Intershard Signalling Mechanism

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Sharding not only helps overcome scalability issues. Intershard signaling allows transactions between shards and communication of smart contracts on different shards.

Concordium's sharding protocol for this operates as follows :

When a block finalizes on a shard, it contains a list of outgoing messages for other shards. The nodes of the sending shard sign the list of outgoing messages.

The nodes in the receiving shard can obtain the list of nodes running on the sending shard together with their public keys from the control chain, which allows them to verify the signed messages from the sending shard.

Once a message is verified, it is executed on the receiving shard.