Module hbbft::subset

Subset algorithm.

The Subset protocol assumes a network of N nodes that send signed messages to each other, with at most f of them malicious, where 3 f < N. Handling the networking and signing is the responsibility of the user: only when a message has been verified to be "from node i" (e.g. using cryptographic signatures), it can be handed to the Subset instance.

Each node proposes an element for inclusion. Under the above conditions, the protocol guarantees that all correct nodes output the same set, consisting of at least N - f of the proposed elements.

How it works

• Subset instantiates one Broadcast algorithm for each of the participating nodes. At least N - f of these - the ones whose proposer is not faulty - will eventually output the element proposed by that node.
• It also instantiates Binary Agreement for each participating node, to decide whether that node's proposed element should be included in the set. Whenever an element is received via broadcast, we input "yes" (true) into the corresponding BinaryAgreement instance.
• When N - f BinaryAgreement instances have decided "yes", we input "no" (false) into the remaining ones, where we haven't provided input yet.
• Once all BinaryAgreement instances have decided, Subset returns the set of all proposed values for which the decision was "yes".

Structs

Message	Message from Subset to remote nodes.
Subset	Subset algorithm instance

Enums

Error	A subset error.
FaultKind	Faults that can be detected in Subset.
MessageContent	A message about a particular proposer's contribution.
SubsetOutput	An output with an accepted contribution or the end of the set.

Type Definitions

Result	A subset result.
Step	A Subset step, possibly containing several outputs.