Foundations of Blockchain

Cross-shard communication

There might be a scenario when a transaction needs to be shared between two or more shards. Ethereum uses receipts created by nodes in one shard to confirm the transaction. Let's consider a scenario in which user A present in shard M wants to send 100 coins to user B of shard N. Cross-shard communication can be established with the following steps:

1. Create a transaction on shard M for deducting the coins.

2. Create a receipt for the transaction of 100 coins from user A to B. The transaction won't be saved on the state, but the existence of the receipt can be verified by the users in shard N.

3. Create and send a transaction on shard N that includes the Merkle proof of the receipt. This transaction also confirms that ...