV-style proofs in two main places.

First, on the Citrea side, the Bridge system contract uses Bitcoin 
transaction inclusion proofs to accept peg-ins/deposits. See:

<https://github.com/chainwayxyz/citrea/blob/487daa67fc54feb789b618a0ca2be1cc2f09b198/crates/evm/src/evm/system_contracts/src/Bridge.sol#L196>

The contract checks inclusion through Citrea's Bitcoin light client 
contract. More details here:

<https://docs.citrea.xyz/developer-documentation/system-contracts/bitcoin-light-client>

Second, in the Clementine Bridge proof, we use SPV proofs for verifying 
operator payout transactions. If an operator is challenged, the operator 
proves that there exists a payout transaction paying the withdrawal. See:

<https://github.com/chainwayxyz/clementine/blob/b711e92ef2725e8b3cdaacc2683583f11b5aec28/circuits-lib/src/bridge_circuit/spv.rs>

On your question about commitment structures, I think being able to verify 
that a particular coin was not spent in a block might be helpful, as it 
could make creating SNARK proofs for operator honesty easier in some bridge 
designs.

Best,
Ekrem BAL
On Thursday, May 14, 2026 at 10:47:59 AM UTC-4 jeremy wrote:

> Dear Bitcoin Developers,
>
> SPV proofs are an important part of Bitcoin's Design, after all Satoshi 
> thought they were worth including in the whitepaper!
>
> As far as I'm aware, they have somewhat limited usage in the wild, mainly 
> in Electrum and in Layer 2 Bridges, but it is important that they work 
> correctly.
>
> I'd like to gather a bit more detailed information on where and how SPV 
> proofs are currently used, as well as any other proposed uses of SPV proofs.
>
> In this Knowledge Gathering, I'd also like to glean a better understanding 
> of what types of commitment structures might work "better" than others for 
> SPV -- e.g., ability to cheaply verify if a block pays a particular 
> address, spends a particular coin, and the exclusion forms (does not pay an 
> address, does not spend a coin) etc, especially in the context of Layer 2 
> Bridging.
>
> Happy International Chihuahua Appreciation Day,
>
> Jeremy
>

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