Fantom: Consensus practically explained

In this article, we will compare time ordering, proof of work (PoW), proof of stake (PoS), and lachesis (fantom consensus) in simple to understand practical examples.

Time Ordering

Alice has 1FTM, Charlie has 1FTM, Bob has 1FTM

Alice sends Bob 1FTM
Bob sends Alice 1FTM
Charlie sends Bob 1FTM

Time ordering results

Result: Alice has 1 FTM, Bob has 2FTM, Charlie has 0FTM

Sadly, blockchains have no inherent or agreed upon concept of time, so we can’t use this.

Proof of Work (PoW)

Alice, Bob, and Charlie are each given the same crossword puzzle. The one that finishes it first, can decide the ordering.

Alice wins, they order it as follows;

Charlie sends Bob 1FTM
Bob sends Alice 1FTM

Result: Alice has 2FTM, Bob has 1FTM, Charlie has 0FTM

Bob wins, they order it as follows;

Alice sends Bob 1FTM
Charlie sends Bob 1FTM

Result: Alice has 0FTM, Bob has 3FTM, Charlie has 0FTM

As we can see from the above, the person that wins, has a lot of power.

Proof of Stake (PoS)

Alice suggests the first ordering, in order to suggest they “bet” (stake) all their FTM that they won’t cheat, they suggest;

Charlie sends Bob 1FTM
Bob sends Alice 1FTM

Alice shows their suggestion to Bob, and Charlie. Bob, and Charlie prove that Alice left out that they sent Bob 1FTM, Alice loses their “bet” (stake). Assuming Alice didn’t cheat, and instead suggested;

Alice send Bob 1FTM
Bob sends Alice 1FTM
Charlie sends Bob 1FTM

Alice shows their suggestion to Bob, and Charlie. Bob checks what Alice suggested and they approve, so they also “bet” (stake) all their FTM that it is correct. Charlie does the same.

Since 2+ out of 3 participants agreed it is correct, it is considered valid.

With each proposal, the proposer needs to contact all known parties and get their feedback.

Lachesis (Fantom consensus)

Each time one of the parties interact with each other, they share all the other knowledge they have with each other;

Alice sends Bob 1FTM, Alice & Bob know that Alice sent Bob 1FTM
Bob sends Alice 1FTM, Alice & Bob know that Alice sent Bob 1FTM, and that Bob sent Alice 1FTM
Charlie sends Bob 1FTM, Bob tells Charlie that Alice sent Bob 1FTM, and that Bob sent Alice 1FTM

Since Bob is aware of the transactions between Alice & Bob & Charlie, and Charlie is aware of the transactions between Alice & Bob & Charlie, 2 out of 3 participants have agreed, it is considered valid.

Consensus was achieved through normal interaction.

Conclusion

As can be seen with PoW, results can vary and it is highly dependent on how long each participant takes to finish the puzzle.

As can be seen with PoS, results are more consistent, however each time multiple rounds of communication must occur between all parties to agree.

As can be seen with Lachesis, results are time ordered and requires no additional rounds of communication.

The above is grossly oversimplified, and in future articles I will dig deeper into what differentiates Fantom consensus even further, but the above should be able to showcase that Fantom consensus is horizontally scalable (as more parties are introduced the complexity of communication remains the same — unlike PoS), and it has inherent time ordering. The above is why Fantom is the only blockchain with consistent sub second finality.