HomeEthereumHow The Merge Impacts Ethereum’s Software Layer

How The Merge Impacts Ethereum’s Software Layer


Be aware: this put up was up to date in March 2022 to mirror the most recent adjustments to specs.
These embrace the renaming of consensus layer specs to “Bellatrix”, the renaming of the RANDOM opcode to PREVRANDO and JSON RPC specification adjustments.

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 influence on how Ethereum operates for finish customers, good contracts and dapps. That stated, there are some minor adjustments price highlighting. Earlier than we dive into them, listed below are just a few hyperlinks to offer context in regards to the total Merge structure:

The remainder of this put up will assume the reader is accustomed to the above. For these eager to dig even deeper, the total 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 turn out to be a part of blocks created on the Beacon Chain. You possibly can then consider the Beacon Chain as turning 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 exhibits 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 on.). Happily, because of the stability of the execution layer, The Merge introduces solely minimal breaking adjustments.

Mining & Ommer Block Fields

Submit-merge, a number of fields beforehand contained in proof of labor block headers turn out to be unused as they’re irrelevant to proof of stake. To be able to decrease disruption to tooling and infrastructure, these fields are set to 0, or their information construction’s equal, reasonably than being solely faraway from the info construction. The complete adjustments to dam fields may be present in EIP-3675.

Subject Fixed worth Remark
ommers [] RLP([]) = 0xc0
ommersHash 0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347 = Keccak256(RLP([]))
problem 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) might be empty, and the hash of this record (ommersHash) will turn out to be the RLP-encoded hash of an empty record. Equally, as a result of problem and nonce are options of proof of labor, these might be set to 0, whereas respecting their byte-size values.

mixHash, one other mining-related area, gained’t be set to 0 however will as a substitute comprise the beacon chain’s RANDAO worth. Extra on this under.

BLOCKHASH & DIFFICULTY opcodes adjustments

Submit-merge, the BLOCKHASH opcode will nonetheless be accessible to be used, however given that it’ll not be solid via the proof of labor hashing course of, the pseudorandomness supplied by this opcode might be a lot weaker.

Relatedly, the DIFFICULTY opcode (0x44) might be up to date and renamed to PREVRANDAO. Submit-merge, it’s going to 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 might be saved within the ExecutionPayload the place mixHash, a worth related to proof of labor computation, was saved. The payload’s mixHash area may also 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 problem area within the block header. Submit-merge, the opcode, renamed to PREVRANDAO, factors to the header area which beforehand contained mixHash and now shops the prevRandao worth from the beacon chain state.

This variation, formalized in EIP-4399, additionally supplies on-chain functions a solution to assess whether or not The Merge has occurred. From the EIP:

Moreover, adjustments proposed by this EIP enable for good contracts to find out whether or not the improve to the PoS has already occurred. This may be executed by analyzing the return worth of the DIFFICULTY opcode. A worth better than 2**64 signifies that the transaction is being executed within the PoS block.

Block time

The Merge will influence the typical block time on Ethereum. Presently below proof of labor, blocks are available on common each ~13 seconds with a good quantity of variance in precise block instances. 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 follow, this at the moment occurs in <1% of slots.

This suggests a ~1 second discount of common block instances on the community. Sensible contracts which assume a selected common block time of their calculations might want to take this under consideration.

Protected Head & Finalized Blocks

Below proof of labor there’s at all times the potential for reorgs. Functions normally look forward to 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 a substitute have the ideas of finalized and secure head blocks. These blocks can be utilized much more 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 a minimum of 1/3 of the whole stake. On the time of this writing, this represents over $10 billion (or >2.5 million ETH) on Ethereum.

A secure head block is one which, below regular community situations, we count on to be included within the canonical chain. Assuming community delays of lower than 4 seconds, an trustworthy majority of validators and no assaults on the fork-choice rule, the secure head won’t ever be orphaned. A presentation detailing how the secure head is calculated below varied situations is accessible right here. Moreover, the assumptions and ensures of secure head are being formally outlined and analysed in an upcoming paper.

Submit-merge, execution layer APIs (e.g. JSON RPC) will expose the secure head utilizing a secure tag. Below regular community situations the secure head and the precise tip of the chain might be equal (with secure head trailing solely by just a few seconds). Protected heads might be much less prone to be reorged than the present proof of labor newest blocks.

Finalized blocks may also be uncovered by way of JSON RPC, by way of 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 Situations 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 a minimum of 1/3 to be slashed.

Be aware: the JSON RPC specification continues to be below energetic improvement. Naming adjustments ought to nonetheless be anticipated.

Subsequent Steps

We hope this put up helps utility builders put together for the much-anticipated transition to proof of stake. Within the subsequent few weeks, a long-lived testnet might 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 most recent technical updates about The Merge. See you there 👋🏻


Thanks to Mikhail Kalinin for offering the core content material of the “Protected Head” part and to Danny Ryan & Matt Garnett for reviewing drafts of this put up.

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