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Q. Interoperability of different DID/DIF ecosystems ...
A. Discussion
Q. What are the main challenges for integrating/interoperating different types of signatures?
A. Each blockchain platform has a different algorithm to create keys: The main idea, everything is verified in chaincode or smart contracts, we only need to verify.
Q. Sharded keys / multiple keys?
A. We didn't have time for this requirement (so far).