oracle

Oracle

The Oracle module provides the Nibiru blockchain with an up-to-date and accurate price feed of exchange rates of trading pairs.

As price information is extrinsic to the blockchain, the Nibiru network relies on validators to periodically vote on the current exchange rates, with the protocol tallying up the results once per VotePeriod and updating the on-chain exchange rate as the weighted median of the ballot.

Since the Oracle service is powered by validators, you may find it interesting to look at the Staking module, which covers the logic for staking and validators.

Contents

• Oracle
  • Concepts
    • Voting Procedure
    • Reward Band
    • Slashing
    • Abstaining from Voting
    • Messages
  • Module Parameters
  • State
    • ExchangeRate
    • FeederDelegation
    • MissCounter
    • AggregateExchangeRatePrevote
    • AggregateExchangeRateVote
  • End Block
    • Tally Exchange Rate Votes
  • Messages
    • MsgAggregateExchangeRatePrevote
    • MsgAggregateExchangeRateVote
    • MsgDelegateFeedConsent
  • Events
    • EndBlocker
    • Events for MsgExchangeRatePrevote
    • Events for MsgExchangeRateVote
    • Events for MsgDelegateFeedConsent
    • Events for MsgAggregateExchangeRatePrevote
    • Events for MsgAggregateExchangeRateVote

Concepts

See docs.nibiru.fi/ecosystem/oracle.

Voting Procedure

During each VotePeriod, the Oracle module obtains consensus on the exchange rate of pairs specified in Whitelist by requiring all members of the validator set to submit a vote for exchange rates before the end of the interval.

Validators must first pre-commit to a exchange rate, then in the subsequent VotePeriod submit and reveal their exchange rate alongside a proof that they had pre-commited at that price. This scheme forces the voter to commit to a submission before knowing the votes of others and thereby reduces centralization and free-rider risk in the Oracle.

• Prevote and Vote

  Let P_t be the current time interval of duration defined by VotePeriod (currently set to 30 seconds) during which validators must submit two messages:

  • A MsgAggregateExchangeRatePrevote, containing the SHA256 hash of the exchange rates of pairs. A prevote must be submitted for all pairs.
  • A MsgAggregateExchangeRateVote, containing the salt used to create the hash for the aggregate prevote submitted in the previous interval P_t-1.

• Vote Tally

  At the end of P_t, the submitted votes are tallied.

  The submitted salt of each vote is used to verify consistency with the prevote submitted by the validator in P_t-1. If the validator has not submitted a prevote, or the SHA256 resulting from the salt does not match the hash from the prevote, the vote is dropped.

  For each pair, if the total voting power of submitted votes exceeds 50%, the weighted median of the votes is recorded on-chain as the effective exchange rate for the following VotePeriod P_t+1.

  Exchange rates receiving fewer than VoteThreshold total voting power have their exchange rates deleted from the store, and no exchange rate will exist for the next VotePeriod P_t+1.

• Ballot Rewards

  After the votes are tallied, the winners of the ballots are determined with tally().

  Voters that have managed to vote within a narrow band around the weighted median, are rewarded with a portion of the collected seigniorage. See k.RewardBallotWinners() for more details.

Reward Band

Let M be the weighted median, 𝜎 be the standard deviation of the votes in the ballot, and be the RewardBand parameter. The band around the median is set to be 𝜀 = max(𝜎, R/2). All valid (i.e. bonded and non-jailed) validators that submitted an exchange rate vote in the interval [M - 𝜀, M + 𝜀] should be included in the set of winners, weighted by their relative vote power.

Slashing

Be sure to read this section carefully as it concerns potential loss of funds.

A VotePeriod during which either of the following events occur is considered a "miss":

• The validator fails to submits a vote for an exchange rate against each and every pair specified in Whitelist.

• The validator fails to vote within the reward band around the weighted median for one or more pairs.

During every SlashWindow, participating validators must maintain a valid vote rate of at least MinValidPerWindow (5%), lest they get their stake slashed (currently set to 0.01%). The slashed validator is automatically temporarily "jailed" by the protocol (to protect the funds of delegators), and the operator is expected to fix the discrepancy promptly to resume validator participation.

Abstaining from Voting

A validator may abstain from voting by submitting a non-positive integer for the ExchangeRate field in MsgAggregateExchangeRateVote. Doing so will absolve them of any penalties for missing VotePeriods, but also disqualify them from receiving Oracle seigniorage rewards for faithful reporting.

Messages

The control flow for vote-tallying, exchange rate updates, ballot rewards and slashing happens at the end of every VotePeriod, and is found at the end-block ABCI function rather than inside message handlers.

Module Parameters

The oracle module contains the following parameters:

State

ExchangeRate

An sdk.Dec that stores the current exchange rate against a given pair.

You can get the active list of pairs (exchange rates with votes past VoteThreshold) with k.GetActivePairs().

• ExchangeRate: 0x03<pair_Bytes> -> amino(sdk.Dec)

FeederDelegation

An sdk.AccAddress (nibi- account) address of operator's delegated price feeder.

• FeederDelegation: 0x04<valAddress_Bytes> -> amino(sdk.AccAddress)

MissCounter

An int64 representing the number of VotePeriods that validator operator missed during the current SlashWindow.

• MissCounter: 0x05<valAddress_Bytes> -> amino(int64)

AggregateExchangeRatePrevote

AggregateExchangeRatePrevote containing validator voter's aggregated prevote for all pairs for the current VotePeriod.

• AggregateExchangeRatePrevote: 0x06<valAddress_Bytes> -> amino(AggregateExchangeRatePrevote)

// AggregateVoteHash is hash value to hide vote exchange rates
// which is formatted as hex string in SHA256("{salt}:({pair},{exchange_rate})|...|({pair},{exchange_rate}):{voter}")
type AggregateVoteHash []byte

type AggregateExchangeRatePrevote struct {
 Hash        AggregateVoteHash // Vote hex hash to protect centralize data source problem
 Voter       sdk.ValAddress    // Voter val address
 SubmitBlock int64
}

AggregateExchangeRateVote

AggregateExchangeRateVote containing validator voter's aggregate vote for all pairs for the current VotePeriod.

• AggregateExchangeRateVote: 0x07<valAddress_Bytes> -> amino(AggregateExchangeRateVote)

type ExchangeRateTuple struct {
 Pair        string  `json:"pair"`
 ExchangeRate sdk.Dec `json:"exchange_rate"`
}

type ExchangeRateTuples []ExchangeRateTuple

type AggregateExchangeRateVote struct {
 ExchangeRateTuples ExchangeRateTuples // ExchangeRates of pairs
 Voter              sdk.ValAddress     // voter val address of validator
}

End Block

Tally Exchange Rate Votes

At the end of every block, the Oracle module checks whether it's the last block of the VotePeriod. If it is, it runs the Voting Procedure:

1. All current active exchange rates are purged from the store

2. Received votes are organized into ballots by pair. Abstained votes, as well as votes by inactive or jailed validators are ignored

3. Pairs not meeting the following requirements will be dropped:

   • Must appear in the permitted pairs in Whitelist
   • Ballot for pair must have at least VoteThreshold total vote power

4. For each remaining pair with a passing ballot:

   • Tally up votes and find the weighted median exchange rate and winners with tally()
   • Iterate through winners of the ballot and add their weight to their running total
   • Set the exchange rate on the blockchain for that pair with k.SetExchangeRate()
   • Emit an exchange_rate_update event

5. Count up the validators who missed the Oracle vote and increase the appropriate miss counters

6. If at the end of a SlashWindow, penalize validators who have missed more than the penalty threshold (submitted fewer valid votes than MinValidPerWindow)

7. Distribute rewards to ballot winners with k.RewardBallotWinners()

8. Clear all prevotes (except ones for the next VotePeriod) and votes from the store

Messages

MsgAggregateExchangeRatePrevote

Hash is a hex string generated by the leading 20 bytes of the SHA256 hash (hex string) of a string of the format {salt}:({pair},{exchange_rate})|...|({pair},{exchange_rate}):{voter}, the metadata of the actual MsgAggregateExchangeRateVote to follow in the next VotePeriod. You can use the GetAggregateVoteHash() function to help encode this hash. Note that since in the subsequent MsgAggregateExchangeRateVote, the salt will have to be revealed, the salt used must be regenerated for each prevote submission.

// MsgAggregateExchangeRatePrevote - struct for aggregate prevoting on the ExchangeRateVote.
// The purpose of aggregate prevote is to hide vote exchange rates with hash
// which is formatted as hex string in SHA256("{salt}:({pair},{exchange_rate})|...|({pair},{exchange_rate}):{voter}")
type MsgAggregateExchangeRatePrevote struct {
 Hash      AggregateVoteHash 
 Feeder    sdk.AccAddress    
 Validator sdk.ValAddress    
}

Feeder (nibi- address) is used if the validator wishes to delegate oracle vote signing to a separate key (who "feeds" the price in lieu of the operator) to de-risk exposing their validator signing key.

Validator is the validator address (nibivaloper- address) of the original validator.

MsgAggregateExchangeRateVote

The MsgAggregateExchangeRateVote contains the actual exchange rates vote. The Salt parameter must match the salt used to create the prevote, otherwise the voter cannot be rewarded.

// MsgAggregateExchangeRateVote - struct for voting on the exchange rates of pairs.
type MsgAggregateExchangeRateVote struct {
 Salt          string
 ExchangeRates string
 Feeder        sdk.AccAddress 
 Validator     sdk.ValAddress 
}

MsgDelegateFeedConsent

Validators may also elect to delegate voting rights to another key to prevent the block signing key from being kept online. To do so, they must submit a MsgDelegateFeedConsent, delegating their oracle voting rights to a Delegate that sign MsgAggregateExchangeRatePrevote and MsgAggregateExchangeRateVote on behalf of the validator.

Delegate validators will likely require you to deposit some funds (in NIBI) which they can use to pay fees, sent in a separate MsgSend. This agreement is made off-chain and not enforced by the Nibiru protocol.

The Operator field contains the operator address of the validator (prefixed nibivaloper-). The Delegate field is the account address (prefixed nibi-) of the delegate account that will be submitting exchange rate related votes and prevotes on behalf of the Operator.

// MsgDelegateFeedConsent - struct for delegating oracle voting rights to another address.
type MsgDelegateFeedConsent struct {
 Operator sdk.ValAddress 
 Delegate sdk.AccAddress 
}

Events

The oracle module emits the following events:

EndBlocker

Events for MsgExchangeRatePrevote

Events for MsgExchangeRateVote

Events for MsgDelegateFeedConsent

Events for MsgAggregateExchangeRatePrevote

Events for MsgAggregateExchangeRateVote