Private Tx

Javascript chain analysis library for node.js and browsers written in TypeScript, designed to help developers, researchers, and analysis tools to examine the inputs and outputs of Bitcoin transactions and identify potential privacy leaks.

Given a transaction it provides heuristics information on:

• Address Reuse: identifies instances where input addresses are being reused as outputs addresses.
• Common Inputs: detect if inputs in a transaction are likely to come from the same wallet.
• Change Outputs Detection: provides indices of all change outputs in a transaction.
• Peeled Transaction: determine if a transaction is peeled and provide the payment output index and the change output index.
• Detect lightning channel closing input given a transaction returns all inputs that are likely to be a lightning channel closing transaction input

Usage

The library is built to improve privacy for Bitcoin users by providing a tool for identifying potential privacy leaks. It can be used by developers building more privacy-preserving applications or by researchers analyzing the privacy properties of the Bitcoin network. With its comprehensive analysis capabilities, PrivateTx offers a valuable tool for anyone looking to better understand the privacy implications of Bitcoin transactions

To ensure privacy and avoid detection by chain analysis tools, it is essential to test constructed transactions against the most common heuristics used by these tools to cluster transactions and determine wallet balances. Running the constructed transaction against these heuristics, one at a time, and verifying that it passes without analysis is crucial to ensure the wallet's resistance to chain analysis. This process helps to ensure the privacy of the transaction and the security of the wallet.

Installation Guide

$ npm install privatetx-lib

Examples

Transaction input format

Processed Base 64 PSBT

1. Address Reuse

import { checkAddressReuse } from "privatetx-lib";

const transactionPsbt = "cHNidP8BAHUCAAAAASaBcTce3/KF6Tet7qSze3gADA.....";

const reusedAddresses = checkAddressReuse(transactionPsbt);

console.log(reusedAddresses);
// { status: true, data: [ { vin:0, vout: 1} ] }

This example demonstrates address reuse in a transaction, where the address of the first input is reused as the second output address.

The output of this function includes:

• The status Boolean, where true indicates the presence of address reuse and false indicates the absence of address reuse.
• An array of objects contained in data, representing instances of address reuse. Each object in the array contains the input index vin and output index vout where the address was reused.

2. Common Inputs

import { commonInputs } from "privatetx-lib";

const transactionPsbt = "cHNidP8BAO4CAAAAA7.....";

const inputsCommon = commonInputs(transactionPsbt);

console.log(inputsCommon);
// true

In the above example, the commonInputs function is used to check if the inputs of a given transaction are common and likely to come from the same wallet. If the inputs are common, the output will be true, and if they are not, the output will be false.

3. Detect Change Outputs

import { detectChange } from "privatetx-lib";

const transactionPsbt = "cHNidP8BAO4CAAAAA7.....";

const changeOutputs = detectChange(transactionPsbt);

console.log(changeOutputs);
// { status: true, changeOutputIndices: [ 0 ], heuristic: 'Different output script type' }

The output of the function is an object with three properties:

• status: a boolean that indicates whether change outputs were detected (true) or not (false).
• changeOutputIndices: an array of integers representing the indices of the detected change outputs.
• heuristic: a string that provides information on the heuristic used to detect the change outputs. In this example, the heuristic used is "Different output script type". The heuristics used by this functions are Address reuse, Different output script type , Output greater than all inputs, Non-round number outputs , Largest output

In this particular example, the output indicates that change outputs were detected (status: true) and that the only detected change output is at index 0 (changeOutputIndices: [ 0 ]). The heuristic used to detect the change outputs was "Different output script type".

4. Peeling Transaction

import { peelingTransaction } from "privatetx-lib";

const transactionPsbt = "cHNidP8BAO4CAAAAA7Qi7ef.....";

const transactionIsPeeled = peelingTransaction(transactionPsbt);

console.log(transactionIsPeeled);
// { status: true, index: 2 }

The output of this function is an object with a status property that is true if the transaction specified in transactionPsbt is peeled, and false otherwise. Additionally, if the transaction is peeled, the object will contain an index property that indicates the index of the change output, where as all other outputs in the transaction are payments.

The example output is an object with a status property that is true, which means the transaction is peeled, and the change output index that is 2 (which means the the third output).

5. Detect Lightning channel close inputs

Transaction input format

Base 64 PSBT or a raw Transaction hex

import { detectLightningChannelClosePsbt, detectLightningChannelClose  } from "privatetx-lib";

const transactionPsbt = "cHNidP8BAO4CAAAAA7Qi7ef.....";

const transactionHex = "01000000000101489de8818d4588ca7b11df95eadf3bbd6612df9e31c0e793d2f853a9626fbdc60300000000fffffff";

const closingChannelInputs = detectLightningChannelClosePsbt(transactionPsbt);

const closingChannelInputsTransactionHex = detectLightningChannelClose(transactionPsbt)

console.log(closingChannelInputs);
// { status: true, inputs: [ 0 ] }

console.log(closingChannelInputsTransactionHex);
// { status: true, inputs: [ 0 ] }

The output of this function is an object with a status property that is true if the specified transaction has Lightning channel closing inputs and false otherwise. Additionally, the inputs key will contain an array of the indexes of the inputs that are Lightning closing inputs, where all other inputs are not Lightning closing inputs.

In the example output above, the status property is true, which indicates that the transaction has at least one Lightning channel closing input, and the first input is a Lightning channel closing input.

Tests

$ npm run test

Test folder

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This project is built during Qala bitcoin development training cohort, a program training African software engineers transitioning to bitcoin and open source software development.

Stay in touch

Twitter

• Abubakar Sadiq Ismail
• Qala

License

MIT licensed.

Feel free to create a PR for an improvement or open an issue if you encounter one.

Dont Trust, Verify!!!

Happy Hacking ❤️