Transaction Base64 PSBT to Raw/Serialized Hex

In this article, we will consider the process of converting a base64-encoded PSBT (Programming Script Binaries) transaction into its raw and serialized (hex) formats. We will be using the Bitcoin Core CLI as our toolkit.

Prerequisites

• Familiarity with the basics of Bitcoin and its blockchain architecture.

• Understanding of PSBT and Base64 encoding standards.

Step 1: Convert Base64 PSBT transaction to Raw

To convert a base64-encoded PSBT transaction, we need to use the psbt command-line tool provided by Bitcoin Core. The converttopsbt command is used for this purpose. Here’s an example of how to use it:

bitcoincore-cli converttopsbt 

Replace with the actual base64 encoded PSBT transaction as shown in the Bitcoin Core output.

Step 2: Convert the raw transaction to serialized hex

After converting the PSBT transaction from raw format, we need to convert it to serialized (hex) format. We can again use a tool like psbt or use the cointool library for this purpose.

Here’s an example of how to convert a raw transaction from the Bitcoin Core CLI:

bitcoincore-cli cointool  -t raw2hex

Replace with the actual raw transaction as shown in the Bitcoin Core output.

Step 3: Compare and Check

To verify that the conversion process is correct, we can compare the base64-encoded PSBT transaction to its serialized (hexadecimal) equivalent:

bitcoincore-cli cointool  -t hex2raw

This command will create a raw transaction from the original transaction in base64 encoding.

Example Output

Here is an example output for the above steps using a fictitious PSBT transaction as input:

PSBT transaction in Base64 encoding
PSBT("1.3.0", {
"encoding": "base64",
"scriptSig": ["0101010000000000000000000000000000000000"],
"blockNumber": "100000",
"transactionIndex": "500000"
})

Conversion Code

Here’s a simple Python script to convert from base64 to raw and then serialize hex:

import base64
import json
def base64_to_tsb(base64_transaction):

Use the psbt command line tool, provided by Bitcoin Core
output = bitcoincore-cli converttopsbt(base64_transaction)
return json.loads(output)
def tsb_to_raw(tsb_json, encoding="base64"):

Use the cointool library to convert from raw to hex
if encoding == "raw":
return cointool(tsb_json, "hex2raw")
elif encoding == "hex":
return cointool(tsb_json, "hex2raw")

Usage example
base64_transaction = "PSBT(\"1.3.0\", { \"encoding\": \"base64\", \"scriptSig\":[\"010101000000000000000000000000000000\", \"blockNumber\": \"100000\", \"transactionIndex\": \"500000\" })"
tsb_json = base64_to_tsb(base64_transaction)
raw_hex = tsb_to_raw(tsb_json, encoding="hex")
print(raw_hex) 
Output: 

In this code example, we first convert a base64-encoded PSBT transaction to a Python dictionary using json.loads(). Then we use the cointool library to convert it from raw to hex. The result is output as raw and serialized (hex) transactions.

Conclusion

Converting between base64 and raw/serialized (hex) formats in Bitcoin Core involves two steps: first, converting a PSBT transaction from base64 to raw; secondly, converting the raw transaction into its serialized (hexadecimal) equivalent. This process can be implemented using various tools and libraries provided by the Bitcoin Core CLI.