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Introduction

In the ever-evolving world of bitcoin, privacy and security are a paramount standard. CoinJoin, a method for enhancing anonymity in Bitcoin transactions, largely depends on how it will be implemented, as it offers a unique approach. In this blog post, we'll delve into the best practices for using encrypted channels in each CoinJoin round within JoinStr, ensuring that your transactions are not just anonymous but also secure.

Understanding CoinJoin and JoinStr

Before diving into the specifics, it's crucial to understand what CoinJoin is and how JoinStr fits into the picture. CoinJoin is a mechanism that combines multiple Bitcoin payments from several users into a single transaction, making it more difficult for outsiders to determine who paid whom. JoinStr indeed, is a coinjoin implemetation written in Python that utilizes nostr relays for the transaction coordination, adding an extra layer of security. To achieve this implementation, the implementation of private channels is mandatory and we are currentluy working on it to make it real.
We recently submitted a 0.0135 BTC bounty to incentivize the community to participate and submit proposals, hopefully it will be published soon on https://bountsr.org/joinstr-channels/ To explain how to implement private channels into Joinstr, we also need to understand a few key concepts:
  1. CoinJoin Mechanism: is a method for combining multiple Bitcoin payments from multiple spenders into a single transaction to increase privacy. It obscures the link between the input and output of a transaction, making it more difficult to trace individual transactions. Learn more about Coinjoin since its inception!
  2. Joinstr's Implementation: uses nostr relays for coordination. Nostr (Notes and Other Stuff Transmitted by Relays) is a decentralized and censorship-resistant protocol. It's used in Joinstr to coordinate transactions between different parties. There's also plenty of info about the protocol on Nostr.how, check it out!
  3. Private Channels Concept: in the context of bitcoin on-chain, it refers to a method of conducting transactions or communications in a private, secure manner, often using encryption or other encryption techniques. You can learn more about it on here and here :)

The Role of Encrypted Channels

Encrypted channels in JoinStr play a vital role. They ensure that the details of the transaction, and the participants involved, remain confidential. This encryption is vital in protecting against potential threats, such as man-in-the-middle attacks or blockchain analysis techniques that could compromise privacy. This will enable Joinstr to solve its Denial of Service, an issue initially discussed on the bitcoin-dev mailing list. After drafting a NIP to try solve this problem we realized that using encrypted channels would be a muuuch better approach. There are some exisiting NIPs for encrypted channels that could be useful: NIP 38, NIP 48 and NIP 112, although some changes would be required to implement them on joinstr.

Best Practices for Using Encrypted Channels in JoinStr

1. Choose Strong Encryption: Always opt for the strongest encryption settings available in JoinStr. This might mean taking a bit more time to set up your transaction, but the added security it's definitely worth for your anonymity.
2. Verify Your Counterparties: While JoinStr does a lot to secure transactions, it's still important to verify whom you're transacting with (when possible). This doesn't mean you need to know their identity, but ensure they are legitimate participants in the CoinJoin.
3. Use Fresh Addresses: Each time you participate in a CoinJoin round, use a new address. This practice prevents linking your transactions together, enhancing privacy.
4. Stay Updated: Keep your JoinStr software up to date. Our comunity continuously work on improving security features and fixing vulnerabilities. Using the latest version ensures you have the best protection available.
5. Monitor CoinJoin Rounds: Pay attention to the details of each CoinJoin round. If something seems off, such as a participant repeatedly trying to join with the same inputs, it might be a red flag.
6. Avoid Reusing Channels: Just as with addresses, try not to reuse encrypted channels. New channels for each round minimize the risk of pattern recognition.
7. Be Cautious with Amounts: When participating in CoinJoin, consider the amounts you're mixing. Large, unique amounts can sometimes be traced back. Aim for common denominations where possible.
8. Understand the Limits: Remember that while CoinJoin and encrypted channels add privacy, they are not foolproof. Understanding their limitations helps in making informed decisions about your transactions.

Ideal integration

One user will create an encrypted channel, post output address in the channel and share info to join the channel as a public event. Other users will join the channel and register their outputs. Once the encrypted channel is full based on capacity defined by the first user, nobody should be able to join the channel.
Input registration would also use the same channel, followed by the coinjoin finalization and confirmation in the blockchain.
To integrate private channels into Joinstr, you would need to follow these general steps:
  1. Understand Nostr Protocol: Since Joinstr uses nostr for coordination, a deep understanding of how nostr works is crucial. This includes how it handles data transmission and ensures privacy and security using the NIPs: 38, 48 and 112.
  2. Design the Private Channel: Determine how the private channel will function within the Joinstr framework. This involves deciding on the encryption methods, how the channel will be established, and how it will interact with the existing nostr relay system.
  3. Implement Encryption: Implement robust encryption methods for the private channel. This is essential to ensure that the details of the transactions coordinated through Joinstr are kept confidential.
  4. Modify Joinstr's Code: Integrate the private channel functionality into Joinstr's existing Python codebase. This will involve coding the mechanisms for establishing and maintaining private channels and ensuring they work seamlessly with the nostr relay system.
  5. Testing and Validation: Rigorously test the implementation to ensure that it not only maintains privacy but also works efficiently and securely within the Joinstr framework.
  6. Document the process and seek Community Feedback: Update the Joinstr documentation to include information about the new private channel feature. Engage with the Joinstr and broader cryptocurrency community for feedback and improvements.

Conclusion

Using encrypted channels in each CoinJoin round within JoinStr is a powerful way to enhance your transaction privacy, anonymity and security. By following these best practices, you can ensure that you're making the most out of this innovative technology.
We invite all the participants to help us build this functionality applying to the bounty and ideally writing a public article to share and validate the process adopted. Remember to check Joinstr documentation and share your thoughts and questions on our public Telegram channel.
Looking forward to hearing from you all! Cheers 🤙