> [...] we can use 2-party ECDSA to create 2-of-2 multisignature addresses that > look the same as regular single-signature addresses. Even the old-style > p2pkh addresses starting with 1 can be CoinSwap addresses.
Probably worth considering that p2pkh, p2wpkh and p2sh are vulnerable to the (well-known) birthday attack with 2^80 operations on average if they encode a multisig policy . This is a large number but not the security margin we are used to. It is possible to reduce the feasibility of the attack by requiring 2^80 interactions instead of purely offline operations. This works by adding a commitment round for all public keys involved in the policy. Now in order to test whether a public key results in a collision, the attacker must first engage in a commitment protocol with that public key. The "Fast Secure Two-Party ECDSA Signing" protocol by Lindell  already has such a commitment round (for reasons unrelated to Bitcoin). For example, the Gotham City two-party ECDSA wallet  has this security model because it builds on the Lindell scheme and uses p2sh-p2wpkh.  https://bitcoin.stackexchange.com/questions/54841/birthday-attack-on-p2sh  https://eprint.iacr.org/2017/552.pdf  https://github.com/KZen-networks/gotham-city On 5/25/20 1:21 PM, Chris Belcher via bitcoin-dev wrote: > === Abstract === > > Imagine a future where a user Alice has bitcoins and wants to send them > with maximal privacy, so she creates a special kind of transaction. For > anyone looking at the blockchain her transaction appears completely > normal with her coins seemingly going from address A to address B. But > in reality her coins end up in address Z which is entirely unconnected > to either A or B. > > Now imagine another user, Carol, who isn't too bothered by privacy and > sends her bitcoin using a regular wallet which exists today. But because > Carol's transaction looks exactly the same as Alice's, anybody analyzing > the blockchain must now deal with the possibility that Carol's > transaction actually sent her coins to a totally unconnected address. So > Carol's privacy is improved even though she didn't change her behaviour, > and perhaps had never even heard of this software. > > In a world where advertisers, social media and other companies want to > collect all of Alice's and Carol's data, such privacy improvement would > be incredibly valuable. And also the doubt added to every transaction > would greatly boost the fungibility of bitcoin and so make it a better > form of money. > > This undetectable privacy can be developed today by implementing > CoinSwap, although by itself that isn't enough. There must be many > building blocks which together make a good system. The software could be > standalone as a kind of bitcoin mixing app, but it could also be a > library that existing wallets can implement allowing their users to send > Bitcoin transactions with much greater privacy. > > == CoinSwap == > > Like CoinJoin, CoinSwap was invented in 2013 by Greg Maxwell. Unlike > CoinJoin it is relatively complicated to implement and so far has not > been deployed. But the idea holds great promise, and fixes many of the > problems of some kinds of CoinJoins. CoinSwap is the next step for > on-chain bitcoin privacy. > > CoinSwap is a way of trading one coin for another coin in a > non-custodial way. It is closely related to the idea of an atomic swap. > Alice and Bob can trade coins with each other by first sending to a > CoinSwap address and having those coins then sent to Bob: > > Alice's Address 1 ----> CoinSwap Address 1 ----> Bob's Address 1 > > An entirely separate set of transactions gives Bob's coins to Alice in > return: > > Bob's Address 2 ----> CoinSwap Address 2 ----> Alice's Address 2 > > Where the symbol ----> is a bitcoin transaction. > > Privacy is improved because an observer of the blockchain cannot link > Alice's Address 1 to Alice's Address 2, as there is no transaction > between them. Alice's Address 2 could either be an address in Alice's > wallet, or the address of someone else she wants to transfer money to. > CoinSwap therefore breaks the transaction graph heuristic, which is the > assumption that if a transaction A -> B is seen then the ownership of > funds actually went from A to B. > > CoinSwap doesnt break any of bitcoin's assumptions or features like an > auditable supply or pruning. It can be built on today's bitcoin without > any new soft forks. > > CoinSwap can't improve privacy much on its own, so it requires other > building block to create a truly private system. > > === ECDSA-2P === > > The original CoinSwap idea uses 2-of-2 multisig. We can get a slightly > bigger anonymity set by using 2-of-3 multisigs with a fake third public > key. For a much greater anonymity set we can use 2-party ECDSA to create > 2-of-2 multisignature addresses that look the same as regular > single-signature addresses. Even the old-style p2pkh addresses > starting with 1 can be CoinSwap addresses. > > Because the transactions blend in with the rest of bitcoin, an > application based on CoinSwap would provide much more privacy than the > existing equal-output coinjoin apps (JoinMarket, Wasabi Wallet and > Samourai Wallet's Whirlpool). CoinSwaps would also be cheaper for the > same amount of privacy, as CoinJoin users usually create multiple > CoinJoins to get effective privacy, for example JoinMarket's tumbler > script does between 7-12 coinjoins (which are bigger than regular > transactions too) when run with default parameters. > > Schnorr signatures with Musig provide a much easier way to create > invisible 2-of-2 multisig, but it is not as suitable for CoinSwap. This > is because the anonymity set for ECDSA would be much greater. All > addresses today are ECDSA, and none are schnorr. We'd have to wait for > schnorr to be added to bitcoin and then wait for users to adopt it. We > see with segwit that even after nearly 3 years that segwit adoption is > only about 60%, and segwit actually has a sizeable financial incentive > for adoption via lower fees. Schnorr when used for single-sig doesn't > have such an incentive, as Schnorr single-sig costs the same size as > today's p2wpkh, so we can expect adoption to be even slower. (Of course > there is an incentive for multisig transactions, but most transactions > are single-sig). As schnorr adoption increases this CoinSwap system > could start to use it, but for a long time I suspect it will mostly be > using ECDSA for a greater anonymity set. > > === Liquidity market === > > We can create a liquidity market for CoinSwap very similar to how > JoinMarket works for CoinJoins. In our example above Alice would be a > market taker and Bob would be a market maker. The taker Alice pays a fee > to the maker Bob in return for choosing the amount of a CoinSwap and > when it happens. This allows an excellent user experience because Alice > can create CoinSwaps for any size she wants, at any time she wants. > Right now in JoinMarket there is liquidity to create CoinJoins of sizes > up to about 200 BTC, and we can expect a similar kind of thing with > CoinSwap. > > > === Multi-transaction CoinSwaps to avoid amount correlation === > > This CoinSwap is vulnerable to amount correlation: > > AliceA (15 BTC) ----> CoinSwap AddressA ----> BobA (15 BTC) > BobB (15 BTC) ----> CoinSwap AddressB ----> AliceB (15 BTC) > > Where AliceA, AliceB are addresses belonging to Alice. BobA, BobB are > addresses belonging to Bob. If an adversary starts tracking at address > AliceA they could unmix this CoinSwap easily by searching the entire > blockchain for other transactions with amounts close to 15 BTC, which > would lead them to address AliceB. We can beat this amount correlation > attack by creating multi-transaction CoinSwaps. For example: > > AliceA (15 BTC) ----> CoinSwap AddressA ----> BobA (15 BTC) > > BobB (7 BTC) ----> CoinSwap AddressB ----> AliceB (7 BTC) > BobC (5 BTC) ----> CoinSwap AddressC ----> AliceC (5 BTC) > BobD (3 BTC) ----> CoinSwap AddressD ----> AliceD (3 BTC) > > Now in the multi-transaction CoinSwap, the market taker Alice has given > 10 BTC and got back three transactions which add up to the same amount, > but nowhere on the blockchain is there an output where Alice received > exactly 15 BTC. > > === Routing CoinSwaps to avoid a single points of trust === > > In the original CoinSwap idea there are only two parties Alice and Bob, > so when they CoinSwap Bob will know exactly where the Alice's coins > went. This means Bob is a single point of failure in Alice's privacy, > and Alice must trust him not to spy on her. > > To spread out and decentralize the trust, we can create CoinSwaps where > Alice's payment is routed through many Bobs. > > AliceA ====> Bob ====> Charlie ====> Dennis ====> AliceB > > Where the symbol ====> means one CoinSwap. In this situation Alice will > be a market taker in the liquidity market, and all the other entities > (Bob, Charlie, Dennis) will be market makers. Only Alice will know the > entire route, and the makers will only know the previous and next > bitcoin addresses along the route. > > This could be made to work by Alice handling almost everything about the > CoinSwap on the other maker's behalf. The makers wouldn't have TCP > connections between each other, but only to Alice, and she would relay > CoinSwap-relevant information between them. The other makers are not > aware whether their incoming coins came from Alice herself or the > previous maker in Alice's route. > > > === Combining multi-transaction with routing === > > Routing and multi-transaction must be combined to get both benefits. If > Alice owns multiple UTXOs (of value 6 BTC, 8 BTC and 1 BTC) then this is > easy with this configuration: > > Alice > (6 BTC) (8 BTC) (1 BTC) > | | | > | | | > v v v > Bob > (5 BTC) (5 BTC) (5 BTC) > | | | > | | | > v v v > Charlie > (9 BTC) (5 BTC) (1 BTC) > | | | > | | | > v v v > Dennis > (7 BTC) (4 BTC) (4 BTC) > | | | > | | | > v v v > Alice > > Where the downward arrow symbol is a single CoinSwap hash-time-locked > contract. Each hop uses multiple transactions so no maker (Bob, Charlie, > Dennis) is able to use amount correlation to find addresses not directly > related to them, but at each hop the total value adds up to the same > amount 15 BTC. And all 3 makers must collude in order to track the > source and destination of the bitcoins. > > If Alice starts with only a single UTXO then the above configuration is > still vulnerable to amount correlation. One of the later makers (e.g. > Dennis) knows that the total coinswap amount is 15 BTC, and could search > the blockchain to find Alice's single UTXO. In such a situation Alice > must use a branching configuration: > > Alice > (15 BTC) > | > | > v > Bob > / \ > / \ > <----------- -----------> > | | > (2 BTC) (2 BTC) (2 BTC) (3 BTC) (3 BTC) (3 BTC) > | | > | | > v v > Charlie Dennis > (1 BTC) (2 BTC) (3 BTC) (5 BTC) (3 BTC) (1 BTC) > | | | | | | > | | | | | | > v v v v v v > Edward Fred > (4 BTC) (1 BTC) (1 BTC) (4 BTC) (2 BTC) (1 BTC) > | | | | | | > | | | | | | > v v v v v v > Alice Alice > > In this diagram, Alice sends 15 BTC to Bob via CoinSwap who sends 6 BTC > on to Charlie and the remaining 9 BTC to Dennis. Charlie and Dennis do a > CoinSwap with Edward and Fred who forward the coins to Alice. None of > the makers except Bob know the full 15 BTC amount and so can't search > the blockchain backwards for Alice's initial UTXO. Because of multiple > transactions Bob cannot look forward to search for the amounts he sent 6 > BTC and 9 BTC. A minimum of 3 makers in this example need to collude to > know the source and destination of the coins. > > Another configuration is branch merging, which Alice would find useful > if she has two or more UTXOs for which there must not be evidence that > they're owned by the same entity, and so they must not be spent together > in the same transaction. > > Alice Alice > (9 BTC) (6 BTC) > | | > | | > v v > Bob Charlie > (4 BTC) (3 BTC) (2 BTC) (1 BTC) (2 BTC) (3 BTC) > | | | | | | > | | | | | | > \ \ \ / / / > \ \ \ / / / > \ \ \ / / / > >------->-------\ /-------<-------< > \ / > Alice > (15 BTC) > > In this diagram Alice sends the two UTXOs (9 BTC and 6 BTC) to two > different makers, who forward it onto Alice. Because the two UTXOs have > been transferred to different makers they will likely never be co-spent. > > These complex multi-transaction routed coinswaps are only for the > highest threat models where the makers themselves are adversaries. In > practice most users would probably choose to use just one or two hops. > > > === Breaking change output and wallet fingerprinting heuristics === > > Equal-output CoinJoins easily leak change addresses (unless they are > sweeps with no change). CoinSwap doesn't have this flaw which allows us > to break some of the weaker change output heuristics. > > For example address reuse. If an output address has been reused it is > very likely to be a payment output, not a change output. In a CoinSwap > application we can break this heuristic by having makers randomly with > some probability send their change to an address they've used before. > That will make the heuristics think that the real change address is > actually the payment address, and the real payment is actually the > change, and could result in an analyzer of the blockchain grouping the > payment address inside the maker's own wallet cluster. > > Another great heuristic to break is the script type heuristic. If the > maker's input are all in p2sh-p2wpkh addresses, and their payment > address is also of type p2sh-p2wpkh, then the maker could with some > probability set the change address to a different type such as p2wpkh. > This could trick a chain analyzer in a similar way. > > === Fidelity bonds === > > Anybody can enter the CoinSwap market as a maker, so there is a danger > of sybil attacks. This is when an adversary deploys huge numbers of > maker bots. If the taker Alice chooses maker bots which are all > controlled by the same person then that person can deanonymize Alice's > transaction by tracking the coins along the route. > > A solution to this is fidelity bonds. This is a mechanism where bitcoin > value is deliberately sacrificed to make a cryptographic identity > expensive to obtain. The sacrifice is done in a way that can be proven > to a third party. One way to create a fidelity bond is to lock up > bitcoins in a time-locked address. We can code the taker bots to behave > in a way that creates market pressure for maker bot operators to publish > fidelity bonds. These fidelity bonds can be created anonymously by > anyone who owns bitcoin. > > Fidelity bonds are a genuine sacrifice which can't be faked, they can be > compared to proof-of-work which backs bitcoin mining. Then for a sybil > attacker to be successful they would have to lock up a huge value in > bitcoin for a long time. I've previously analyzed fidelity bonds for > JoinMarket, and using realistic numbers I calculate that such a > system would require about 55000 BTC (around 500 million USD at today's > price) to be locked up for 6 months in time-locked addresses. This is a > huge amount and provides strong sybil resistance. > > ==== Who goes first ==== > > Fidelity bonds also solve the "who goes first" problem in CoinSwap. > > This problem happens because either Alice or Bob must broadcast their > funding transaction first, but if the other side halts the protocol then > they can cause Alice or Bob's to waste time and miner fees as they're > forced to use the contract transactions to get their money back. This is > a DOS attack. If a malicious CoinSwapper could keep halting the protocol > they could stop an honest user from doing a CoinSwap indefinitely. > Fidelity bonds solve this by having the fidelity bond holder go second. > If the fidelity bond holder halts the protocol then their fidelity bond > can be avoid by the user in all later CoinSwaps. And the malicious > CoinSwapper could pack the orderbook with their sybils without > sacrificing a lot of value for fidelity bonds. > > As a concrete example, Alice is a taker and Bob is a maker. Bob > publishes a fidelity bond. Alice "goes first" by sending her coins into > a 2-of-2 multisig between her and Bob. When Bob sees the transaction is > confirmed he broadcasts his own transactions into another 2-of-2 > multisig. If Bob is actually malicious and halts the protocol then he > will cost Alice some time and money, but Alice will refuse to ever > CoinSwap with Bob's fidelity bond again. > > If DOS becomes a big problem even with fidelity bonds, then its possible > to have Alice request a "DOS proof" from Bob before broadcasting, which > is a set of data containing transactions, merkle proofs and signatures > which are a contract where Bob promises to broadcast his own transaction > if Alice does so first. If Alice gets DOSed then she can share this DOS > proof publicly. The proof will have enough information to convince > anyone else that the DOS really happened, and it means that nobody else > will ever CoinSwap with Bob's fidelity bond either (or at least assign > some kind of ban score to lower the probability). I doubt it will come > to this so I haven't expanded the idea much, but theres a longer writeup > in the reference. > > === Private key handover === > > The original proposal for CoinSwap involved four transactions. Two to > pay into the multisig addresses and two to pay out. We can do better > than this with private key handover. This is an observation that once > the CoinSwap preimage is revealed, Alice and Bob don't have to sign each > other's multisig spend, instead they could hand over their private key > to the other party. The other party will know both keys of the 2-of-2 > multisig and therefore have unilateral control of the coins. Although > they would still need to watch the chain and respond in case a > hash-time-locked contract transaction is broadcasted. > > As well as saving block space, it also improves privacy because the > coins could stay unspent for a long time, potentially indefinitely. > While in the original coinswap proposal an analyst of the chain would > always see a funding transaction followed closely in time by a > settlement transaction, and this could be used as a fingerprint. > > We can go even further than private key handover using a scheme called > SAS: Succinct Atomic Swap. This scheme uses adapter signatures to > create a similar outcome to CoinSwap-with-private-key-handover, but only > one party in the CoinSwap must watch and respond to blockchain events > until they spend the coin. The other party just gets unilateral control > of their coins without needing to watch and respond. > > > === PayJoin with CoinSwap === > > CoinSwap can be combined with CoinJoin. In original CoinSwap, Alice > might pay into a CoinSwap address with a regular transaction spending > multiple of her own inputs: > > AliceInputA (1 BTC) ----> CoinSwap Address (3 BTC) > AliceInputB (2 BTC) > > This leaks information that all of those inputs are owned by the same > person. We can make this example transaction a CoinJoin by involving > Bob's inputs too. CoinJoin requires interaction but because Alice and > Bob are already interacting to follow the CoinSwap protocol, so it's not > too hard to have them interact a bit more to do a CoinJoin too. The > CoinJoin transaction which funds the CoinSwap address would look like this: > > AliceInputA (1 BTC) ----> CoinSwap Address (7 BTC) > AliceInputB (2 BTC) > BobInputA (4 BTC) > > Alice's and Bob's inputs are both spent in a same transaction, which > breaks the common-input-ownership heuristic. This form of CoinJoin is > most similar to the PayJoin protocol or CoinJoinXT protocol. As with the > rest of this design, this protocol does not have any special patterns > and so is indistinguishable from any regular bitcoin transaction. > > To make this work Bob the maker needs to provide two unrelated UTXOs, > one that is CoinSwapped and the other CoinJoined. > > ==== Using decoy UTXOs to protecting from leaks ==== > > If Bob the maker was just handing out inputs for CoinJoins to any Alice > who asked, then malicious Alice's could constantly poll Bob to learn his > UTXO and then halt the protocol. Malicious Alice could learn all of > Bob's UTXOs and easily unmix future CoinSwaps by watching their future > spends. > > To defend against this attack we have Bob maintain a list of "decoy > UTXOs", which are UTXOs that Bob found by scanning recent blocks. Then > when creating the CoinJoin, Bob doesn't just send his own input but > sends perhaps 50 or 100 other inputs which don't belong to him. For the > protocol to continue Alice must partially-sign many CoinJoin > transactions; one for each of those inputs, and send them back to Bob. > Then Bob can sign the transaction which contains his genuine input and > broadcast it. If Alice is actually a malicious spy she won't learn Bob's > input for sure but will only know 100 other inputs, the majority of > which have nothing to do with Bob. By the time malicious Alice learns > Bob's true UTXO its already too late because its been spent and Alice is > locked into the CoinSwap protocol, requiring time, miner fees and > CoinSwap fees to get out. > > This method of decoy UTXOs has already been written about in the > original PayJoin designs from 2018. > > === Creating a communication network using federated message boards === > > Right now JoinMarket uses public IRC networks for communication. This is > subpar for a number of reasons, and we can do better. > > I propose that there be a small number of volunteer-operated HTTP > servers run on Tor hidden services. Their URLs are included in the > CoinSwap software by default. They can be called message board servers. > Makers are also servers run on hidden services, and to advertise > themselves they connect to these message board servers to post the > makers own .onion address. To protect from spam, makers must provide a > fidelity bond before being allowed to write to the HTTP server. > > Takers connect to all these HTTP message boards and download the list of > all known maker .onion addresses. They connect to each maker's onion to > obtain parameters like offered coinswap fee and maximum coinswap size. > This is equivalent to downloading the orderbook on JoinMarket. Once > takers have chosen which makers they'll do a CoinSwap with, they > communicate with those maker again directly through their .onion address > to transmit the data needed to create CoinSwaps. > > These HTTP message board servers can be run quite cheaply, which is > required as they'd be volunteer run. They shouldn't require much > bandwidth or disk space, as they are well-protected from spam with the > fidelity bond requirement. The system can also tolerate temporary > downtimes so the servers don't need to be too reliable either. It's easy > to imagine the volunteers running them on a raspberry pi in their own > home. These message board servers are similar in some ways to the DNS > seeds used by Bitcoin Core to find its first peers on bitcoin's p2p > network. If the volunteers ever lose interest or disappear, then the > community of users could find new volunteer operators and add those URLs > to the default list. > > In order to censor a maker, _all_ the message board servers would have > to co-operate to censor him. If censorship is happening on a large scale > (for example if the message board servers only display sybil makers run > by themselves) then takers could also notice a drop in the total value > of all fidelity bonds. > > > == How are CoinSwap and Lightning Network different? == > > CoinSwap and Lightning Network have many similarities, so it's natural > to ask why are they different, and why do we need a CoinSwap system at > all if we already have Lightning? > > === CoinSwap can be adopted unilaterally and is on-chain === > > Today we see some centralized exchange not supporting so-called > ``privacy altcoins'' because of regulatory compliance concerns. We also > see some exchanges frowning upon or blocking CoinJoin transaction they > detect. (There is some debate over whether the exchanges really > blocked transactions because they were CoinJoin, but the principle > remains that equal-output CoinJoins are inherently visible as such). > It's possible that those exchanges will never adopt Lightning because of > its privacy features. > > Such a refusal would simply not be possible with CoinSwap, because it is > fundamentally an on-chain technology. CoinSwap users pay to bitcoin > addresses, not Lightning invoices. Anybody who accepts bitcoin today > will accept CoinSwap. And because CoinSwap transactions can be made > indistinguishable from regular transactions, it would be very difficult > to even determine whether they got paid via a CoinSwap or not. So > CoinSwap is not a replacement for Lightning, instead it is a replacement > for on-chain privacy technology such as equal-output CoinJoins which are > implemented today in JoinMarket, Wasabi Wallet and Samourai Wallet. > Ideally this design, if implemented, would be possible to include into > the many already-existing bitcoin wallets, and so the CoinSwaps would be > accessible to everyone. > > This feature of CoinSwap will in turn help Lightning Network, because > those censoring exchanges won't be able to stop transactions with > undetectable privacy no matter what they do. When they realize this > they'll likely just implement Lightning Network anyway regardless of the > privacy. > > Bitcoin needs on-chain privacy as well, otherwise the bad privacy can > leak into layer-2 solutions. > > === Different ways of solving liquidity === > > Lightning Network cannot support large payment amounts. Liquidity in > payment channels on the Lightning network is a scarce resource. Nodes > which relay lightning payments always take care that a payment does not > exhaust their liquidity. Users of Lightning today must often be aware of > inbound liquidity, outbound liquidity and channel rebalancing. There > even exist services today which sell Lightning liquidity. > > This CoinSwap design solves its liquidity problem in a completely > different way. Because of the liquidity market similar to JoinMarket, > all the required liquidity is always available. There are never any > concerns about exhausting channel capacity or a route not being found, > because such liquidity is simply purchased from the liquidity market > right before it is used. > > It is still early days for Lightning, and liquidity has been a known > issue since the start. Many people are confident that the liquidity > issue will be improved. Yet it seems hard to imagine that Lightning > Network will ever reliably route payments of 200 BTC to any node in the > network (and it doesn't have to to be successful), yet on JoinMarket > today as I write these words there are offers to create CoinJoins with > amounts up to around 200 BTC. We can expect similar large amounts to be > sendable in CoinSwap. The liquidity market as a solution is known to > work and has been working for years. > > === Sybil resistance === > > CoinSwap can support fidelity bonds and so can be made much more > resistant to sybil attacks. We saw in the earlier section that realistic > numbers from JoinMarket imply a sybil attacker would have to lock up > hundreds of millions of USD worth of bitcoin to successfully deanonymize > users. > > It's difficult to compare this to the cost of a sybil attack in > Lightning network as such attacks are hard to analyze. For example, the > attacker needs to convince users to route payments through the > attacker's own nodes, and maybe they could do this, but putting numbers > on it is hard. Even so it is very likely that the true cost is much less > than 500 million USD locked up for months because Lightning nodes can be > set up for not more than the cost of hardware and payment channel > capacity, while CoinSwap makers would require expensive fidelity bond > sacrifices. > > As this CoinSwap design would cost much more sybil attack, its privacy > would be much greater in this respect. > > > == How are CoinSwap, PayJoin and PaySwap different? == > > PayJoin can also be indistinguishable from regular bitcoin transaction, > so why don't we all just that and not go further? > > The answer is the threat models. PayJoin works by having the customer > and merchant together co-operate to increase both their privacy. It > works if the adversary of both of them is a passive observer of the > blockchain. > > PayJoin doesnt help a customer at all if the user's adversary is the > merchant. This situation happens all the time today, for example > exchanges spying on their customers. CoinSwap can help in this > situation, as it doesn't assume or require that the second party is your > friend. The same argument applies to PaySwap. > > Obviously PayJoin and PaySwap are still very useful, but they operate > under different threat models. > > > == Conclusion == > > CoinSwap is a promising privacy protocol because it breaks the > transaction graph heuristic, but it cant work on its own. In order to > create a truly private system of sending transactions which would > improve bitcoin's fungibility, CoinSwap must be combined with a couple > of other building blocks: > > * ECDSA-2P > * Liquidity market > * Routed CoinSwaps > * Multi-transaction CoinSwaps > * Breaking change output heuristics > * Fidelity bonds > * PayJoin with CoinSwap > * Federated message boards protected from spam with fidelity bonds > > CoinSwap transactions could be made to look just like any other regular > bitcoin transaction, with no distinguishing fingerprint. This would make > them invisible. > > I intend to create this CoinSwap software. It will be almost completely > decentralized and available for all to use for free. The design is > published here for review. If you want to help support development I > accept donations at https://bitcoinprivacy.me/coinswap-donations > > > == References == > > -  "CoinSwap: Transaction graph disjoint trustless trading" > https://bitcointalk.org/index.php?topic=321228.0 > > -  > http://diyhpl.us/wiki/transcripts/scalingbitcoin/tokyo-2018/scriptless-ecdsa/ > > -  https://en.bitcoin.it/wiki/Privacy#Change_address_detection > > -  "Design for improving JoinMarket's resistance to sybil attacks > using fidelity bonds" > https://gist.github.com/chris-belcher/18ea0e6acdb885a2bfbdee43dcd6b5af/ > > -  https://github.com/AdamISZ/CoinSwapCS/issues/50 > > -  https://github.com/AdamISZ/CoinSwapCS/issues/53 > > -  > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-May/017846.html > > -  > https://github.com/ElementsProject/scriptless-scripts/blob/master/md/atomic-swap.md > > -  > https://blockstream.com/2018/08/08/en-improving-privacy-using-pay-to-endpoint/ > > -  https://medium.com/@nopara73/pay-to-endpoint-56eb05d3cac6 > > -  > https://cointelegraph.com/news/binance-returns-frozen-btc-after-user-promises-not-to-use-coinjoin > > > _______________________________________________ > bitcoin-dev mailing list > firstname.lastname@example.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > _______________________________________________ bitcoin-dev mailing list email@example.com https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev