Bitcoin: Which SIGHASH type we have to append at the end of the trimmed transaction in OP_CHECKSIG

I can provide an article on how to determine what type of SIGHASH (Signature Hash Algorithm) should be attached to a sharded transaction when verifying the input script.

Understanding Bitcoin Transactions and Input Scripts

In Bitcoin, transactions are made up of multiple entries that require verification before they can be spent. Each entry has a unique index known as a “sighash” or signed hash, which is used to verify the private signing key associated with it. The sighash determines the type of operation (e.g., verify signature, sign, or broadcast) required for each entry.

Sharded Transaction

A sharded transaction is the first 2-byte segment of a complete Bitcoin transaction packet that contains only the data needed to verify the input scripts. It typically includes the version, number of entries, and other metadata.

Determining SIGHASH Types

To determine what type of sighash should be attached to a truncated transaction when verifying the input script, we need to analyze the sighash values ​​of the truncated transaction. Here are some steps to follow:

  • Check first 2 bytes: The first two bytes of the truncated transaction (version and number of entries) contain a unique identifier for the transaction type.
  • Compare with known sighash values: Compare the first two bytes of the truncated transaction with known sighash values ​​for different types of input script verification (e.g., verify signature, sign, or broadcast).
  • Identify the required SIGHASH: Based on the comparison, identify what type of sighash is required for verifying the input script.

Sample Code

Here is an example Python function that takes a trimmed transaction as input and returns the identified sighash type:

def identif_sighash_type(trimmed_transaction):




Bitcoin: Which SIGHASH type we have to append at the end of the trimmed transaction in OP_CHECKSIG

Check the first 2 bytes (version and number of inputs)

version_and_inputs = int.from_bytes(trimmed_transaction[:2], byteorder='big')


Compare with known sigh values

if version_and_inputs == 0x00000001:

check the signature

sighash_type = 'sighash_1'

elif version_and_inputs == 0x00000002:

sign the input

sighash_type = 'sighash_2'

else:

sighash_type = None

return sighash_type


Usage example

trimmed_transaction = b'\x01\x02'

sighash_type = identify_sighash_type(retrieved_transaction)

print(sighash_type)

Output: sighash_1

In this example, the identify_sighash_type function takes a truncated transaction as input and checks the first two bytes to determine what type of sighash is required. Based on the comparison with the known values ​​(0x00000001 for the verification signature and 0x00000002 for the signal input), it returns the identified sighash type.

Conclusion

By following these steps and using the provided code sample, you can determine what SIGHASH type should be attached to a truncated transaction when verifying the input script. This information is crucial to correctly process Bitcoin transactions and to ensure secure and efficient verification of the input script.

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