Citrea live on Bitcoin mainnetCitrea live on Bitcoin mainnet

well, if you thought hArk was complicated (#1420646), get a load of Citrea:

Citrea is a rollup. It regularly submits batch proofs to Bitcoin - which also include the state differences for each batch, meaning that any changes from the start to the end of a batch are also available for anyone reading Bitcoin.

A Citrea full node can read the state differences and reconstruct the state directly from Bitcoin - unlike sidechains, in which only small cryptographic commitments are posted and it is impossible to reconstruct the state using that data.

Citrea uses Bitcoin as a Data Availability layer, and it's the only source of truth for the system. As long as Bitcoin is secure, the state of Citrea will be accessible and reconstructable.

I take this to mean you can do a bunch of stuff in a database and then pack up the state into a bitcoin transaction and save as. This is probably a crude interpretation of what's going on, but I'm a bit rough around the edges, so there you go.

You can start doing complicated things with citrea using any of the usual shitcoin wallets: Metamask, Base, Rainbow, Brave wallet, and so on.

Just go to: app.citrea.xyz

What's the point of a database that saves data in bitcoin transactions?What's the point of a database that saves data in bitcoin transactions?

Now, imagine you want to use sats in this database. Sats only exist in bitcoin transactions (hmm, I wonder if this is actually true), so to use sats in Citrea, you have to send sats to some multisig (this is called a bridge) and then the signers in charge of the multisig vouch for you and credit you citrea-sats (they call this cBTC) in the database. They call their multisig thing Clementine.

Existing Bitcoin bridges usually depend on trusted multisigs or on separate chains/consensus, pushing users to accept an honest‑majority assumption and moving economic activity away from Bitcoin.

Clementine is a trust-minimized solution based on BitVM2 - a new breakthrough that enables optimistic verification of ZK Proofs directly on Bitcoin without any changes / soft-forks.

Using BitVM2, one can:
verify the correctness of a ZK Proof on Bitcoin
and, in case a provided proof is not correct, can determine and take action against it on Bitcoin.
With the help of BitVM2 Clementine keeps the safety of funds on Bitcoin, reduces the peg-out trust to “1‑of‑N honesty”, and achieves trust-minimization:
One honest Signer ensures funds can only follow pre‑approved spend paths.
One honest Watchtower can block a claim anchored to the wrong Bitcoin chain.
One rational Challenger can prove an invalid computation and seize a malicious Operator’s collateral.
As long as 1-of-N honest assumption holds, funds are protected against both liveness failures and theft.

Clementine whitepaper and codebase.

This really only leaves one question...

But is there a stablecoin?But is there a stablecoin?

Oh yes, there is.

Not wanting to miss out on the stablecoin bonanza, Citrea has created a new stablecoin - ctUSD.

Now that we live in the GENIUS world, we know that stablecoins issued in the US need to be issued by a licensed entity -- in ctUSD's case this is moonpay. Moonpay has all the licenses.

ctUSD is a 1:1 U.S dollar-denominated stablecoin, fully backed by short-term U.S. Treasury bills and cash. Powered by M0, the universal stablecoin platform, ctUSD is issued by MoonPay, the global leader in crypto payments with a rigorous compliance framework built on the highest U.S. standards. This partnership ensures ctUSD is designed to align with the forthcoming GENIUS Act guidelines and an asset available to users in the U.S. (excluding NY) and over 160 countries worldwide (excluding Canada and the EEA).

You may recall that Flashnet and Spark have their own little stablecoin called USDB, which was issued by a stablecoin as a service company called Brale (#1416125). Well, it seems that Brale is not the only company getting in on this business.

I have never heard of M0 before.

I don't really have any sense of why Citrea needs M0 to help them with ctUSD on Citrea (which is on Bitcoin) when Moonpay is the issuer of the stablecoin, but this construction reminds me a little of the Spark-Flashnet-Brale setup, so perhaps it's just the way these things are done.

Citrea posts this helpful chart on their ctUSD announcement page:

So now that that's all cleared up, look at all the cool things you can do on Citrea: