> For the complete documentation index, see [llms.txt](https://docs.zkopru.network/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zkopru.network/how-it-works/block.md).

# Block structure & serialization

A zkopru block is submitted to the layer1 in a serialized form. Then, the checksum of the proposal becomes the proposal ID and is used for the challenge system.

## Block structure

The zkopru block includes a header and a body.

![Block details](/files/-MBY98CR5Eta1cyRQTbu)

Edit diagram here

## Header

The first 340 bytes of the data should be the block header. The block header contains the following data:

| Property                            | type    |
| ----------------------------------- | ------- |
| Proposer's address                  | address |
| Parent block hash                   | bytes32 |
| Fee                                 | uint256 |
| Latest UTXO tree's root             | uint256 |
| Latest UTXO tree's leaf index       | uint256 |
| Nullifier tree's root               | bytes32 |
| Latest withdrawal tree's root       | uint256 |
| Latest withdrawal tree's leaf index | uint256 |
| Transactions' root                  | bytes32 |
| Deposits' root                      | bytes32 |
| Migrations' root                    | bytes32 |

## Body

A block body consists of transactions, mass deposits, and mass migrations. Moreover, the block header should contain correct information from the body. If the header does not have the correct value, the proposer will get slashed through the challenge system.

### Transactions

![Tx serialization](/files/-MBcikJp6pZDYJ2XrVjw)

### Mass deposits

![](/files/-MBciqV9Y1e0u71yjYfo)

### Mass migrations

![](/files/-MBcixTcJHqkEHWu-wsM)


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