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Ethereum: A Step-by-Step Guide to Manually Signing Bitcoin Transaction

In this tutorial, we’ll walk you through the process of creating a manually signed Bitcoin transaction with one input and two outputs, including one for change and one OP_RETURN (Output Program Return) anchor data. We’ll also use our popular Regtest backend to test out our creation.

The Raw Unprocessed Transaction

A Bitcoin transaction is typically processed in a series of blocks, which are grouped into a batch called a “block”. Each block contains multiple transactions, including inputs and outputs. In this example, we have one input and two outputs: one for change and one OP_RETURN anchor data.

Here’s the raw unsigned transaction:

0000000000000000000000000000000000000000000000000000000000000000000000000000


012345678901234567890123456789012345678901


010101010101010101010101010101 0101010101010101010101


020202020202020202020202020202020202020202020202020


03030303030303030303030303030303030303


04040404040404040404040404040404040404


0505050505050505050500 5050505050505


06066006066006066006066006066006


07070707070707070707070707070707


080808080808080808080808080


09090909090909090909090909090909


1001010101010101010101010


1101 111101111101111101011111


12012112012112012121


13013113013113013113


14014144014144014


15015155015155


16016160016161


17017170171717


18018118018118


19019

The Manual Signing Process

To manually sign the transaction, we’ll need to:

  • Create a new unsigned transaction with two inputs: one for change and one OP_RETURN anchor data.

  • Add the input transactions to the block header.

  • Add the output transactions (including the change output).

  • Sign the entire transaction using our private key.

Here’s an example of how we could create and sign this transaction manually:

// Define our inputs and outputs


unsigned char* input1 = "00000";


unsigned char* input2 = "0000";


unsigned char* outputChange = "12345678901234567890123456789";


unsigned char* op_returnAnchor = "op_return_anchor";




// Create the transaction header with two inputs


unsigned char* txHeader = new unsigned char[64];


txHeader[0] = 1; // Signature field (length)


txHeader[1] = 2; // Signature


txHeader[2] = 3;


txHeader[3] = 4;


txHeader[4] = 5;




// Add the input transactions to the block header


unsigned char* inputs[] = {input1, input2};


unsigned int numInputs = 2;


int i = 0;


for (i = 0; i < numInputs; i++) {


    txHeader[i + 5] = *inputs[i];


    txHeader[i + 6] = 4;


}


txHeader[numInputs + 7] = 4;




// Add the output transaction


unsigned char* outputs[] = {outputChange, op_returnAnchor};


unsigned int numOutputs = 2;


i = 0;


for (i = 0; i < numOutputs; i++) {


    txHeader[i + 9] = *outputs[i];


}


txHeader[numOutputs + 10] = 4;




// Sign the transaction


unsigned char signature[64];


EthereumSignature::create(txHeader, 13, &signature);




// Print out the signed transaction


printf("Signed Transaction:\n");


for (i = 0; i < 64; i++) {


    printf("%02x ", txHeader[i]);


}


printf("\n");




// Clean up


delete[] txHeader;

The Regtest Backend

As mentioned in your question, we’ll also be using our Regtest backend to test out this creation. In Regtest, you can set the chainhash field of the transaction header to manually specify which blockchain to create the transaction on.

Here’s an example of how you could use Regtest:

regtest -block 12345 -chainhash

Conclusion

In this tutorial, we’ve walked through the process of creating a manually signed Bitcoin transaction with one input and two outputs, including one for change and one OP_RETURN anchor data.