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Replace ExternalBlock with Batch

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The initial TODO was simply to use one ExternalBlock per all batches in the
block. This would require publishing ExternalBlock after the last batch,
requiring knowing the last batch. While we could add such a pipeline, it'd
require:

1) Initial preprocesses using a distinct message from BatchPreprocess
2) An additional message sent after all BatchPreprocess are sent

Unfortunately, both would require tweaks to the SubstrateSigner which aren't
worth the complexity compared to the solution here, at least, not at this time.

While this will cause, if a Tributary is signing a block whose total batch data
exceeds 25 kB, to use multiple transactions which could be optimized out by
'better' local data pipelining, that's an extreme edge case. Given the temporal
nature of each Tributary, it's also an acceptable edge.

This does no longer achieve synchrony over external blocks accordingly. While
signed batches have synchrony, as they embed their block hash, batches being
signed don't have cryptographic synchrony on their contents. This means
validators who are eclipsed may produce invalid shares, as they sign a
different batch. This will be introduced in a follow-up commit.
This commit is contained in:
Luke Parker
2023-08-31 22:48:02 -04:00
parent 2dc35193c9
commit 9a5f8fc5dd
7 changed files with 58 additions and 120 deletions
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18
docs/coordinator/Tributary.md
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@@ -46,14 +46,14 @@ 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
### Batch
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 *TODO*, a `Batch` transaction is provided. This is used to have the group
acknowledge and synchronize around a batch, 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`.
When a `Batch` transaction is included, participants are allowed to publish
transactions to produce a threshold signature for the batch synchronized over.
### Substrate Block
@@ -66,8 +66,8 @@ 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.
`coordinator::ProcessorMessage::BatchPreprocess` and an `Batch` 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
@@ -77,7 +77,7 @@ excluding the processor's own preprocess.
### Batch Share
`BatchShare` is created when a processor sends the coordinator
`coordinator::ProcessorMessage::BatchShare`. The relevant `ExternalBlock`
`coordinator::ProcessorMessage::BatchShare`. The relevant `Batch`
transaction having already been included on chain follows from
`coordinator::ProcessorMessage::BatchShare` being a response to a message which
also has that precondition.