Ethereum: How is a transaction ID generated and when does it change? (with a new sequence ID?)
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Understanding Ethereum Transaction Identifiers
As a developer building a custom Ethereum client, you’re probably familiar with the concept of Transaction Identifiers (TxIDs) on the Ethereum blockchain. In this article, we’ll take a look at how these unique identifiers are generated and what happens to them after each block.
Generating Transaction Identifiers
A transaction identifier is an 18-byte hexadecimal string that represents a unique Bitcoin transaction. The generation process involves several steps:
- Block creation: A new block is created on the Ethereum network when a valid transaction is sent to the network.
- Transaction hash: Each transaction in a block is hashed using the “sha256” algorithm with the block hash as input and the Merkle root of all transactions as additional inputs.
- Transaction ID Generation: The transaction hash is then used to generate a unique 18-byte hexadecimal string called the Transaction ID (TxID).
The TxID is generated in two parts:
- Block Digest: This is the actual hash of the block, which is a combination of the block header and other metadata.
- Merkle Root
: This is an additional input parameter to the transaction hashing algorithm that helps ensure uniqueness and integrity.
TxID Generation Algorithm
The Ethereum community has developed a consensus algorithm called “Keccak-256” to generate transaction IDs. The algorithm takes two inputs:
- Block Digest: This is the actual hash of the block.
- Merkle Root: This is an additional parameter to calculate the Merkle Root.
The resulting TxID is generated using a combination of the block hash and the Merkle root, resulting in an 18-byte hexadecimal string.
When will this change?
When each block is created on the Ethereum network, the transaction ID of that block changes. This change happens because each new block in the chain has its own unique transaction hash and Merkle root.
To illustrate this concept, let’s look at the following example:
- Block 1: A new block is created with a special block hash (e.g. “0x1234567890abcdef”).
- Transaction hashes: Each of the 10 transactions in block 1 has its own unique transaction hash, created using the Keccak-256 algorithm.
- Merkle rings: A Merkle root for each of these transactions is also generated.
Therefore, as we create new blocks on the Ethereum network, they will have their own unique block hashes and Merkle roots, which will cause changes to the transaction identifiers associated with those blocks.
Example use case:
To illustrate how this process works, let’s look at a Python example:
import hashlib
import json
def generate_txid(block_hash):
Hash function used for Keccak-256def hash_function(input_string):
return hashlib.sha256(input_string.encode()).hexdigest()
block_merkle_root = hash_function(str(block_hash))
transaction_hashes = []
for i in range (10):
assuming 10 transactionstxid = hash_function(json.dumps(i, sort_keys=True)) + block_merkle_root
transaction_hashes.append(txid)
return json.dumps(transaction_hashes), block_merkle_root
block_hash = "0x1234567890abcdef"
txids, merkle_root = generate_txid(block_hash)
print("Transaction hashes:", txids)
print("Merkle root:", merkle_root)
In this example, we create a new block hash using the hash_function function. We then use this block hash as input to the transaction hashing algorithm and store the resulting TxID along with the Merkle root.
This process ensures that each new block on the Ethereum network has its own unique transaction ID and Merkle code, which causes changes to the transaction IDs associated with those blocks.
Conclusion
Understanding how transaction identifiers are generated and modified is crucial to building a reliable and efficient custom Ethereum client.
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