> For the complete documentation index, see [llms.txt](https://crosschain-alliance.gitbook.io/hashi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://crosschain-alliance.gitbook.io/hashi/core-concepts/block-header-relaying.md).

# Block Header Relaying

Block headers are at the heart of Hashi’s security model. Rather than just relying on arbitrary messages between chains, Hashi works by relaying entire block headers from one blockchain to another. This means that dApps can verify not only the content of a message but the actual state of the originating chain.

* **Why Block Headers?**\
  Block headers contain essential information about the state of a blockchain, including the hash of the previous block, timestamp, and the Merkle root of all transactions. By relaying these, Hashi ensures that cross-chain interactions are based on cryptographic proofs tied to actual blockchain states, making them much more secure than simple message relays.
* **How Hashi Uses Block Headers**\
  Multiple independent oracles relay these block headers, which are then aggregated and validated by Hashi. The result is a robust verification process where only confirmed, valid block headers are accepted, ensuring data integrity across chains.


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