Blockchain – Understanding Block Header Format

block-headerblocksleveldbrlp

Does anyone understand what each element of a block header represents? I have an example block header represented here:

[

cd7bd64fba4cc782fe5474d3640882afece5887180591e72f80ce6916cf73526,

1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347,

f927a40c8b7f6e07c5af7fa2155b4864a4112b13,

30430d24554454b251003be3d027dea94397bf45cd34c6a06abcfec662242046,

56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421,

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000,

3b32b8463f,

1780,

1388,

"",

55ba9f2d,

"Geth/v1.0.0/linux/go1.4.2",

437fa41b15c73334a947241ec885423a487d4401a0c3ec7c30550c1e039bccd7,

c5317acb884dfc49,

]

What do each of these elements represent? Is there an official source that also definitively says what each of these values mean?

Best Answer

Parent hash: This is the Keccak 256-bit hash of the parent (previous) block's header.

• Ommers hash: This is the Keccak 256-bit hash of the list of ommers (or uncles) blocks included in the block.

• The beneficiary: The beneficiary field contains the 160-bit address of the recipient that will receive the mining reward once the block is successfully mined.

• State root: The state root field contains the Keccak 256-bit hash of the root node of the state trie. It is calculated once all transactions have been processed and finalized.

• Transactions root: The transaction root is the Keccak 256-bit hash of the root node of the transaction trie. The transaction trie represents the list of transactions included in the block.

• Receipts root: The receipts root is the Keccak 256-bit hash of the root node of the transaction receipt trie. This trie is composed of receipts of all transactions included in the block. Transaction receipts are generated after each transaction is processed and contain useful post-transaction information. More details on transaction receipts are provided in the next section.

• Logs bloom: The logs bloom is a bloom filter that is composed of the logger address and log topics from the log entry of each transaction receipt of the included transaction list in the block. Logging is explained in detail in the next section.

Logs bloom: The logs bloom is a bloom filter that is composed of the logger address and log topics from the log entry of each transaction receipt of the included transaction list in the block. Logging is explained in detail in the next section.

• Difficulty: The difficulty level of the current block.

• Number: The total number of all previous blocks; the genesis block is block zero.

• Gas limit: This field contains the value that represents the limit set on the gas consumption per block.

• Gas used: This field contains the total gas consumed by the transactions included in the block.

• Timestamp: The timestamp is the epoch Unix time of the time of block initialization.

Extra data: The extra data field can be used to store arbitrary data related to the block. Only up to 32 bytes are allowed in this field.

• Mixhash: The mixhash field contains a 256-bit hash that, once combined with the nonce, is used to prove that adequate computational effort (Proof of Work, or PoW) has been spent in order to create this block.

• Nonce: Nonce is a 64-bit hash (a number) that is used to prove, in combination with the mixhash field, that adequate computational effort (PoW) has been spent in order to create this block.

Related Solutions

Ethereum – Understanding Block Structure, Roots, and Tries Concept

Firstly, you'll want to take a look at this picture from a previous question for reference.

Q1 - Where does geth stores these tries - I reckon within the block themselves, i.e. chaindata folder, within the ldb files? Or am I entirely off-base?

The chain data isn't actually part of the block proper - it's stored separately in a leveldb database. On your machine this is what's inside the chaindata folder. The block itself stores the hashes of the roots of the various tries, the state data (i.e. chain data) being one of these.

See:

Q2 - (I am assuming the state trie is indeed kept in each block) Does the state trie of block N references the state trie of block N-1 (if no changes to an account's state is found, i.e. only log accounts with differences), or is the state trie duplicated across blocks?

Your first assumption isn't correct, as per Q1, but yes, the state trie references backwards to prevent duplication. This picture from this previous answer helps visualise this:

Q3 - While state tree pruning, I reckon that the states are pruned off since if we have the stateRoot, this effectively verifies that the state trie nodes are OK, hence safe to discard the state trie themselves - Would this understanding be correct from high level perspective?

I'm not entirely sure, but this previous official blog post might help: https://blog.ethereum.org/2015/06/26/state-tree-pruning/

Q4 - What would the .\ethereum\nodes folder be for?

It's a database of nodes your node knows about. It's blobified in RLP format, so it's not readily readable. For further details, see Format of LevelDB files in nodes directory? Trouble pulling contents with python leveldb API

[Ethereum] block-header hash verification

Below are the steps to calculate blockHash, given a blockNumber:

Step1. eth.getBlock(400000)

Output:{ difficulty: '6022643743806', extraData: '0xd583010202844765746885676f312e35856c696e7578', gasLimit: 3141592, gasUsed: 0, hash: '0x5d15649e25d8f3e2c0374946078539d200710afc977cdfc6a977bd23f20fa8e8', logsBloom: '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000', miner: '0x2a65Aca4D5fC5B5C859090a6c34d164135398226', mixHash: '0x3fbea7af642a4e20cd93a945a1f5e23bd72fc5261153e09102cf718980aeff38', nonce: '0x6af23caae95692ef', number: 400000, parentHash: '0x1e77d8f1267348b516ebc4f4da1e2aa59f85f0cbd853949500ffac8bfc38ba14', receiptsRoot: '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421', sha3Uncles: '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347', size: 539, stateRoot: '0x0b5e4386680f43c224c5c037efc0b645c8e1c3f6b30da0eec07272b4e6f8cd89', timestamp: 1445130204, totalDifficulty: '2014130882275463845', transactions: [], transactionsRoot: '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421', uncles: [] }

Hash in the above object refers to the blockHash which we are trying to validate. This is the actual output which will be used later to compare the test results with.

Step2. Remove some of the elements from the above object, keep only those that are inputs into a blockHeader, and reorder it as below:

[['ParentHash','0x1e77d8f1267348b516ebc4f4da1e2aa59f85f0cbd853949500ffac8bfc38ba14'], ['UncleHash','0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347'], ['Coinbase','0x2a65Aca4D5fC5B5C859090a6c34d164135398226'], ['Root','0x0b5e4386680f43c224c5c037efc0b645c8e1c3f6b30da0eec07272b4e6f8cd89'], ['TxHash','0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421'], ['ReceiptHash','0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421'], ['Bloom','0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'], ['Difficulty',6022643743806], ['Number','0x400000'], ['GasLimit',3141592], ['GasUsed',0], ['Time',1445130204], ['Extra','0xd583010202844765746885676f312e35856c696e7578'], ['MixDigest','0x3fbea7af642a4e20cd93a945a1f5e23bd72fc5261153e09102cf718980aeff38'], ['Nonce','0x6af23caae95692ef']]

Step3. Convert values with numbers to Hex

console.log(web3.utils.toHex(gasLimit));
console.log(web3.utils.toHex(gasUsed));
console.log(web3.utils.toHex(time));
console.log(web3.utils.toHex(difficulty));
console.log(web3.utils.toHex(number));

Step4. For elements with value as 0, use 0x and not 0x0

Example: for block 400000, the value for gasUsed is 0. So the value used for gasUsed should be 0x and not 0x0

Step5. After changing the numbers to Hex and handing values with 0, we can go ahead and remove all the keys listed in Step2 and restructure the array as below:

[ '0x1e77d8f1267348b516ebc4f4da1e2aa59f85f0cbd853949500ffac8bfc38ba14', '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347', '0x2a65aca4d5fc5b5c859090a6c34d164135398226', '0x0b5e4386680f43c224c5c037efc0b645c8e1c3f6b30da0eec07272b4e6f8cd89', '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421', '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421', '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000', '0x57a418a7c3e', '0x61a80', '0x2fefd8', '0x', '0x5622efdc', '0xd583010202844765746885676f312e35856c696e7578', '0x3fbea7af642a4e20cd93a945a1f5e23bd72fc5261153e09102cf718980aeff38', '0x6af23caae95692ef' ]

Step6. The above array of values can now be fed into a rlp.encode function

Output: 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

Step7. Pass the above RLP through a keccak256 function. Below is the output:

TestOutput: 0x5d15649e25d8f3e2c0374946078539d200710afc977cdfc6a977bd23f20fa8e8

ActualOutput: 0x5d15649e25d8f3e2c0374946078539d200710afc977cdfc6a977bd23f20fa8e8

Conclusion: Use eth.getBlock(). Take the object it returns as output. Remove unwanted elements and keep only those that are inputs to a blockHeader. Convert numbers to Hex and handle values with 0s. Restructure the object to form an array of strings. Pass this array into a rlp.encode function. Take the rlp output and apply a keccak256 hash on it.

Links: https://github.com/ethereum/go-ethereum/blob/master/core/types/block.go#L69

Best Answer

Related Solutions

Ethereum – Understanding Block Structure, Roots, and Tries Concept

[Ethereum] block-header hash verification

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