This is the first part of many (we hope) articles about Ethereum 2.0 as we get closer to its release.

NOTE: Things have changed in the 0.9 spec of the beacon chain and I have amended some of the descriptions accordingly.

Serenity or Ethereum 2.0 is the long awaited and even longer in the works move of the Ethereum network from Proof-of-Work to Proof-of-Stake, together with some huge upgrades on the scalability side. An important milestone on this has been the spec freeze of the first phase of development and we can now start seeing the results of the incredible amount of hard work that was put into research and development.

When I started looking into Serenity (or Ethereum 2.0!), the first thing that made me feel at a loss was the abundance of completely new terms. What the heck is a crosslink? Is a slot a block?[Spoiler, no, it isn’t]. Is an attestor the same thing as a validator?

The following list tries to describe the most used terms in the Ethereum two point ohh universe for the mildly technical Ethereum user. Bear in mind this is not an exhaustive list, but focuses on the most prominent details you might have questions about.

If you notice any inconsistencies or want to get in touch with us for any reason, please reach out over Twitter or our newly created Discord channel.

Beacon Chain

one chain to rule them all

proof-of-stake chain

includes beacon blocks

the consensus layer for everything

manages validators

applies rewards and penalties

serves as an anchor point for the shards through cross-links

Shards

1̵0̵2̵4̵ ̵o̵f̵ ̵t̵h̵e̵m̵ 64 of them

semi independent chains

include shard blocks

periodically the state of the shard blocks is recorded on the beacon chain through crosslinks

once a block on the beacon chain is finalised, the shard blocks referenced in the included crosslinks are considered finalised

each shard has a committee of validators attesting blocks

Crosslinks

a summary of the shard’s state

only reference of the shards in the beacon chain

each shard will be linked every block

Slot

period of time in which a block proposer propose a block for attestation

slots might be empty

slots are filled with attested blocks

Epoch

a number of slots (c̵u̵r̵r̵e̵n̵t̵l̵y̵ ̵6̵4̵ currently 32) after which validators are reshuffled in committees

Validators

users that have deposited 32eth in the validator deposit contract and run a validator node

they can be inactive (don’t run as an actual validator yet), active (validating), pending (opted into becoming a validator but stuck in the entry queue) and exiting (no longer want to validate and stuck in the exit queue)

Block Proposers

random validators chosen by the beacon chain to propose blocks for validation/attestation

there will be one block proposer per slot for the beacon chain and one proposer per slot for each of the shards

Attestations

votes in regards to the validity of a shard block or beacon

Committees

random groups of validators chosen by the beacon chain to attest the validity of blocks (beacon & shard)

target of minimum 128 validators per committee

ETH2 or BETH

base currency of the beacon chain

will be obtained initially from rewards and by locking ETH1 in the validator deposit contract

Validator Deposit Contract

smart contract on the POW chain (in our case, the Ethereum Mainnet)

once ETH1 funds are locked in this smart contract, and event log is emitted that should be read by the beacon chain and the same amount of ETH2 should be allocated to the account, now considered a validator

this mechanism might change in the future

until phase 2 ends the transfer of ETH1 to ETH2 is a one way street, can’t get ETH1 back, but there is an escape hatch to sell your stake once transfers between validators become possible

Ethereum 2.0 phases

Phase 0 — The beacon chain

managing validators and stakes

organizing and electing committees and proposers

applying consensus rules

rewarding and penalizing/slashing

Phase 1 — Shards

constructing the shard chains and blocks

anchoring (cross-linking) shard blocks to beacon chain

ability to do bETH transfers between validators (this might come sooner as it’s not technically linked to work on sharding)

Phase 2 — Execution Environments

Ewasm based virtual machine for execution of the… execution environments

every shard has access to all execution environments

ability to make transactions within execution environments

ability to run and interact with smart contracts

cross-shard communication

Authoritative info is hard to come by on this subject so many thanks to Ben Edgington for setting me straight on some of the things above. Would also like to thank Danny Ryan, Everett Muzzy and Will Villanueva for additional corrections.