Graypaper: The JAM Specification

The description and formal specification of the Jam protocol, a potential successor to the Polkadot Relay chain.

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https://graypaper.com/

Remaining near-term

Finesse

• Make all subscript names capitalized
• Ensure all definitions are referenced
• Link and integrate to Bandersnatch RingVRF references (Davide/Syed) IN-PROGRESS
• Remove any "TODOs" in text
• Macrofy everything
• Limit number of extrinsics in a WP.

Final PVM

• 64-bit PVM
• Gas pricing
  • Merkle reads in terms of nodes traversed.
  • Non-linear gas for export/import host calls
• No pages mappable in first 64 KB

Final DA

• Formalize as much as possible.
• Migrate formalization & explanation:
  • guaranteeing-specific stuff into relevant section
  • assurance-specific stuff into relevant section
  • auditing-specific stuff into relevant section
• Include an epochal on-chain lookup from Work Package hash to segments root.
  • Allow import spec to be given as either WP hash (in case of being recent) or segments root.
  • How can this work given that WP hash to segments-root needs to happen in-core?
  • Include a bond to any SR->WPh lookups in the WR.
  • Check these bonds only just prior to accumulation; if they fail, drop the report and reduce the guarantors' points.
  • Update on-chain SR->WPh immediately at the time of being reported (don't want for accumulation).
• Define Erasure Coding proof means
  • Define binary Merkle proof-generation function which compiles neighbours down to leaf.
  • Define binary Merkle proof-verification function exists sequence of values which contains our value and Merklised to some root.

Guaranteeing & Auditing

• Guarantees by validator indices
• Specify announcement signatures
• Specify how to build perspective on other validators with announcements

Discussion and Conclusions/Further Work

• Security assumptions: redirect to ELVES paper
• Creating a parachains service: further work (RFC for upgrade perhaps)
  • Key differences
    • limited size of Work Output vs unlimited candidate receipt
    • Laissez-faire on Work Items vs requirement for valid transition
    • Hermit relay (staking &c is on system chains)
  • Supporting liveness
  • Supporting *MP
  • No need for UMP/DMP
• Compare with danksharding v1
• Deeper talk Cost & latency comparison with RISC0-VM and latest ZK stuff.
• Include full calculations for bandwidth requirements.

Stuff before 1.0

Final networking protocol

• Consider a simple network protocol needed for M1/M2 and a production protocol for M3+
• Block distribution via EC and proactive-chunk-redistribution
• Guarantor-guarantor handover
• Star-shaped Point-to-point extrinsic distribution
• Mixnet for ticket submission

Bring together sub-protocols

• Better integration to Grandpa paper
• Better description of Beefy
• Better integration to Bandersnatch RingVRF.

Ideas to consider

Work Packages

At present all WorkItems can succeed or fail independently. Instead we should be able to specify co-dependency criteria, so that if one fails, both fail. This should be respected through to accumulation, whereby an accumulator can commit to accumulating the WorkResult iff there is a signal from the other accumulator that the result has been accumulated there.

Statistics/Bookkeeping

• Consider integrating the subjective extrinsic and state:
  • If so, have three items to allow for a whole epoch of opinion submission
  • In which case allow for guaranteeing val keys from last epoch to gain points

General

• Think about time and relationship between lookup-anchor block and import/export period.
  • Lookup anchor: maybe it should be 48 hours since lookup anchor can already be up to 24 hours after reporting and we want something available up to 24 hours after that?
• Refine arguments:
  • Currently passing in the WP hash, some WP fields and all manifest preimages: Consider passing in the whole work-package and a work-item index.
• Consider removal of the arrow-above notation in favour of subscript and ellipsis (this only works for the right-arrow).
• Optional on_report entry point
• Remove assignments from state - no need for it to be there as it's derivable from $\eta_2$ alone.
• Make memo bounded, rather than fixed.

Done

• Statistics/Bookkeeping
  • Integrate into intro and definitions.
• All "where" and "let" lines are unnumbered/integrated
• DA2
  • Update chunks/segments to new size of 12 bytes / 4KB in the availability sections, especially the work-packages and work-reports section and appendix H.
  • export is in multiples of 4096 bytes.
  • Manifest specifies WI (maximum) export count.
  • import is provided as concatenated segments of 4096 bytes, as per manifest.
  • Constant-depth merkle root
  • (Partial) Merkle proof generation function
  • New erasure root (4 items per validator; 2 hashes + 2 roots).
  • Specification of import hash (to include concatenated import data and proof).
    • Proof spec.
    • Specification of segment root.
  • Additional two segment-roots in WR.
    • Specification of segment tree.
  • Specification of segment proofs.
  • Specification of final segments for DA and ER.
  • Re-erasure-code imports.
  • Fetching imports and verification.
• Independent definition of PVM.
• Need to translate the basic work result into an "L"; do it in the appendix to ease layout
  • service - easy
  • service code hash - easy
  • payload hash - easy
  • gas prioritization - just from WP?
• Edit Previous Work.
• Edit Discussion.
• Document guide at beginning.
• Move constants to appendix and define at first use.
• Context strings for all signatures.
  • List of all context strings in definitions.
• Remove header items from ST dependency graph where possible.
• Update serialization
  • For $\beta$ component $b$ - implement MMR encode.
  • Additional field: $\rho_g$
• Link and integrate to RISCV references (Jan) HAVE SPEC
• Link and integrate to Beefy signing spec (Syed)
• Link and integrate to Erasure-Coding references (work with Al)
• Grandpa/best-block: Disregard blocks which we believe are equivocated unless finalized.
• Other PVM work
  • Define sbrk properly:
  • Update host functions to agreed API.
  • Figure out what to do with the jump table.
• Define inner PVM host-calls
  • Spec below
  • Figure out what the $c_i$/$c_b$ are
  • Avoid entry point
  • Ensure code and jump-table is amalgamated down to VM-spec
  • Move host calls to use register index
• Update serialization for Judgement extrinsic and judgements state.
• Define Beefy process
  • Accumulate: should return Beefy service hash
  • Define Keccak hash $\mathbb{H}_K$
  • Remove Beefy root from header
  • Put the Beefy root into recent blocks after computation
  • Recent blocks should store MMR of roots of tree of accumulated service hashes
  • Define an MMR
  • Add \textsc{bls} public key to keyset (48 octet).
  • Specify requirement of validators to sign.
• Define audit process.
  • Erasure coding root must be correct
  • This means we cannot assume that the WP hash can be inverted.
  • Instead, we assume that we can collect 1/3 chunks and combine to produce some data
  • Then we check:
    • if that hashes to the WP hash.
    • if the erasure-coded chunks merklise into a tree of the given root.
  • If so we continue.
  • NOTE: The above should be done in guarantor stage also.
• Auditing: Always finish once announced.
• Judgements: Should cancel work-report from Rho prior to accumulation.
• Signed judgements should not include guarantor keys;
  • Judgement extrinsic should use from rho.
• Check "Which History" section and ensure it mentions possibility for reversion via judgement.
  • No reversion beyond finalized
  • Of unfinalized extension, not block containing work-reports which appear in the banned-set of any other (valid) block.
• Prior work and refine/remove the zk argumentation (work with Al)
• Disputes state transitioning and extrinsic (work with Al)
• Finish Merklization description
• Bibliography
• Updated PVM
• Remove extrinsic segment root. Rename "* segment-root" to just "segment-root".
• Combine chunk-root for WP, concatenated extrinsics and concatenated imports.
• Imports are host-call
• Make work-report field r bold.
• Segmented DA v2
  • Underlying EC doesn't change, need to make clear segments are just a double-EC
• Make work-report field r bold.
• Need to translate the basic work result into an "L"; do it in the appendix to ease layout
  • service - easy
  • service code hash - easy
  • payload hash - easy
  • gas prioritization - just from WP?
  • Consider introducing a host-call for reading manifest data rather than always passing it in.

ELVES

• Don't immediately alter kappa mid-epoch as it affects off-chain judgements.
• Instead, apply the blacklist to guarantor sig verification directly.
• Include the core in the WR.
• Deposit the WR's signatures in with the judgement.
• Require at >= 1 negative judgements to be included with a positive verdict, and place signer in offender keys.
• Serialization of judgement stuff
• Should always be possible to submit more guarantee signatures of a known-bad report to place them in the offender set.
  • Only from lambda and kappa?
• Use posterior kappa for everything except judgements.

% A set of independent, sequential, asynchronously interacting 32-octet state machines each of whose transitions lasts around 2 seconds of webassembly computation if a predetermined and fixed program and whose transition arguments are 5 MB. While well-suited to the verification of substrate blockchains, it is otherwise quite limiting.