Ethereum’s transition to proof of stake — The Merge — is close to: devnets are being stood up, specs are being finalized and group outreach has begun in earnest. The Merge is designed to have minimal impression on how Ethereum operates for finish customers, sensible contracts and dapps. That mentioned, there are some minor modifications value highlighting. Earlier than we dive into them, listed below are a couple of hyperlinks to offer context in regards to the total Merge structure:
The remainder of this submit will assume the reader is aware of the above. For these desirous to dig even deeper, the complete specs for The Merge can be found right here:
Block construction
After The Merge, proof of labor blocks will not exist on the community. As a substitute, the previous contents of proof of labor blocks grow to be a part of blocks created on the Beacon Chain. You may then consider the Beacon Chain as changing into the brand new proof of stake consensus layer of Ethereum, superseding the earlier proof of labor consensus layer. Beacon chain blocks will comprise ExecutionPayloads, that are the post-merge equal of blocks on the present proof of labor chain. The picture under reveals this relationship:
For finish customers and utility builders, these ExecutionPayloads are the place interactions with Ethereum occur. Transactions on this layer will nonetheless be processed by execution layer shoppers (Besu, Erigon, Geth, Nethermind, and so forth.). Luckily, because of the stability of the execution layer, The Merge introduces solely minimal breaking modifications.
Mining & Ommer Block Fields
Put up-merge, a number of fields beforehand contained in proof of labor block headers grow to be unused as they’re irrelevant to proof of stake. As a way to reduce disruption to tooling and infrastructure, these fields are set to 0, or their knowledge construction’s equal, quite than being fully faraway from the information construction. The total modifications to dam fields might be present in EIP-3675.
| Area | Fixed worth | Remark |
|---|---|---|
| ommers | [] | RLP([]) = 0xc0 |
| ommersHash | 0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347 | = Keccak256(RLP([])) |
| issue | 0 | |
| nonce | 0x0000000000000000 |
As a result of proof of stake doesn’t naturally produce ommers (a.ok.a. uncle blocks) like proof of labor, the record of those in every block (ommers) will likely be empty, and the hash of this record (ommersHash) will grow to be the RLP-encoded hash of an empty record. Equally, as a result of issue and nonce are options of proof of labor, these will likely be set to 0, whereas respecting their byte-size values.
mixHash, one other mining-related subject, will not be set to 0 however will as an alternative comprise the beacon chain’s RANDAO worth. Extra on this under.
BLOCKHASH & DIFFICULTY opcodes modifications
Put up-merge, the BLOCKHASH opcode will nonetheless be accessible to be used, however given that it’ll not be cast by way of the proof of labor hashing course of, the pseudorandomness supplied by this opcode will likely be a lot weaker.
Relatedly, the DIFFICULTY opcode (0x44) will likely be up to date and renamed to PREVRANDAO. Put up-merge, it should return the output of the randomness beacon supplied by the beacon chain. This opcode will thus be a stronger, albeit nonetheless biasable, supply of randomness for utility builders to make use of than BLOCKHASH.
The worth uncovered by PREVRANDAO will likely be saved within the ExecutionPayload the place mixHash, a price related to proof of labor computation, was saved. The payload’s mixHash subject will even be renamed prevRandao.
Right here is an illustration of how the DIFFICULTY & PREVRANDAO opcodes work pre and post-merge:
Pre-merge, we see the 0x44 opcode returns the issue subject within the block header. Put up-merge, the opcode, renamed to PREVRANDAO, factors to the header subject which beforehand contained mixHash and now shops the prevRandao worth from the beacon chain state.
This modification, formalized in EIP-4399, additionally supplies on-chain functions a method to assess whether or not The Merge has occurred. From the EIP:
Moreover, modifications proposed by this EIP permit for sensible contracts to find out whether or not the improve to the PoS has already occurred. This may be performed by analyzing the return worth of the DIFFICULTY opcode. A price better than 2**64 signifies that the transaction is being executed within the PoS block.
Block time
The Merge will impression the typical block time on Ethereum. At the moment below proof of labor, blocks are available on common each ~13 seconds with a good quantity of variance in precise block occasions. Below proof of stake, blocks are available precisely every 12 seconds besides when a slot is missed both as a result of a validator is offline or as a result of they don’t submit a block in time. In observe, this presently occurs in <1% of slots.
This means a ~1 second discount of common block occasions on the community. Good contracts which assume a specific common block time of their calculations might want to take this into consideration.
Finalized Blocks & Protected Head
Below proof of labor there’s at all times the potential for reorgs. Purposes normally await a number of blocks to be mined on prime of a brand new head earlier than treating it as unlikely to be faraway from the canonical chain, or “confirmed”. After The Merge, we as an alternative have the ideas of finalized blocks and secure head uncovered on the execution layer. These blocks can be utilized extra reliably than the “confirmed” proof of labor blocks however require a shift in understanding to make use of accurately.
A finalized block is one which has been accepted as canonical by >2/3 of validators. To create a conflicting block, an attacker must burn at the least 1/3 of the full staked ether. Whereas stake quantities could fluctuate, such an assault is at all times anticipated to value the attacker thousands and thousands of ETH.
A secure head block is one which has been justified by the Beacon Chain, that means that >2/3 of validators have attested to it. Below regular community situations, we anticipate it to be included within the canonical chain and ultimately finalized. For this block to not be a part of the canonical chain, a majority of validators would have to be colluding to assault the community, or the community must be experiencing excessive ranges of latency in block propagation. Put up-merge, execution layer APIs (e.g. JSON RPC) will expose the secure head utilizing a secure tag.
Finalized blocks will even be uncovered through JSON RPC, through a brand new finalized flag. These can then function a stronger substitute for proof of labor confirmations. The desk under summarizes this:
| Block Kind | Consensus Mechanism | JSON RPC | Circumstances for reorg |
|---|---|---|---|
| head | Proof of Work | newest | To be anticipated, should be used with care. |
| secure head | Proof of Stake | secure | Potential, requires both massive community delay or assault on community. |
| confirmed | Proof of Work | N/A | Unlikely, requires a majority of hashrate to mine a competing chain of depth > # of confirmations. |
| finalized | Proof of Stake | finalized | Extraordinarily unlikely, requires >2/3 of validators to finalize a competing chain, requiring at the least 1/3 to be slashed. |
Word: the JSON RPC specification continues to be below lively improvement. Naming modifications ought to nonetheless be anticipated.
Subsequent Steps
We hope this submit helps utility builders put together for the much-anticipated transition to proof of stake. Within the subsequent few weeks, a long-lived testnet will likely be made accessible for testing by the broader group. There’s additionally an upcoming Merge group name for infrastructure, tooling and utility builders to ask questions and listen to the newest technical updates about The Merge. See you there 👋🏻
Thanks to Mikhail Kalinin, Danny Ryan & Matt Garnett for reviewing drafts of this submit.
