[EPIC] Rollkit Light Client

[tzdybal]

This is a tracking issue for creating Optimint Light Client.

Light client functionality depends on availability of SMT in cosmos-sdk, so we're blocked on https://github.com/celestiaorg/optimint/issues/358.

Technical requirements for optimint light clients:

• full node must be able to generate proofs
• full node must be able to gossip fraud proofs
• light node must be able to receive and gossip fraud proofs
• light node must be able to validate fraud proofs
• changes to data structures:
  • intermediate state roots for DeliverTxs should be included in block body; committed in header
  • intermediate state roots for BeginBlock and EndBlock can be included in header
• SMT-based multi-commit store is required for effective generation and validation of Fraud Proofs in cosmos-sdk
• customized multi-commit store is required for generation of intermediate state roots (ISRs)
• changes to ABCI are required
  • ResponseBeginBlock, ResponseEndBlock and ResponseDeliverTx need to contain intermediate state root
  • note: state root in ResponseEndBlock should be the same as the one reported by ResponseCommit.
  • there needs to be a way to trigger fraud proof generation; we discussed two options:
    • optimint compares expected ISR and actual ISR returned by cosmos-sdk/app, and triggers fraud proof generation
      • IMHO it's cleaner design from high level perspective
    • optimint passes expected ISR; cosmos-sdk/app compares it with actual ISR; if they are different it returns fraud proof
  • fraud proof data type needs to be defined
• ADR-007 - commitment do data in headers aka "headers as footers"

---

• [x] #526
• [ ] Configuration option to enable light client mode
• [ ] Light client mode
  • [ ] Disable mempool
  • [ ] Disable block sync
• [ ] Celestia-node header sync
  • [x] #541
  • [x] #540
  • [x] #542
• [ ] TX inclusion proof generation (full node)
• [ ] TX inclusion proof verification (light node)
• [ ] Changes in full node
  • [ ] Separate header and block sync
  • [ ] TX inclusion proof generation
• [ ] Changes in light node
  • [ ] Forward queries to trusted nodes
  • [ ] Disable TX gossiping
• [x] #642

[liamsi]

related:

• https://github.com/celestiaorg/optimint/issues/36
• https://github.com/celestiaorg/optimint/issues/87

The light client also will need to understand how leader selection works btw.

[jbowen93]

Related Notion doc: https://www.notion.so/celestiaorg/Light-client-520b89c50d8b4eb489a0e4fcc3798ed9

[jbowen93]

Thanks for the great summary Tomasz. I'm going to make sub issues for all of this.