# A-Z of Hyperlane
gm gm gm!!!
Even with the vast network of blockchain, with 1000s of nodes and 100s of chains (L1, L2, L3....) the users are getting restricted in utilizing the complete potential of the decentralized network. Reason? Some application works on ETH, some on Polygon, some on Gnosis, and so on and on!
In the ever-growing network of Blockchain Networks, or ***different blockchain networks*** developers are required to build chain-agnostic applications.
> *No dependency on one chain, and no restriction for any user.*
Now solving this interoperability issue between different chains requires devs to build robust and more importantly secure designs, which is a highly technical and resourceful process, and to save devs from going through such pain [**Hyperlane**](https://www.hyperlane.xyz) comes into the picture.
In this article, we are going to learn almost all about Hyperlane and it works, so grab a coffee βοΈ and LFG π
---
# What is Hyperlane?
**Hyperlane is a Permissionless Interoperability Protocol** that helps devs send arbitrary data across chainsβ
> Read in short here:
>
> %[https://twitter.com/megabyte0x/status/1686628441888804864]
**"Permissionless"** means *no one requires any sort of permission* from the Hyperlane Team to use Hyperlane SDK, Contracts, or even while deploying on new chains as I didππ»
%[https://twitter.com/megabyte0x/status/1651938319570456577]
**"Interoperability"** means *sending between different chains*. Imagine initiating a transaction on ETH on certain to close a position on Polygon.
Hyperlane is a **complete modular protocol** that helps devs to customize it according to their application requirements.
The following are the key components of Hyperlane:
* Mailbox
* Interchain Security Module \[ISM\]
* Interchain Gas Payment \[IGP\]
* Agents
> You can either learn about all of them in deep one by one or go directly to the last section for a quick view with examples.
# Mailbox
***Mailbox is an on-chain API to send and receive interchain messages.***
> You can also check this out:
>
> %[https://twitter.com/megabyte0x/status/1686979539291762688]
Mailbox is the middle-man \[but CODE\] which helps devs to connect between different chains and leverage it to build something out of the box.
Their contracts are required to be present on every [chain supported by Hyperlane.](https://docs.hyperlane.xyz/docs/resources/addresses)
Mailbox Interface has two functions that are required to be present in the cross-chain contracts, those are the following:
* `dispatch`
* `process`
## dispatch
This is used to send the data from the origin chain to the destination chain.
It accepts several params:
![](https://cdn.hashnode.com/res/hashnode/image/upload/v1693564023609/bc6ce931-e81f-49df-80a3-e962ee166066.png align="center")
* `_destinationDomain (uint32)`: domain for the destination chain as per the Hyperlane Docs or the deployer.
* `_recipient Address (bytes32)`: address of the recipient.
* `_messageBody (bytes)`: Raw bytes content of message body
It works by following these steps:
![](https://cdn.hashnode.com/res/hashnode/image/upload/v1693564190795/f026d50f-6fe4-43d5-bdf6-070f91c4f8ac.png align="center")
* First, check whether the message length exceeds the 2KiB length.
* It formats the \_`messageBody` using [Message.sol](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/libs/Message.sol) according to the needs.
* [Message.sol](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/libs/Message.sol) provides a function `.id()` that returns keccak256(\_message). This \_id is saved into the ["incremental" Merkle Tree.](https://medium.com/@josephdelong/ethereum-2-0-deposit-merkle-tree-13ec8404ca4f)
* The Merkle Tree is used to verify fraud proofs in Hyperlane's Staking and Slashing Protocol.
## process
This is used on the destination chain to receive the message.
It accepts the following two params:
![](https://cdn.hashnode.com/res/hashnode/image/upload/v1693564279003/2b1971f7-4392-4c37-8af9-5b7aa9374df9.png align="center")
It works by following these steps:
![](https://cdn.hashnode.com/res/hashnode/image/upload/v1693593889185/09afb654-cf53-4afd-9fb4-8c843424fa5e.png align="center")
* `_message` is the formatted message from the [Message.sol](https://github.com/hyperlane-xyz/hyperlane-monorepo/blob/main/solidity/contracts/libs/Message.sol)
* `_metadata` is the specific Arbitrary metadata provided by the relayer used by [ISM](https://docs.hyperlane.xyz/docs/protocol/sovereign-consensus) to verify `_message`
* Then it checks whether this `_id` is in the array of delivered messages or not. If it is, then it reverts with **"delivered"** else add it to the array of delivered messages.
* Then it gets the ISM Address for the `recepientAddress`.
* If the recipient has defined a specific ISM it returns that else uses the default ISM for the chain.
* It uses the ISM address to verify messages received by the Mailbox.
* After all verification, it emits the message received event using the `IMessageRecepient.sol`
> Learn more about Mailbox [here](https://docs.hyperlane.xyz/docs/protocol/messaging).
# Interchain Security Modules
**ISM verifies the particular messages delivered on the destination chain are *actually* sent from the origin chain.**
> You can also check this out:
>
> %[https://twitter.com/megabyte0x/status/1687471625724383232]
ISM is used in the Mailbox, to verify the message Mailbox received from the relayer before executing txns.
Developers can define specific ISM for their applications or can use pre-built ISMs provided by the team, using the `ISpecifiesInterchainSecurityModule.sol`
ISMs are:
![Image](https://pbs.twimg.com/media/F2sYYrcbsAA_Zii?format=png&name=900x900 align="left")
Configurable
ISM can be configured as per the application requirements, with all the additional parameters required by the application.
Composable
Devs can use more than one ISM in their application to increase security and work according to the consensus of the chain.
Customizable
Devs can use IInterfaceSecurityModule.sol and can build the whole ISM according to their needs.