This repository shares my implementation of a toy state machine replication built on top of the dolev-strong protocol for educational purposes.

• src/: Contains the main source code for the protocol and state machine.
• main.py: Run this script to start a protocol simulation.
• tests/: Includes test cases for validating protocol correctness.
• assets/ & recording/: Visual resources for documentation and examples.

The program will output the register value and history(append-only log) of each honest node for each dolev-strong protocol cycle(or epoch). We should see that all honest nodes have the same register value and history at the end of each cycle.

Node 0's register value is 0
Node 0's history is []
Node 3's register value is 0
Node 3's history is []

• non-sender: does not participate in the protocol
• sender:
  • sometime, send value $v1$ to half of the non-senders and send value $v2$ to another half of the non-senders
  • sometime, it follows the protocol correctly (it acts as an honest node)

Occasionally, the register values of honest nodes may differ, but their histories remain identical because the executor has not yet applied the latest record.

The dolev-Strong protocol is an authenticated protocol for solving broadcast, against any adversary controlling t<n out of n parties, in t+1 rounds.

1. Permissioned: a prior known set of nodes ${1, 2, 3, ..., n}$.
2. Public Key Infrastructure: each node has a pair of $pk_i$, $sk_i$ where $pk_i$ is known to all nodes upfront.
3. Synchronous Network:
   1. all nodes share a global clock, time steps from ${0, 1, 2, ...}$.
   2. the message sent from time $t$ will be arrived at time $t+1$ (in some arbitrary order).
4. Node Failure: there are $f$ number of nodes that can be byzantine.

1. https://decentralizedthoughts.github.io/2019-12-22-dolev-strong/
2. https://www.cs.umd.edu/~jkatz/gradcrypto2/NOTES/lecture26.pdf
3. https://elaineshi.com/docs/blockchain-book.pdf