Decrypting the Raw ScriptOutput: Extracting the ScriptPubKey
If you are using zeroMQ to receive transactions from Bitcoin Core, you are probably dealing with the raw script output in JSON format. The “script” field contains a serialized version of a Bitcoin script, which we need to extract the “scriptPubKey”. This type represents the public key that can be used for digital signatures and other cryptographic operations.
In this article, we will look at how to extract the scriptpubkey (the actual bytes that represent the public key) from the raw script output.
Understanding Bitcoin Script Format
Before we dive into the code, let’s quickly look at the format of a Bitcoin script. The “script” field in Bitcoin Core transactions typically consists of a serialized version of the following:
OP_DUP: duplicates the current operand (in this case, the value)
OP_P2PKH: indicates that these are private keys
OP_D2SH: converts the script to a human-readable format
- … and so on
The output of the raw script typically looks like this:
{value: 200000,
script: }
Decode script output
To get “scriptPubKey” , we need to decode the raw output of the script. As an example, we can use the following Python code snippet:
“` Python
JSON import
on def extract_scriptpubkey(script output):
Split the script into individual elements
elements = script output[‘script’].split(‘\x00’)
Initialize the scriptpubkey variable
script_pubkey = None
Iterate over each element and try to decode it as a script signature
for element in elements:
if element.startswith(‘OP_DUP’):
Extract the value of the duplicate operand (input)
value = int.from_bytes(element[7:9], byteorder=’large’)
Check if this is an OP_P2PKH instruction with a private key
if ‘P2SH’ in element and ‘OP_01’ in element:
Extract the public Key from input (assuming it is based on 1 indexing)
public key = int.from_bytes(element[9:16], byte order=’large’)
Set the scriptpubkey variable with the extracted public key
if script_pubkey is None:
script_pubkey = bytes([public_key])
else:
script_pubkey += bytes([public_key])
elif ‘P2SH’ in element and ‘OP_01’ in element:
Extract the public key from input (assuming it is based on 1 indexing)
public key = int.from_bytes(element[9:16], byte order=’large’)
Set the scriptpubkey variable to a dummy value for the OP_DUP statement
if script_pubkey is None:
script_pubkey = bytes([public_key])
else:
script_pubkey += bytes([public_key])
elif ‘OP_01’ in element:
Extract the public key from the input (assuming it is based on 1 indexing)
public_key = int.from_bytes(element[8:16], byte_order=’large’)
Set the scriptpubkey variable to a dummy value for the OP_DUP statement
if script_pubkey is None:
script_pubkey = bytes([public_key])
else:
script_pubkey += bytes([public_key])
return script_pubkey
Example usage
script_output = json.loads(‘{“value”: 200000, “script”: “
script_pubkey = script_pubkey extraction (script_output)
print (script_pubkey.