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terminology.md

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Categories of Terms

Label Category
CP Core Property
F Faults
N Network

Terminology

In order alphabetically by Label then by Term, or just Term if there is no Label.

Label Term Definition
CP Liveness Every correct propsed value will eventually be accepted by correct nodes. aka something good happens.
CP Safety If a value is committed by a correct node, then that value will eventually be commited by all correct nodes. Two correct nodes will never commit to different values. aka nothing bad happens.
CP Chain Agreement with Immediate Finality At any point in time, for any two honest nodes n1 and n2, either the blockchain of n1 is a prefix of the blockchain of n2 or the blockhain of n2 is a prefix for the blockchain of n1. If two blockchains are identical, then each of them is a prefix of the other.
Cryptographic Hash Function A collision resistant hash function that cannot feasibly be reversed by a computationally bound adversary.
Global Stabalization Time (GST) "A time unknown to the processors, such that the message system respects the upper bound from time GST onward." (DLS Consensus in the Presence of Partial Synchrony)
Linearizability
F Fault Tolerance A system / protocol can handle faults in system, where nodes die and never deliver messages.
F Byzantine Fault Tolerance Can handle faulty nodes including malicious (Byzantine nodes) that may collude, send arbitrary data, delay correct nodes, or not send data at all.
F Consensus Protocol with Optimal Byzantine Fault Tolerance in Partially Synchronous and Asynchronous Networks Consensus protocol that can withstand up to floor((n - 1)/ 3) Byzantine nodes when operating in either a partially synchronous or asynchronous network where n is the total number of the nodes participating in the consensus protocol. As a consequence of this, the number n of nodes participating in the consensus must be n >= 3f + 1 where f corresponds to the maximum number of Byzantine nodes. This is a proven upper bound on the number of Byzantine nodes.
N Asynchronous Network No known bounds on message delivery.
N Synchronous Network Known bounds on message delivery, and processing time.
N Partially Synchronous Network There exits a finite, but unknown, upper bound on the message latency [1].
N Eventually Synchronous Network From [1]:
  • There exists a finite, but unknown, point in time called GST (Global Stabilization Time).
  • There does not exist any upper bound on the latency of messages sent before GST.
  • Messages sent before GST may never reach destination.
  • There exists a finite upper bound Δ on the latency of messages sent at a time greater than, or equal to, GST.
  • The value of Δ is unknown.
N Weak Synchrony (same as partially synchronous) "The network can be asynchronous (i.e., entirely controlled by the adversary) for a long but bounded period." (Algorand)
Quorum Certificate (QC) A (cryptographically signed) set of votes from a quorum of nodes in the system.
Responsiveness "A non-faulty proposer can drive the protocol to consensus in time depending only on the actual message delays, independent on any known upper bounds on message delays." (YMRGA Hotstuff: BFT Consensus in the Lens of Blokchain)
Optimal Responsivess Responsiveness ony after GST is reached.
Robustness Preserves safety and liveness.
View Change The phase that occurs after a primary fails. Protocol for changing the proposer.

[1] C. Dwork, N. Lynch, L. Stockmeyer, Consensus in the presence of partial synchrony, J. ACM 35 (2) (1988) 288�323. doi:10.1145/42282.42283. URL http://doi.acm.org/10.1145/42282.42283