Pairwise Bridges
Cross-chain bridges such as wrapped assets enable a crypto asset owned by a party to be burned/locked on one chain while an identical asset is minted/unlocked on another network. The minted asset is then sent to an address owned by the original user. tBTC is an example of a customized protocol that combines smart contracts and collaterals to secure token transfers between Bitcoin and Ethereum Blockchains.
Pairwise bridges require significant engineering efforts to create. For example, for each chain pair, developers must build a new smart contract on both chains to prove the validity of the chains’ state. Besides substantial efforts, pairwise bridges cannot scale when one of the underlying chains upgrades its consensus protocol or transaction format. This is because developers would need to upgrade the logic of smart contracts operating the chain pairs.
We have also seen a few other iterations of single-purpose bridges that attempt to rewrite state transition logic in smart contracts. These solutions suffer from scalability and security issues like oracles, sidechains, and pairwise bridges.
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