Scroll Upgrades

As the team continues to progress on Scroll’s roadmap, we will be upgrading the Scroll network to include new features and improvements.

The following contracts are used to initiate upgrades and execute upgrades after the two-week timelock period:

Contract	Network	Address
L1 Scroll Multisig	Ethereum	`0xEfc9D1096fb65c832207E5e7F13C2D1102244dbe`
L1 Timelock	Ethereum	`0x1A658B88fD0a3c82fa1a0609fCDbD32e7dd4aB9C`
L2 Scroll Multisig	Scroll	`0xEfc9D1096fb65c832207E5e7F13C2D1102244dbe`
L2 Timelock	Scroll	`0xf6069DB81239E5194bb53f83aF564d282357bc99`

You can join our Telegram channel for technical updates, which includes future upgrade announcements and on-chain operation events.

During internal testing, we identified that blocks may not always be compressible under certain conditions, which leads to unprovable chunks and batches. To fix this issue, a minor upgrade has been conducted so that uncompressed blobs will be enabled when this special case is detected.

Timeline

As this is a security related patch, we bypassed the 7-day timelock mechanism.

Scroll Sepolia: August 28th, 2024
Scroll Mainnet: September 2nd, 2024

Compatibility

Sequencer and Follower Nodes (l2geth)

The new node version is v5.7.0. See the release notes for more information.

This upgrade does not change Scroll’s state transition function, so it is backward compatible. However, the format of the batch data committed to Ethereum changes. As a result, nodes that enabled rollup verification (--rollup.verify) must upgrade to be able to follow the chain.

Dapps and Indexers

A change has been implemented to Scroll Mainnet to enhance sequencer throughput, which adjusted the maximum reorg depth to 17 blocks. Previously, the system performed thorough capacity checks within the signer thread to determine whether transactions exceed the circuit limit. While this ensures that all transactions within a block are compliant, it also requires additional CPU resources. We introduced a new circuit capacity checking scheme on Mainnet. The sequencer thread now will continue to perform capacity checks, but in a more approximate manner. In parallel, 16 worker threads will accurately verify the capacity of previous blocks. As a result, a reorg could occur with a maximum depth of 17 blocks, although the likelihood of this is low.

For indexers, the BatchHeader version has been upgraded to 4. This is backward compatible (the only exception is for developers decoding the blob payload, which has changed slightly).

Darwin Upgrade

Overview

This upgrade will reduce gas fees by 34% by using a single aggregated proof for multiple batches, eliminating the need to finalize each batch individually.

Darwin uses a new V3 batch codec.
In addition to the previous notions of chunk and batch, we have introduced a new concept called bundle.
- Chunk: A unit of zkEVM proving, consisting of a list of L2 blocks.
- Batch: A collection of chunks encoded into one EIP-4844 blob, serving as the unit of Data Availability.
- Bundle: A series of batches that functions as the unit of finalization.
The main difference compared to Curie is that Scroll will now finalize multiple batches using a single aggregated bundle proof.
The on-chain bundle proof verifier uses a new public input layout.

Timeline

Scroll Sepolia
- Network Upgrade: August 14th, 2024
Scroll Mainnet
- Upgrade Initiation: August 5th, 2024
- Timelock Completion & Upgrade: August 21st, 2024

Technical Details

Contract Changes

Note: Since the previous Curie upgrade, we have migrated the Scroll contracts to a new repo at scroll-contracts.

The code changes for this upgrade are implemented in this PR. The key changes are as follows:

We have introduced a new BatchHeaderV3Codec.
We have changed how messages are processed in the L1MessageQueue contract. Prior to Darwin, we would process messages when a batch is finalized. After Darwin, most of this processing is moved to the commit step.
We have introduced a new public input format for bundle proofs. This is implemented in a new contract IZkEvmVerifierV2, which is in turn added to MultipleVersionRollupVerifier.
In the ScrollChain contract version=3 batches will now be committed through a new function called commitBatchWithBlobProof. Bundles will be finalized using a new function called finalizeBundleWithProof.

See the contract release notes for more information.

Node Changes

The new node version is v5.6.0. See the release notes for more information.

The main changes are:

Implementation of timestamp-based hard forks.
Processing V3 batch codec in rollup-verifier.

zkEVM circuit changes

The new version of zkevm circuits is v0.12.0. See here for the release log.

We have introduced a RecursionCircuit that will bundle multiple sequential batches by recursively aggregating the SNARKs from the BatchCircuit (previously AggregationCircuit). The previously 5 layer proving system is now 7 layers as we introduce:

6th Layer (layer5): RecursionCircuit that recursively aggregates BatchCircuit SNARKs.
7th Layer (layer6): CompressionCircuit that compresses the RecursionCircuit SNARK and produce an EVM-verifiable validity proof.

The public input to the BatchCircuit is now context-aware of the “previous” batch, which allows us to implement the recursion scheme we adopted (described here in-depth).

Audits

TrailofBits: coming soon!

Compatibility

Sequencer and Follower Nodes (l2geth)

This upgrade does not alter the state transition function and is therefore backward-compatible. However, we strongly recommend node operators to upgrade to v5.6.0.

Dapps and Indexers

There are some major changes to how we commit and finalize batches after Darwin.

Batches will be encoded using the new V3 batch codec. This version adds two new fields:
1. lastBlockTimestamp (the timestamp of the last block in this batch).
2. blobDataProof (the KZG challenge point evaluation proof).
This version removes skippedL1MessageBitmap. There will be no changes to how the blob data is encoded and compressed.

Batches will be committed using the commitBatchWithBlobProof function (instead of the previous commitBatch).

New function signature:

function commitBatchWithBlobProof(uint8 _version, bytes calldata _parentBatchHeader, bytes[] memory _chunks, bytes calldata _skippedL1MessageBitmap, bytes calldata _blobDataProof)

Batches will be finalized using the finalizeBundleWithProof function (instead of the previous finalizeBatchWithProof4844).

New function signature:

function finalizeBundleWithProof(bytes calldata _batchHeader, bytes32 _postStateRoot, bytes32 _withdrawRoot, bytes calldata _aggrProof)

The semantics of the FinalizeBatch event will change: It will now mean that all batches between the last finalized batch and the event’s _batchIndex have been finalized. The event’s stateRoot and withdrawRoot values belong to the last finalized batch in the bundle. Finalized roots for intermediate batches are no longer available.

The semantics of the CommitBatch and RevertBatch events will not change.

Recommendations:

Indexers that decode committed batch data should be adjusted to use the new codec and the new function signature.
Indexers that track batch finalization status should be adjusted to consider the new event semantics.

Curie Upgrade

Overview

This significant upgrade will reduce gas fees on the Scroll chain by 1.5x. Highlights include:

Compresses the data stored in blobs using the zstd algorithm. This compression reduces the data size, allowing each blob to store more transactions, thereby reducing data availability cost per transaction.
Adopts a modified version of the EIP-1559 pricing model which is compatible with the EIP-1559 transaction interface, bringing beneftis such as more accurate transaction pricing and a more predictable and stable fee structure.
Support for new EVM opcodes TLOAD, TSTORE, and MCOPY. Users can safely use the latest Solidity compiler version 0.8.26 to build the contracts.
Introduces a dynamic block time. During periods of traffic congestion, a block will be packed when the number of transactions reaches the circuit limit instead of waiting for the 3-second interval.

Timeline

Scroll Sepolia
- Network Upgrade: June 17th, 2024
Scroll Mainnet
- Upgrade Initiation: June 20th, 2024
- Timelock Completion & Upgrade: July 3rd, 2024

Technical Details

Contract Changes

The code changes for this upgrade are documented in the following PRs:

The main changes are as follows:

The rollup contract (ScrollChain) will now accept batches with both versions 1 and 2. Version 1 is used for uncompressed blobs (pre-Curie), while version 2 is used for compressed blobs (post-Curie).
The L1GasPriceOracle contract will be updated to change the data fee formula to account for blob DA, providing a more accurate estimation of DA costs:
- Original formula: (l1GasUsed(txRlp) + overhead) * l1BaseFee * scalar
- New formula: l1BaseFee * commitScalar + len(txRlp) * l1BlobBaseFee * blobScalar

Node Changes

The new node version is v5.5.0. See the release notes for the list of changes.

zkEVM circuit changes

The new version of zkevm circuits is v0.11.4. See here for the release log.

Audits

TrailofBits: coming soon!
Zellic

Compatibility

Sequencer and Follower Nodes (l2geth)

This upgrade is a hard fork, introducing the TLOAD, TSTORE, and MCOPY opcodes. Operators running an l2geth node are required to upgrade before the hard fork block. For more information, see the node release note.

Dapps and Indexers

For dApps, this upgrade is backward compatible. Developers should adjust the gas fee settings to incorporate the EIP-1559 pricing model. Note that dApps can no longer rely on the fixed 3-second block time in the application logic.

For indexers, the data format remains the same. The will be however changes to the data content:

The version field in BatchHeader will be changed to 2 since Curie block.
The data stored in blob will be compressed and can be decompressed by zstd v1.5.6.

Bernoulli Upgrade

Overview

This upgrade features a significant reduction in transaction costs by introducing support for EIP-4844 data blobs and supporting the SHA2-256 precompile.

Timeline

Scroll Sepolia
- Network Upgrade: April 15th, 2024
Scroll Mainnet
- Upgrade Initiation: April 15th, 2024
- Timelock Completion & Upgrade: April 29th, 2024

Technical Details

Contract changes

The contract changes for this upgrade are in this PR, along with the audit fixes here. The main changes are as follows:

ScrollChain now accepts batches with either calldata or blob encoding in commitBatch.
ScrollChain now supports finalizing blob-encoded batches through finalizeBatchWithProof4844.
MultipleVersionRollupVerifier can now manage different on-chain verifiers for each batch encoding version.

Node changes

The new node version is v5.3.0. See here for the release log.

zkEVM circuit changes

The new version of zkevm circuits is v0.10.3. See here for the release log.

Audits

Compatibility

Sequencer and follower nodes (l2geth)

This upgrade is a hard fork as it introduces the new blob data type and the SHA2-256 precompiled contract. Operators running an l2geth node are required to upgrade before the hard fork block. See the node releases for more information.

Indexers and Bridges

This upgrade changes the format that Scroll uses to publish data to Ethereum. Projects that rely on this data should carefully review the new data format, and check whether their decoders need to be adjusted. A summary of the new format:

The format of BlockContext will not change.
Chunks will no longer include the L2 transaction data. This will instead be stored in a blob attached to the commitBatch transaction.
BatchHeader now contains one new field, BlobVersionedHash.

Provers

This upgrade involves a breaking change in zkevm-circuits. Operators running a prover node are required to upgrade.

Bridge Upgrade

Overview

To reduce bridging costs, we implemented several gas optimizations on our bridge and rollup contract suite. The optimization techniques used include the following:

We will now use constants to store some companion contract addresses, instead of using storage variables. This is possible since these values should (almost) never change. With this change we can save on a few storage load operations.
We updated the intrinsic gas estimation in L1MessageQueue to use a simple upper bound instead of an exact calculation. The two results will be similar for most bridge transactions but the new implementation is significantly cheaper.
We merged two contracts L1MessageQueue and L2GasPriceOracle to save on call costs from one contract to the other.

Timeline

Scroll Sepolia:
- Network Upgrade: January 19, 2024
Scroll Mainnet:
- Upgrade Initiation: February 7, 2024
- Timelock Completion & Upgrade: February 21, 2024

Technical Details

Code Changes

Bridge Cost Optimization
Audit Fixes
Previously deployed version (commit ff380141a8cbcc214dc65f17ffa44faf4be646b6)
Version deployed (commit 6030927680a92d0285c2c13e6bb27ed27d1f32d1)

Audits

OpenZeppelin

List of Changes

Changes to L1 contracts:

In ScrollChain, change messageQueue and verifier to immutable.
In L1ScrollMessenger, change counterpart, rollup, and messageQueue to immutable.
In all token gateways, change counterpart, router, and messenger to immutable.
Merge L1MessageQueue and L2GasPriceOracle into a single contract L1MessageQueueWithGasPriceOracle (deployed on the same address as the previous L1MessageQueue). In this contract, we also change messenger and scrollChain to immutable, and simplify calculateIntrinsicGasFee.

Changes to L2 contracts:

In L2ScrollMessenger, change counterpart to immutable.
In all token gateways, change counterpart, router, and messenger to immutable.

Contracts affected:

L1: L1MessageQueue, L2GasPriceOracle, ScrollChain, L1WETHGateway, L1StandardERC20Gateway, L1GatewayRouter, L1ScrollMessenger, L1CustomERC20Gateway, L1ERC721Gateway, L1ERC1155Gateway.
L2: L2ScrollMessenger, L2WETHGateway, L2StandardERC20Gateway, L2GatewayRouter, L2CustomERC20Gateway, L2ERC721Gateway, L2ERC1155Gateway.

The original gas price oracle contract will be deprecated: it will no longer be updated or used by the Scroll bridge.

Ethereum:
- L2GasPriceOracle: 0x987e300fDfb06093859358522a79098848C33852
- L1MessageQueueWithGasPriceOracle: 0x0d7E906BD9cAFa154b048cFa766Cc1E54E39AF9B
Sepolia:
- L2GasPriceOracle: 0x247969F4fad93a33d4826046bc3eAE0D36BdE548
- L1MessageQueueWithGasPriceOracle: 0xF0B2293F5D834eAe920c6974D50957A1732de763