Open HRMP cross-chain communication between Litmus and Karura

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

Summary

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

  1. To transfer Karura’s assets to Litmus so they can be privatized and transferred confidentially and anonymously. (TBA)
  2. Ltimus LIT token can be transferred to Karura to open new DEX pairs and integrate with Karura’s suite of DeFi products.

Proposal

HRMP channel established; #TBD.

Technical details:

The procedure for opening the channels is as follows:

  1. Litmus initializes a proposal to open Litmus to Karura HRMP channel via [Litmus Governance].
  2. Wait until the proposal on step 1 gets approved & enacted.
  3. Karura proposes to accept the Litmus to Karura HRMP channel and open a Karura to Litmus HRMP channel via [Karura Governance Batch call].
  4. Wait until the proposal on step 3 gets approved & enacted.
  5. Ltimus proposes to accept the Karura to Litmus HRMP channel via [Litmus 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. Ltimus proposes to register Karura’s assets (Acala does this on Litmus’s behalf).
  9. Wait until both proposals on step 9 & 10 are approved & enacted.
  10. 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: 2106) , second call is hrmp.hrmpInitOpenChannel(recipient: 2106, proposedMaxCapacity: 1000, proposedMaxMessageSize: 102400)
  • 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 Litmus 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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