starting a bft node

BFT stands for the Byzantine Fault Tolerant (read the paper).

Jormungandr allows you to start a BFT blockchain fairly easily. The main downside is that it is centralized, only a handful of nodes will ever have the right to create blocks.

How does it work

It is fairly simple. A given number of Nodes (N) will generate a key pairs of type Ed25519 (see JCLI’s Keys).

They all share the public key and add them in the genesis.yaml file. It is the source of truth, the file that will generate the first block of the blockchain: the Block 0.

Then, only by one after the other, each Node will be allowed to create a block. Utilising a Round Robin algorithm.

Example of genesis file

  block0_date: 1550822014
  discrimination: test
  block0_consensus: bft
  slots_per_epoch: 5
  slot_duration: 15
  epoch_stability_depth: 10
    - ed25519e_pk1k3wjgdcdcn23k6dwr0cyh88ad7a4ayenyxaherfazwy363pyy8wqppn7j3
    - ed25519e_pk13talprd9grgaqzs42mkm0x2xek5wf9mdf0eefdy8a6dk5grka2gstrp3en
  consensus_genesis_praos_active_slot_coeff: 0.22
    constant: 2
    coefficient: 1
    certificate: 4
  kes_update_speed: 43200
  - fund:
      - address: ta1svy0mwwm7mdwcuj308aapjw6ra4c3e6cygd0f333nvtjzxg8ahdvxlswdf0
        value: 10000
  - cert: cert1qgqqqqqqqqqqqqqqqqqqq0p5avfqqmgurpe7s9k7933q0wj420jl5xqvx8lywcu5jcr7fwqa9qmdn93q4nm7c4fsay3mzeqgq3c0slnut9kns08yn2qn80famup7nvgtfuyszqzqrd4lxlt5ylplfu76p8f6ks0ggprzatp2c8rn6ev3hn9dgr38tzful4h0udlwa0536vyrrug7af9ujmrr869afs0yw9gj5x7z24l8sps3zzcmv
  - legacy_fund:
      - address: 48mDfYyQn21iyEPzCfkATEHTwZBcZJqXhRJezmswfvc6Ne89u1axXsiazmgd7SwT8VbafbVnCvyXhBSMhSkPiCezMkqHC4dmxRahRC86SknFu6JF6hwSg8
        value: 123

In order to start your blockchain in BFT mode you need to be sure that:

  • consensus_leader_ids is non empty;

more information regarding the genesis file here.

Creating the block 0

jcli genesis encode --input genesis.yaml --output block-0.bin

This command will create (or replace) the Block 0 of the blockchain from the given genesis configuration file (genesis.yaml).

Starting the node

Now that the blockchain is initialized, you need to start your node.

Write your private key in a file on your HD:

$ cat node_secret.yaml
  signing_key: ed25519_sk1hpvne...

Configure your Node (config.yml) and run the following command:

$ jormungandr --genesis-block block-0.bin \
    --config example.config \
    --secret node_secret.yaml

It’s possible to use the flag --secret multiple times to run a node with multiple leaders.

Step by step to start the BFT node

  1. Generate initial config jcli genesis init > genesis.yaml

  2. Generate secret key, e.g. jcli key generate --type=Ed25519 > key.prv

  3. Put secret key in a file, e.g. node_secret.yaml as follows:

    signing_key: ed25519_sk1kppercsk06k03yk4qgea....
  4. Generate public key out of previously generated key cat key.prv | jcli key to-public

  5. Put generated public key as in genesis.yaml under consensus_leader_ids:

  6. Generate block = jcli genesis encode --input genesis.yaml --output block-0.bin

  7. Create config file and store it on your HD as node.config e.g. ->

      level: trace
      format: json
      listen: ""
      public_address: /ip4/
        messages: low
        blocks: normal
  8. Start Jörmungandr node :

    jormungandr --genesis-block block-0.bin --config node.config --secret node_secret.yaml


Additionally, there is a script here that can be used to bootstrap a test node with bft consensus protocol.