New Bitcoin Cash Specs Propose Heightened Privacy and Double-Spend Proofs

Bitcoin Cash (BCH) development continues as software engineers have revealed two distinct concepts that aim to boost the BCH network. Bitcoin Cash developer Tom Zander has announced new documentation concerning the vision of double-spend proofs, which now exists as a pull request to the alternative BCH implementation Flowee the Hub. Additionally, Electron Cash developer Jonald Fyookball has reported on the expanded specifications for the Cashshuffle method Cashfusion, a scheme that adds higher levels of privacy to unlinkable coins.

Also Read: Exploring the SLP Token Universe Built on the Bitcoin Cash Chain

Cashfusion Specifications Enhanced

Developers put a lot of time and effort into creating applications and platforms that make bitcoin cash easier to use, more secure, and sometimes more private. On Monday, Electron Cash and Cashshuffle developer Jonald Fyookball informed the BCH community that “Cashfusion got a whole lot better.” Cashfusion is an extension of Cashshuffle, the BCH shuffling application that doesn’t require a trusted third party. The application offers a superior anonymity set by obfuscating the relationship between the owner’s old and new BCH addresses within the shuffling process. To many BCH proponents, Cashshuffle is very good but the spectrum of privacy can be improved. For instance, if a user has mixed a bunch of coins and they eventually consolidate them into one address it can still leave behind some clues for blockchain analysis.

“We need a method to coordinate Coinjoin transactions with multiple inputs per user,” explains the Cashfusion specifications. “This is inherently challenging because we want to hide input linkages while simultaneously attempting to blame/ban users who don’t sign all their inputs.” However, Cashfusion proposes a blind verification scheme where each input and output is verified by a random Cashshuffle participant while also providing a series of cryptographic commitments than can identify and ban uncooperative participants. The Cashfusion author’s add:

CashFusion provides high levels of privacy via a flexible scheme that allows an arbitrary number of inputs and outputs of non-standard amounts. It provides anonymous, trustless coordination with usually zero-knowledge of linkages revealed to other players or the server.

Fyookball explained he’s been working with independent software developer Mark Lundeberg and has put “100+ revisions” into the project since he last updated the community. “The new scheme not only is more secure, but allows basically any number of inputs and outputs of any amounts — This means it can offer high levels of privacy with unlinkable coins,” Fyookball asserted. Cashshuffle has been an extremely popular application for BCH and so far, according to data stemming from Acidsploit’s Cashshuffle stats page, there’s been 116,438 BCH or more than $34 million at today’s BCH prices shuffled to date. There’s been a total of 21,336 shuffles mixing all those coins since March 27. Moreover, thanks to the release of the Cashshuffle JS library, other wallets like Bitcoin.com’s noncustodial wallet will provide Cashshuffle features as well.

Double-Spend Proofs

On the same day, the software developer Tom Zander revealed the completion of a pull request to the alternative BCH implementation Flowee the Hub which aims to provide double-spend proofs (DSP). Essentially the concept of DSP documentation is authored by the developer Imaginary Username and the idea adds a fraud-proof system for double-spending. DSP was also adapted from Chris Pacia’s Double Spend Alert work and Mark Lundeberg has been contributing to the project. Zander said on Monday that the system they came up with is a “relatively small (constant size) message with actual proof that the spender signed two different transactions spending the money you were hoping to receive.” The software engineer added that the important aspect of DSP is to make sure an original double-spending transaction cannot be recreated. “Double spend proofs have been an idea for years, with lots of people talking about it and we had some initial specs and even a conference about this last year,” Zander told the BCH community.

“This document describes a new Bitcoin Cash network message that is generated when two transactions spending the same input are detected on a participating node, and related protocol to relay it through the network among participating nodes,” the specification explains on Github. “A transaction that has its inputs all being from P2PKH or P2SH-multisig outputs, follow prevailing standardness rules and has all signatures signed with SIGHASH_ALL without the ANYONECANPAY flag,” the developer’s data notes. And in the case of P2SH-multisig containing all unique pubkeys, is hereby referred to as ‘protected transactions.’”

Striving to Capture Two Crypto Holy Grails

Bitcoin Cash proponents were pleased to hear both announcements on July 29, as each could reinforce private transactions and zero-confirmation acceptance. For some people, along with scaling BCH to serve the needs of millions, a deeper form of transaction confidentiality and double-spend proofs are holy grails of sorts. Zander also compared the new pull request to the double-spend relaying/detection plan that stemmed from Bitcoin XT and was later merged into Bitcoin Unlimited. The Flowee developer said one contrast is that double-spend relays propagate the whole transaction (txn) without any annotation, basically dropping the biggest protection of ‘first seen safe.’ The programmer also stated that SPV nodes (light clients) that were once safe from seeing a txn now see them and in known cases “relaying makes double-spending an SPV wallet actually trivial.” “The main reason why double spends can propagate is because of different settings between nodes. Double spend relay makes this use case also worse whereas a proof solves this use case,” Zander emphasized.

With Cashfusion, BCH supporters are excited because the protocol could help make a good majority of BCH transactions fungible and private if large numbers of people mix coins. One BCH fan wrote: “Great news — I’ve been supported the pool but waiting for something like this before recommending it to muggles. The status quo is too much to have to keep in mind for widely-deployed opsec — Thanks for everybody’s work on this.” Improved privacy couldn’t come at a better time as the regulatory climate surrounding digital assets has increased significantly in recent months. Just recently the U.S. tax agency (IRS) notified the public that 10,000 Americans would receive letters reminding them to file taxes. Crypto fans believe that companies pressured to fork over data due to grand subpoenas and exchanges that use blockchain surveillance are a threat to digital currency privacy. Cashshuffle coupled with Cashfusion could improve anonymity sets by avoiding amount linkages found using combinatorics and man-in-the-middle (MITM) attacks.

“We wish to prove that zero-knowledge (beyond what is publicly available) is revealed about any of the players’ inputs or outputs during the fusion process — It works because the linkages between players’ commitments are only kept by the server, and the server doesn’t participate in verification,” the Cashfusion documentation concludes.

What do you think about the double-spend proofs and Cashfusion specs? Let us know what you think about these concepts in the comments section below.

Image credits: Shutterstock, Github, Twitter, and Pixabay.

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