zk-rollup-module-for-Cosmos-SDK

This repository is for explaining objectives and technical description of how B-Harvest will implement zk-rollup module for Cosmos-SDK

Short Summary

zk-rollup methodology utilizing zk-SNARKs provide an efficient way to scale out from the Cosmos Hub (the Hub = Layer 1 = L1) to an application specific Cosmos Zone (a Zone = Layer 2 = L2) without sacrificing the security of the Hub.

In order to give the Hub ability to support any governance-allowed Zone with zk-rollup security enhancement, the Hub should adopt a generalized zk-rollup module which will provide zk-proof verification and merkle tree management functionality.

In this project, B-Harvest will provide "full zk-rollup package" to provide the community full development cycle to adopt additional zk-rollup supported Zone.

Background Technology

There exists multiple toolkits for zk-SNARKs. To name a few,

• https://github.com/scipr-lab/libsnark : C++
• https://github.com/zcash/zcash : C++
• https://github.com/barryWhiteHat/roll_up : C++
• https://github.com/zkcrypto/bellman : rust
• https://github.com/Zokrates/ZoKrates : rust
• https://github.com/matter-labs/zksync : rust
• https://github.com/Loopring/protocols : C++
• https://github.com/ConsenSys/gnark : golang

B-Harvest investigated many existing implementations and found out that the "gnark" implemented by Consensys is very concise, no library dependency, language compatible to Cosmos-SDK, performance optimized, and also providing relevant tools for simple usecase of zk-SNARKs and zk-rollup.

Not to re-invent the wheel, we will actively re-utilize many parts of gnark implementation to create entire zk-rollup package customized to Tendermint/Cosmos-SDK based blockchain usecase.

The gnark repository includes

• Groth16 implentation with
  • prover and verifier programs
  • ellptic curves : Edward twisted BN256, Edward twisted BLS381
  • merkle tree hash : MiMC
• Circuit programming tool
  • conversion system from constraint system (in golang) into R1CS
  • necessary circuit gadgets for elliptic curves and merkle tree hashing
  • pseudo zk-SNARKs setup script to output prover&verifier key

Range of Spec

Milestone 1 : Technology Package Delivery

Duration

• maximum 5 months

Backend

• zk-SNARKs tools for Cosmos ecosystem use-case

  • zk prover and verifier program
    • Groth16 implementation with default chosen elliptic curve and its pairing computation

• blockchain module

  • zk rollup module for the Hub
    • zk-proof verification and merkle tree management functionality
    • store current prover&verifier key
  • zk proof module for the Zone
    • zk-proof verification and merkle tree management functionality

• testcodes for each functionality provided

• detail backend process

  

  1. frontend : transaction broadcast

     • user create transaction on frontend
     • the transaction is broadcasted to L2 network

  2. L2 consensus : block commit with the transaction

     • proposer includes the transaction in a block
     • the block with the transaction is committed by L2 consensus
     • suggested merkle tree change is stored

  3. prover : read suggested merkle tree change on L2

  4. prover : calculate zk-proof

     • prover finds new suggested merkle tree change
     • zk-prover calculate zk-proof for the merkle tree change using predefined circuit program

  5. prover : transaction broadcasting

     • prover broadcasts zk-proof transaction
     • including merkle tree change and its zk-proof

  6. L2 consensus : block commit with the zk-proof

     • proposer includes the zk-proof transaction in a block
     • L2 consensus verifies the consistency of zk-proof
     • the block with the zk-proof transaction is committed by L2 consensus

  7. IBC relayer : relays committed zk-proof from L2 to L1

  8. L1 consensus : verify zk-proof

     • L1 consensus receives zk-proof relayed by IBC relayer
     • L1 consensus verify the received zk-proof

  9. L1 consensus : update merkle tree

     • L1 apply merkle tree change which is verified by zk-proof
     • updated merkle tree is committed on L1

  10. IBC relayer : relays updated merkle tree from L1 to L2

  11. L2 consensus : update merkle tree

      • L2 consensus updates merkle tree via relayed merkle tree from L1

Frontend and Tools

• zk tools
  • zk-SNARKs setup script for customized Cosmos usecase
• circuit programming gadgets
  • circuit program for signature verification with default chosen elliptic curve
  • circuit program for hash verification with default chosen merkle tree
  • example circuit program for plain vanilla ledger merkle tree with transfer utility and signature verification ability

Documentation, Marketing and Governance Effort

• Technology documentation describing the structure of whole package and list of related crypto technology employed and its mathematical security characteristics
• zk-rollup Explainer documentation and marketing contents for broader non-technical community members
• Various community engagement regarding spreading out benefits of zk-rollup on the Hub
• Related governance leadership to include zk-rollup module on the Hub

Milestone 2 : Governance Process and Production Support

Duration

• Maximum 3 months

Backend

• Governance Process
  • Process for add new zk-rollup supported Zone or Zone upgrade process
    • update prover&verifier key and reset merkle tree to genesis state of the Zone via governance procedure
    • the Hub does not need any software upgrade

Example Codes and Test Suite

• Example Daemons for plain vanilla Zone and related zk-rollup functionality
  • Customized IBC relayer daemon for communication between the Hub and the Zone
  • Prover daemon
    • listen from the Zone's LCD
    • calculate zk-proof for committed blocks on the Zone blockchain
    • broadcast zk-proof transaction onto the Zone blockchain
  • Node client daemon for the Zone
    • merkle tree management for zk-proof
    • zk-proof verification and storage into kv-store
  • Basic web interface for monitoring and testing entire zk-rollup process

Audit(not confirmative)

• Entire Package Audit by gnark Author : Gautam Botrel

Documentation and Simulation Report

• Additional Documentations
  • detail documentation to explain each step to deploy zk-rollup supported Zone on the Hub or other Cosmos blockchains
  • documentation about steps for entire flow testing
• Simulation Report
  • Performance zk-rollup test result with default vanilla Zone
    • prover&verifier performance with thousands of transaction in a block

Further Roadmap not Included in this Funding Project

• Privacy-preserving Zone with zk-rollup support from the Hub
• Performance optimization of zk prover
  • Parallel computing algorithm
  • Adopting alternative elliptic curves
  • Adopting alternative zk-SNARKs methodology
• Support signature verification functionality for multiple additional elliptic curves

Team Due Diligence / Track Record

Prior ICF funding history

• Four pillars for validator operation
  • Double-singing risk reduction (PR ready)
  • Improving trusted peering (Merged)
  • Tendermint mode (PR ready)
  • Validator consensus key rotation (under development)

Strong Motivation and Sustainable Management

• B-Harvest will implement zk-rollup supported Cosmos zone which will provide superior performance to users without sacrificing Hub-level security or congestion of the Hub with many related transactions. For this roadmap, generalized zk-rollup functionality of the Hub is the most crucial step. So, we are not only motivated but we naturally have strong incentives to provide zk-rollup module with best quality for our project.
• zk-rollup supported Cosmos zone roadmap also gives us synergetic reasons why we want to keep managing and improving the zk-rollup package. We hope to keep spreading the advantages of zk-rollup technology in Cosmos ecosystem and become a helpful guide to introduce and provide the functionality and tools.
• We have strong willingness to accept additional funding from ICF or community fund to extend our contribution to zk-rollup package by implementing further roadmap topics so that our module can keep track with global zk-rollup frontiers.

Skills and Man power

• Experience on Tendermint and Cosmos-SDK
  • Four pillars for validator operation
  • Kava audit
  • Terra grant for oracle vulnerability
• Crypto SDK implemented for advanced encryption schemes
  • secret sharing, proxy re-encryption, AEAD, KEM
• Man power
  • Mathematics expert for advanced elliptic curve utilization
    • Hyung(BS.math), Dokyung(PhD.math)
  • Tendermint/Cosmos-SDK specialists
    • Dongsam(MS.computer science), Jeseon(MS.computer science)
  • expert crypto engineer
    • Hanjun(BS.computer science)

Testability and Open source

• Testing
  • Testing consistency of zk-SNARKs process by testcodes
  • Guidelines and automated testing scripts for entire process
• Open source
  • The repository on github will be open source from begining

Budget

Man power

• Hyung(Full-time) : spec design, mathematics and cryptography verification, documentation, marketing and communication
• Dongsam(Full-time) : zk-rollup module development, governance module update
• Jeseon(Full-time) : building tools for zk processes and testing
• Hanjun(Full-time) : building cryptographic library for zk processes
• Dokyung(Part-time) : mathematics and cryptography verification

Budget

• Monthly budget
  • Full-time : $10K
  • Part-time
    • Dokyung : $3K
• Milestone 1
  • Participants : Hyung, Dongsam, Jeseon, Hanjun, Dokyung
  • Duration : 5 months
  • Budget : 5 months * $43K = $215K
• Milestone 2
  • Participants : Hyung, Dongsam, Jeseon
  • Duration : 3 months
  • Budget : 3 months * $30K = $90K
• Total budget : $215K + $90K = $305K

Rollup Comparison : Optimistic Rollup

The Advantage of Optimistic Rollup : Flexibility

• Optimistic rollup can be adopted to any kind of general computation or smart contract
• Current zk-rollup technology does not provide general computation capability
  • Therefore it is only for relatively simple computation logic
  • But the technology is towards more general computation in future
  • Reason of inflexibility of zk-rollup
    • The entire computation logic should be written in circuit program, which is very low-level language without convenient functions
    • However, developers in zk-rollup industry keep supporting various kind of high-level functions from the low-level language

Security Problems of Optimistic Rollup which can be solved by zk-rollup

• Fraud proof assumption
  • Why problem?
    • Security depends on the existence of fraud proof activities when attack comes
    • Even with generous incentives, it is very difficult to guarantee this assumption
  • Why does zk-rollup solve it?
    • zk-rollup completely guarantees computation genuinity by very fast verifier algorithm without any need of "fisherman" like activity
    • It allows zk-rollup to possess perfect layer 1 security without any security assumption
• Delayed Finality
  • Why problem?
    • Optimistic rollup requires certain duration of time(usually 1 week) for fraud provers to find any existing fraud activities on the network
    • Even after this period, we cannot say the finality is on "layer-1-level-security", because fraud proof assumption is difficult to be guaranteed
  • Why does zk-rollup solve it?
    • zk-rollup gets its layer 1 finality via mathematical proof rather than incentivized economic activities of fruad proof
    • Any state change is 100% finalized on layer 1 when verified proof is calculated by anyone, and received by layer 1
    • Finalization latency of zk-rollup depends on the calculation time of zk-proof, but such calculation work can be efficiently parallelized, the latency is matter of minutes even in 1k tps situation
    • It can be confidently guaranteed that in near future, with enough computation resource and more efficient parallel computing algorithms, the finality latency of zk-rollup will become several seconds even in 1k tps situation

Combination of Different Rollup Approach

• Usecases of Optimistic Rollup
  • more generalized computation
  • less security necessity
  • less demands on fast finality
• Usecases of zk-rollup
  • more specific and concise computation
  • perfect layer-1 security necessity : utilities with significant deposit assets to layer 2
  • high demands on fast finality : interchain utilities with transactions from different blockchains

User Benefit / Ecosystem Impact

Efficient and Secure Scalability Solution for Cosmos Ecosystem

• zk-rollup provides the most efficient and secure scalability solution for the Cosmos Hub and other Cosmos blockchains
• zk-rollup does not require significant trust on validator sets of layer 2, which allows centralized layer 2 operation
• centralized operation can minimize unnecessary incentive system for delegators and validators