Open HRMP Channel Between Karura and Listen


We propose to open HRMP communication between Listen and Karura. This will require a few actions from the governance bodies of both chains.


We propose to open a bi-directional channel between Karura and Listen. The two primary use cases will be:

  1. To transfer Karura’s assets to Listen so they can be privatized and transferred confidentially and anonymously.
  2. Listen’s LT token can be transferred to Karura to open new DEX pairs and integrate with Karura’s suite of DeFi products.


There is no on-chain proposal yet; #LT.

Technical details:

The procedure for opening the channels is as follows:

  1. Listen initializes a proposal to open Listen to Karura HRMP channel via [Listen Governance].
  2. Wait until the proposal on step 1 gets approved & enacted.
  3. Karura proposes to accept the Listen to Karura HRMP channel and open a Karura to Listen HRMP channel via [Karura Governance Batch call].
  4. Wait until the proposal on step 3 gets approved & enacted.
  5. Listen proposes to accept the Karura to Listen HRMP channel via [Listen Governance].
  6. Wait until the proposal on step 6 gets approved & enacted.
  7. Wait for another session on Kusama for the change to be effective.
  8. Listen proposes to register Karura’s assets via [Listen Governance].
  9. Karura proposes to register Listen’s asset via [Karura Governance].
  10. Wait until both proposals on step 9 & 10 are approved & enacted.
  11. XCM based crosschain transfer will be possible at this stage.

The extrinsics that need to be sent with xcm messages to they can be executed on the relay chain , are:

  • For step 1:
    hrmp.hrmpInitOpenChannel(recipient: 2000, proposedMaxCapacity: 1000, proposedMaxMessageSize: 102400) , which hex-encoded is 0x3c00d0070000e803000000900100
  • For step 3:
    The first call is hrmp.hrmpAcceptOpenChannel(sender: 2118) , second call is hrmp.hrmpInitOpenChannel(recipient: 2118, proposedMaxCapacity: 1000, proposedMaxMessageSize: 102400) , so the final batch call hex-encoded is 0x3c0046080000e803000000900100
  • For step 5: hrmp.hrmpAcceptOpenChannel(sender: 2000) , which hex-encoded is 0x3c01d0070000

The proposedMaxCapacity and proposedMaxMessageSize are set to the values of Kusama’s configuration.activeConfig.hrmpChannelMaxCapacity and configuration.activeConfig.hrmpChannelMaxMessageSize values, respectively.

These extrinsics need to be called with the parachain’s sovereign account as origin. To achieve this, on the Listen side we will use polkadot-xcm pallet to send xcm message to the relaychain, by executing the following extrinsic from the parachain. Karura should make an open request call and an accept request call with its orml-xcm pallet.

As a prerequisite, the parachain’s sovereign account must contain at least 10 KSM to be locked as collateral (5 for each channel direction), plus some KSM to pay for xcm execution fees.

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