Hash-Preimage Construction in Two-Peak Hashing for Two-Piece Transaction Verification
In the context of Bitcoin’s transaction verification process, a critical step involves constructing a hash-preimage that can be used to create signatures. This process is essential for ensuring the integrity and authenticity of transactions. In this article, we will delve into how Bitcoin nodes construct hashes for two-piece input transactions using the two-peak hashing method.
Overview of Two-Peak Hashing
Two-peak hashing is a variant of the standard hashing algorithm used in Bitcoin to create signatures. It was introduced as an alternative to the traditional Merkle tree-based signature verification process. The two-peak hashing method uses a hierarchical hash function to derive a key for each transaction, which can then be used to verify signatures.
Hash Construction
To construct a hash-preimage, we need to serialize each input’s private key and public key. Here’s an overview of the steps involved:
- Serialize the private key (
vps) and public key (vp).
- Concatenate these serialized values with the transaction hash (
txh).
The resulting concatenated value is then used as a single hash input for the two-peak hashing algorithm.
def construct_hash_preimage(private_key, public_key, txh):
Concatenate private and public keys with transaction hash
concatenated = f"{private_key}{public_key}{txh}"
Use the concatenated value as an input to the two-peak hashing function
return hashlib.sha256(concatenated.encode()).hexdigest()
- Double-hash the constructed hash-preimage.
Once we have a double-hash of our hash-preimage, we need to verify that it matches the expected signature for each input in the transaction.
def verify_signature(hash_preimage, sig, txid):
Find the index of the first input with matching private key
idx = hash_preimage[:txid]
Double-hash the index and compare it to the given signature
double_hash = hashlib.sha256(idx.encode()).hexdigest()
return double_hash == sig
Verification Process
To verify a transaction, Bitcoin nodes rebuild the hash-preimages for each input using the constructed hash function. Then, they double-hash these preimages and compare them to the provided signatures.
def verify_transaction(tx):
Rebuild hash-preimages for all inputs in the transaction
hashes = {}
for (i, txid), (private_key, public_key) in enumerate(tx.inputs):
hash_preimage = construct_hash_preimage(private_key, public_key, txh[i])
Double-hash the preimage and verify it against the signature
verified = verify_signature(hash_preimage, txid, txid)
if not verified:
raise ValueError("Invalid transaction")
return True
All inputs are correctly rebuilt and verified
By following this process, Bitcoin nodes ensure that transactions are validated accurately and efficiently. The use of two-peak hashing provides a secure method for generating signatures and verifying hashes in the context of Bitcoin’s verification protocol.
Conclusion
In conclusion, constructing hash-preimages using two-peak hashing is an essential step in ensuring the integrity and authenticity of Bitcoin transactions. By following this process, nodes can rebuild the required hash inputs to verify signatures and validate transactions accurately. This methodology provides a secure and efficient way to handle complex transactions in the Bitcoin network.
Note: This article assumes that you have a basic understanding of Bitcoin’s transaction verification protocol and the two-peak hashing algorithm. If you’re new to Bitcoin, it is recommended to consult additional resources or seek guidance from an experienced developer.
