5.4 KiB
Tributary
A tributary is a side-chain, created for a specific multisig instance, used as a verifiable broadcast layer.
Transactions
Key Gen Commitments
DkgCommitments is created when a processor sends the coordinator
key_gen::ProcessorMessage::Commitments. When all validators participating in
a multisig publish DkgCommitments, the coordinator sends the processor
key_gen::CoordinatorMessage::Commitments, excluding the processor's own
commitments.
Key Gen Shares
DkgShares is created when a processor sends the coordinator
key_gen::ProcessorMessage::Shares. The coordinator additionally includes its
own pair of MuSig nonces, used in a signing protocol to inform Substrate of the
key's successful creation.
When all validators participating in a multisig publish DkgShares, the
coordinator sends the processor key_gen::CoordinatorMessage::Shares, excluding
the processor's own shares and the MuSig nonces.
Key Gen Confirmation
DkgConfirmed is created when a processor sends the coordinator
key_gen::ProcessorMessage::GeneratedKeyPair. The coordinator takes the MuSig
nonces they prior associated with this DKG attempt and publishes their signature
share.
When all validators participating in the multisig publish DkgConfirmed, an
extrinsic calling validator_sets::pallet::set_keys is made to confirm the
keys.
Setting the keys on the Serai blockchain as such lets it receive Batchs,
provides a BFT consensus guarantee, and enables accessibility by users. While
the tributary itself could offer both the BFT consensus guarantee, and
verifiable accessibility to users, they'd both require users access the
tributary. Since Substrate must already know the resulting key, there's no value
to usage of the tributary as-such, as all desired properties are already offered
by Substrate.
Note that the keys are confirmed when Substrate emits a KeyGen event,
regardless of if the Tributary has the expected DkgConfirmed transactions.
External Block
When TODO, a ExternalBlock transaction is provided. This is used to have
the group acknowledge and synchronize around the block, without the overhead of
voting in its acknowledgment.
When a ExternalBlock transaction is included, participants are allowed to
publish transactions to produce a threshold signature for the block's Batch.
Substrate Block
SubstrateBlock is provided when the processor sends the coordinator
substrate::ProcessorMessage::SubstrateBlockAck.
When a SubstrateBlock transaction is included, participants are allowed to
publish transactions for the signing protocols it causes.
Batch Preprocess
BatchPreprocess is created when a processor sends the coordinator
coordinator::ProcessorMessage::BatchPreprocess and an ExternalBlock
transaction allowing the batch to be signed has already been included on chain.
When t validators have published BatchPreprocess transactions, if the
coordinator represents one of the first t validators to do so, a
coordinator::ProcessorMessage::BatchPreprocesses is sent to the processor,
excluding the processor's own preprocess.
Batch Share
BatchShare is created when a processor sends the coordinator
coordinator::ProcessorMessage::BatchShare. The relevant ExternalBlock
transaction having already been included on chain follows from
coordinator::ProcessorMessage::BatchShare being a response to a message which
also has that precondition.
When the t validators who first published BatchPreprocess transactions have
published BatchShare transactions, if the coordinator represents one of the
first t validators to do so, a coordinator::ProcessorMessage::BatchShares
with the relevant shares (excluding the processor's own) is sent to the
processor.
Sign Preprocess
SignPreprocess is created when a processor sends the coordinator
sign::ProcessorMessage::Preprocess and a SubstrateBlock transaction
allowing the transaction to be signed has already been included on chain.
When t validators have published SignPreprocess transactions, if the
coordinator represents one of the first t validators to do so, a
sign::ProcessorMessage::Preprocesses is sent to the processor,
excluding the processor's own preprocess.
Sign Share
SignShare is created when a processor sends the coordinator
sign::ProcessorMessage::Share. The relevant SubstrateBlock transaction
having already been included on chain follows from
sign::ProcessorMessage::Share being a response to a message which
also has that precondition.
When the t validators who first published SignPreprocess transactions have
published SignShare transactions, if the coordinator represents one of the
first t validators to do so, a sign::ProcessorMessage::Shares with the
relevant shares (excluding the processor's own) is sent to the processor.
Sign Completed
SignCompleted is created when a processor sends the coordinator
sign::ProcessorMessage::Completed. As soon as 34% of validators send
Completed, the signing protocol is no longer further attempted.
Re-attempts
Key generation protocols may fail if a validator is malicious. Signing
protocols, whether batch or transaction, may fail if a validator goes offline or
takes too long to respond. Accordingly, the tributary will schedule re-attempts.
These are communicated with key_gen::CoordinatorMessage::GenerateKey,
coordinator::CoordinatorMessage::BatchReattempt, and
sign::CoordinatorMessage::Reattempt.
TODO: Document the re-attempt scheduling logic.