Blocks

BlockHeader

name	type	size	description
producer	address	20	Address of block proposer committing this block.
previousBlockHash	bytes32	32	Previous block's header hash.
height	uint256	32	Block height.
blockNumber	uint256	32	Ethereum block number when this block is committed.
numTokens	uint256	32	Maximum token ID used through this block.
numAddresses	uint256	32	Maximum address ID used through this block
roots.length	uint16	2	Number of transaction roots.
roots	bytes32[]	32*	List of root header hashes.

Number of Tokens

Tokens IDs are registered contract-side to allow for more compact transactions. The maximum token ID used in this block and all previous blocks is included in the block header.

This is needed to prevent a griefing attack where a fraudulent rollup block is committed that spends a token ID that is not yet registered. The fraud proof can then be front-run with a transaction that registers the token ID, thereby invalidating the fraud proof.

See: token registry.

Number of Addresses

Address IDs are registered contract-side to allow for more compact transactions. The maximum address ID used in this block and all previous blocks is included in the block header.

This is needed to prevent a griefing attack where a fraudulent rollup block is committed that sends to an address ID that is not yet registered. The fraud proof can then be front-run with a transaction that registers the address ID, thereby invalidating the fraud proof.

See: address registry.

Roots

The block header includes a list of root header hashes, roots. Each individual root header hash is the hash of a root header, which commits to a list of transactions and other important metadata. For more information of why multiple roots are used instead of the more traditional single-transactions-root, see Block Architecture.

The number of root header hashes is upper-bounded by the TRANSACTION_ROOTS_MAX parameter (128).

Committing a New Block Header

When a new block header is produced and committed to Ethereum, the following checks must pass, and are enforced by the smart contract.

1. The height blockHeight must be greater than 0 and at most the tip height.
2. The previous block hash previousBlockHash must match the previous block hash at blockHeight.
3. The number of transaction roots roots.length must be greater than 0 and at most TRANSACTION_ROOTS_MAX.
4. Every root in roots must exist in the root registry.
5. If the operator is not in penalty mode (discussed below):
   1. If the block producer producer is not the operator:
      1. At least the submission delay parameter Ethereum blocks must have elapsed since the root was submitted.

The penalty mode becomes active if a successful fraud proof against an operator-produced block is processed. It remains active for the penalty delay parameter Ethereum blocks.