## sMPC Interoperability (DCRM)

Perhaps the toughest challenge in Blockchain technology has been the challenge of interoperability and how it can be made just as trust-less as blockchain itself. DCRM (Distributed Control Rights Management) is the name of Fusion's sMPC protocol and has been verified and audited by cryptographers Rossario Gennaro ,Steven Goldfeder, Louis Gobin and Pascal Paillier in order to make certain that it's as secure as can be. A first step to achieving such trust. But the interoperability journey for Fusion is far from over and many things have changed from the original HHCM promise in the white paper.

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sMPC stands for Secure Multi Party Computation and basically means that many different nodes can together calculate a cryptographic signature, in a situation where they individually don't know the private key. In a way, you can say that the basic use of sMPC is a Multisig Wallet. And SMPCWallet is the DCRM version of this basic use case. What this means is that more than one person (and node) is needed to control contents of the wallet. Exactly how many are needed is decided by something called TSS (threshold signature scheme). TSS consists of two numbers n/t, where n is the number of nodes needed to complete a signature and t is the total number of nodes that are part of the scheme.

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This basic version of TSS only works in a PoA situation, where the total number of nodes (t) is known and set. A more advanced scheme can allow which nodes that are considered part of "t" to be changing, and an even more advanced scheme could allow the numbers "n" and "t" to grow or diminish, depending on how many nodes wish to be part of the scheme.

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For DCRM to be fully integrated into an anonymous Proof of Stake consensus such as Fusion it would be needed for any node to enter and exit the scheme and the scheme to be self-adjusting according to current circumstances. This would be quite advanced and does as of yet not exist.

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For now a relatively transparent version of DCRM exists on the Multichain Router, whose nodes can be viewed here. This implementation is used to achieve interoperability between blockchains. The nodes govern a set of bridges which mint tokens on the desired blockchain after locking in the same amount of tokens on the original chain.

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Another version that's more relavent directly for Fusion is the DCRM alliance implementation which is utlized by Chainge.

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For Fusion this implementation means that many, many coins and tokens can exist on the Fusion network as universal assets and that FSN can be moved onto a large number of other networks. Thus every goal of interoperability is already possible, but the security of the implementation can still be improved and many still hope that it can one day be governed natively by Fusion nodes. In the meantime Chainge use and size is in costant growth, as it's aiming to become a decentralized platform easy enough to use that it could replace centralized exchanges.

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One of the most impressive achievements when it comes to DCRM in terms of "official" recognition, was the fact that it was included in a report written by ECB.

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