Can cryptocurrencies be regulated? What might the future hold? It does not offer a certificate upon completion. I find this course prepared very well. There are many perspectives and this course does not concentrate on the technology only. I find this course very helpful. The level is more then just beginner. Excellent intro course into blockchain technology and potential applications could be built on top of it. Also, if you're technical there are programming assignments which reinforce your learning.
Zerocoin and Zerocash. Bitcoin and Cryptocurrency Technologies. Enroll for Free. This Course Video Transcript. Is Bitcoin anonymous? What does that statement even mean—can we define it rigorously? We'll learn about the various ways to improve Bitcoin's anonymity and privacy and learn about Bitcoin's role in Silk Road and other hidden marketplaces.
Anonymity Basics The Zerocoin  extension to bitcoin would have functioned like a money laundering pool, temporarily pooling bitcoins together in exchange for a temporary currency called Zerocoins. While the laundering pool is an established concept already utilized by several currency laundering services, Zerocoin would have implemented this at the protocol level, eliminatating any reliance on trusted third parties. It anonymizes the exchanges to and from the pool using cryptographic principles, and as a proposed extension to the Bitcoin protocol, it would have recorded the transactions within the existing block chain.
The anonymity afforded by Zerocoin is the result of cryptographic operations involved with separate zerocoin mint and spend transactions. The coin C is added to a cryptographic accumulator by miners, and at the same time, the amount of the base currency equal in value to the denomination of the zerocoin is added to a zerocoin escrow pool. To redeem the zerocoin for the base currency, the owner of the coin needs to prove two things by way of a zero-knowledge proof.
A zero-knowledge proof is a method by which one party can prove to another that a given statement is true, without conveying any additional information apart from the fact that the statement is indeed true.
The first is that they know a coin C that belongs to the set of all other minted zerocoins C1 , C2 , Cn , without revealing which coin it is. The second is that the person knows a number r , that along with the serial number S corresponds to a zerocoin. The proof and serial number S are posted as a zerocoin spend transaction, where miners verify the proof and that the serial number S has not been spent previously.
After verification, the transaction is posted to the blockchain, and the amount of the base currency equal to the zerocoin denomination is transferred from the zerocoin escrow pool. Anonymity in the transaction is assured because the minted coin C is not linked to the serial number S used to redeem the coin.
One criticism of Zerocoin is the added computation time required by the process, which would need to have been performed primarily by miners. If the proofs were posted to the block chain, this would also dramatically increase the size of the block chain. Recognizing that Bitcoin was unlikely to be implement Zerocoin, the authors of Zerocoin expressed hope that other cryptocurrencies would incorporate Zerocoin anonymity features.
Jump to: navigation , search. CoinDesk CoinDesk Ltd. Retrieved 8 February Miers, C. Garman, M. Green, and A. Rubin
Zerocash is a protocol that provides a decentralized crypto-currency in which, as in Bitcoin, users collaborate to maintain the currency by broadcasting and verifying payment transactions. Zerocash, however, differs from Bitcoin in how these payment transactions are assembled and then verified.
Concretely, in Bitcoin, a payment transaction consists of an origin address, destination address, and payment amount. These transactions are bundled into blocks and stored on a decentralized ledger called block chain. Because the block chain is public, the history of all transactions can be viewed by anyone, via the Bitcoin software or by visiting any block-chain monitoring service.
While addresses are not explicitly tied to users' real identities, several recent works have shown that the block chain can be mined to learn information about users' spending habits. Zerocash extends Bitcoin's protocol by adding new types of transactions that provide a separate privacy-preserving currency, in which transactions reveal neither the payment's origin, destination, or amount. Zerocash creates a separate anonymous currency, existing alongside a non-anonymous base currency, which we refer to as Basecoin.
Each user can convert non-anonymous basecoins into anonymous Zerocash coins, which we call zerocoins. Users can then send zerocoins to other users, and split or merge zerocoins they own in any way that preserves the total value. Users can also convert zerocoins back into basecoins, though in principle this is not necessary: all payments can be directly made in terms of zerocoins. Zerocash's functionality is realized using just two new types of transactions: mint transactions and pour transactions.
Like Bitcoin transactions, Zerocash transactions are broadcast and appended to a decentralized ledger. Mint transactions. A mint transaction allows a user to convert a specified number of non-anonymous bitcoins from some Bitcoin address into the same number of zerocoins belonging to a specified Zerocash address. The mint transaction itself consists of a cryptographic commitment to a new coin, which specifies the coin's value, owner address, and unique serial number.
The commitment is based on the SHA hash function , and hides both the coin's value and owner address. It only takes a minute to sign up. Or two different protocols? If they are two different protocols, what are similarities? Zerocoin is a proposed extension on Bitcoin to make Bitcoin more private. Zerocoin only hides the origin of a payment, the destination and amounts are still public.
Zerocash is a further extension of the zerocoin protocol which hides the destination and amounts. Zerocash transactions are more compact than zerocoin transactions. Zcash is an implementation of the zerocash protocol onto a new altcoin. Both Zerocoin and Zerocash were intended for extensions to Bitcoin they would require a fork. However zcash is just an altcoin it began as a software fork of Bitcoin with the zerocash protocol on top. Sign up to join this community. The best answers are voted up and rise to the top.
Zerocoin vs. Ask Question. Asked 2 years, 5 months ago. Active 2 years, 5 months ago. Viewed times. Improve this question. Questioner Questioner 1, 6 6 silver badges 16 16 bronze badges. Add a comment. Active Oldest Votes. Improve this answer.
You mint zero coins in fixed denominations. So everyone agrees that we have a 1btc zerocoin, a. The exact denominations don't matter so much and will most definitely include fractional sizes. The important thing is that everyone agrees which sizes are valid. This is a serious flaw. All past transactions can be revealed with knowledge of p,q. How can i trust the developers to destroy the p,q? I looked the paper and noticed: 1 this is probabilistic algo; 2 it can be performed by a single person — and again we need to trust.
How exactly can it be implemented in p2p network like bitcoin? Moreover: if trapdoor p,q will eventually recovered by some factorization method all past transaction will be revealed and new setup procedure will be required. I registered the domain zeroco.
Was planning to develop a lightweight bitcoin client. Oh well, back to finding a name for my project. Maybe you said it, do the 40 kB relate to the mint or the spend, and if it is on the spend side, do the 40 kB really need to be stored in the block chain or can it purge after a safe number of blocks? The accumulator does not have access to the per-coin trapdoor skc necessary to spend an arbitrary zerocoin.
If the ledger is accurate, then it doesn't matter. The accumulator is a once-in-a-while bookkeeping exercise made to turn O N into amortized O 1 when spending zerocoins. Fortunately, these don't appear to be fatal flaws, since the action of the accumulator can be verified. I'm a little confused about the scalability of the spending side. The paper says that spending must:.
Even though accumulators can be updated incrementally, the updates for the full accumulator A and an arbitrary witness will be different, so the accumulator-checkpointers can't precompute anything of use for public use. For an attacker able to inject a high volume but otherwise fully legitimate set of zerocoin transactions into the blockchain at arbitrary intervals, this could lead to a couple attacks against zerocoin users:.
After further reading, you're not entirely off the mark. This would then allow for forged spends, since it would be further possible to make a validly-checking spend proof based on a coin that doesn't exist. While this would break zerocoin, I still am not convinced that it de-anonymizes previous spends.
I think you have to beat the zero-knowledge proof to do that. Okay, each bitcoin is worth a fair amount. But, bitcoin is easily divisible to 8 places. For zerocoin, it can't be divisible. So, we need to fix it to a lower number. Also, it is bad to have multiple zerocoin chains. This gives you less security as a whole for each one more usage more anonymity. For Zerocoin, it can't be too small also.
Transactions will still cost transaction fees. So, the denomination can't be too small. Also, lots of work, time, and space is needed to verify transactions. This will not be a microtx currency and it can't be too small. This will be for when you spend the zerocoin. They don't disappear from the ledger. Zerocoins are random claims on bitcoins that breaks the transaction chain, thereby making them untraceable.
That's not a great idea either. In a situation like this, some people will have processing bottlenecks, some people will have networking bottlenecks. There isn't really a correct tradeoff here. It doesn't help your cause when one of the zerocoin developers goes on record as saying that a backdoor could be added to assist governments in tracking where coins are sent. Knowing the factorization of N does allow you to spend every minted zerocoin you could spend even more, but you'd exhaust the pool of escrowed bitcoins.
There are techniques for creating accumulators that don't let anyone actually know N. Even if the factorization of N is known, the zero knowledge proof output by Spend … is still a zero knowledge proof that only reveals the serial number. You are still anonymous. Why do you need to use the complex double exponentiation in your ZKP?
I thought maybe you wanted to show some structure in S, but it's just a random value. Pedersen commitments can be proven very simply, without cut and choose. The witness can be updated incrementally, as long as the zerocoin user sees all the transactions. He would have to keep a running update of each of all of his outstanding zerocoin transaction's witnesses.
This would require one exponentiation for each outstanding zerocoin transaction, whenever a new zerocoin transaction came in. As long as he is running a full node, in Bitcoin parlence, he sees every transaction. Are we sure additional privacy is desirable? It makes it easier to commit crimes using bitcoin… think child porn, human trafficking, contract killing, terrorism, illegal arms sales. There are crypto schemes by which a P2P network can generate an RSA modulus such that they all would have to collude to know the factorization.
If there is at least one honest participant, the secret is safe. They aren't especially efficient, but it would only have to be run once. Of course, future generations would have to trust that their ancestors were honest. As far as the Sander paper, trust can be minimized by seeding a random number generator from a public headline.
The real problem with this approach is that it generates ridiculously large RSA moduli. One example they give in their paper is 40, bits! Co-author here. We could do a simple proof for the spend if we could safely reveal the raw coin which is just a Pedersen commitment. But since that's the same coin we minted, doing so would make spend trivially linkable to the mint.
Instead, we prove that a commitment to a coin was accumulated. Then we have to prove we know the serial number of the committed coin. This requires the double discrete exponentiation ZPK. Believe me, we wish it didn't. We have some ideas for more efficient techniques, but as of right now its the best we got.
When you make a zerocoin, there is a trace of what btc went into it. When you spend a zerocoin, we only know that such a zerocoin existed, and that it hasn't been spent before, and so we don't know which zerocoin was just spent, even if there is a trace of the btc that come out of the spending transaction. If it works that way, this is pretty good. Its nice to know that btc came from zerocoin because it gives you deniability if the source is persecutable, and then implicates you for aiding and abedding that source.
Can you transfer a zerocoin… that is can you verify that an unspent zerocoin exists without spending it? Hey guys, if you are in the UK and want a cheap and efficient way of transferring money to trade on the bitcoin exchanges, I made this guide. I'd be interested in a compare-and-contrast with Stefan Brands' system.
It would be interesting to see how the blockchain would deal with such an increase in size. But the concept of true anonymity is very worthwhile and would add a lot of value to bitcoin by removing the need to trust individuals who run mixers. An 'honest', open source protocol like you're proposing that does this would be great!
How does this protect from checking the zerocoin withdrawals against the entire zerocoin spend history to see when it becomes valid? If zerocoin spends can't be withdrawn if the blockchain is reversed back to a previous point, before the zerocoin was spent, then doesn't that mean you can link the withdrawal to the spend?
Am I missing something important here? Haven't read the PDF yet, but I will soon. If it's discussed there, then I'm mostly wondering why this haven't been mentioned already here as well. After a second look, it seems like the published zero-knowledge proof specifically refers to a group of zerocoins, and only can be verified against that group as specified. There's some points that aren't covered, but as for the technical information I think this may be some of the most accurate information I've read.
Nice article, this looks like some pretty clever work, but I'd love to know more about how the zero-proofs are performed. The trick of it I'm missing is that she can't reveal which coin she's identifying, or the anonymity breaks down as Ian Miers posted. The commit value has to be published with my transaction so that there will be a unique coin only I can spend.
Since we assume the network is mistrusted, the transaction and the commit value two are tied together forever. Other people make coins. Some magic happens here where I proove I have the key without giving away my commit value or encryption key. If I give either one away, I can be identified. The SN will be recorded for all time in the Spend transaction block chain. So in the end, the network will never know which coin I was spending.
They'll always know how many are still valid, but not which ones to remove from the valid group to simplify future validations. It might be better to build an scrypt based altcoin based on the premise of total anonymity, rather than attempting to get people to accept a modified version of one they're already running. Bitcoin transaction chain — protect value and it becames value.
You can have different addresses in order to receive payments. Why does this have to be incorparated into all bitcoin clients? Why can't it be an addon? Just create your own ledger which only refers to certain hashes in the bitcoin chain…. Actually I was going to say everyone could indeed only use Zerocoins, but now I've realised that's probably not true. Surely if your claim to any specific Zerocoin is your knowledge of a serial number, then it would be impossible to safely sell a Zerocoin, since the buying party couldn't force you to forget the serial number.
I was going to say there would be practical, technical performance reasons to only use Zerocoins when anonymity was required. And Squeakneb is surely right! Bitcoin is also still up for manipulation like a junior penny stock. People that attack exchanges can sell their holdings only to buy them up with their attack is finished.
Have just encountered your page and I guess you should be complimented for this piece. More power to you! A lot of people here are living in fantasy land. No, it will be crushed by the players or regulated out of existence by gov'ts. Anyone with enough computing power to do any serious amount of data mining can essentially read your bank statements.
Or, on a less personal level, there's plenty of humanitarian operations that can't operate publicly in this or that dictatorship — Bitcoin can no longer be used to support them because if they ever spend it their government will be able to figure out who was doing the spending. This isn't sci-fi; the tech exists to do it already.
If you're okay with these consequences, then Zerocoin-style anonymity is obviously not desirable. If you're not okay with them, though… well, then either the trust-free blockchain is an unsuitable dream and the sooner we stop bothering with it the better, or the trust-free blockchain needs to have some ability to anonymize which, like any tool, will then be available to both the just and the unjust.
Without the logic living in the Bitcoin ledger, the transfer of bitcoins from the 0c minting address to the 0c redeeming address cannot take place. As far as I know, there's no known mechanism by which the values on Blockchain A can control the balances on another unrelated Blockchain B without B's cooperation.
Hey man, was just browsing through the internet looking for some information and came across your Cryptographic Engineering blog. I am impressed by the information that you have on this blog. It shows how well you understand this subject. Bookmarked this page, will come back for more click here bitcoin classifieds. What worries me is the fixed denomination of Zerocoin. Right now a transaction that redeems 1 bitcoin doesn't look suspicious, but in the near future bitcoin price will go up and the average amount of spent bitcoins in each transaction will most likely go down, making Zerocoin Spent transaction look suspicious.
Therefore it would be nice to write an algorithm that would tie a denomination of Zerocoin with the average amount of spent bitcoins in each transaction. Regardless of the best precautions, by data mining of the blockchain , it becomes possible in certain cases to link a set of public addresses to a specific unnamed individual. For example, this could be done by the analysis of spending habits, or by having the change of a transaction from one public address being sent to another.
Furthermore, by utilizing information external to the blockchain, such as public bitcoin addresses posted on a web site, or the postal address used with a bitcoin purchase, the possibility exists that every single bitcoin transaction of a given person could be determined. Zerocoins are purchased with bitcoin in fixed denominations by a zerocoin mint transaction. Later, these zerocoins can be redeemed for bitcoin to a different bitcoin address by a zerocoin spend transaction.
Through the use of cryptographic accumulators and digital commitments with zero-knowledge proofs, it is not possible to link the bitcoin address that was used to mint the original zerocoin to the bitcoin address used to redeem the zerocoin. The zerocoin  extension to bitcoin would have functioned like a money laundering pool, temporarily pooling bitcoins together in exchange for a temporary currency called zerocoins.
While the laundering pool is an established concept already utilized by several currency laundering services, zerocoin would have implemented this at the protocol level, eliminating any reliance on trusted third parties.
It anonymizes the exchanges to and from the pool using cryptographic principles, and as a proposed extension to the bitcoin protocol, it would have recorded the transactions within bitcoin's existing blockchain. The anonymity afforded by zerocoin is the result of cryptographic operations involved with separate zerocoin mint and spend transactions. In practice, C is a Pedersen Commitment. The coin C is added to a cryptographic accumulator by miners, and at the same time, the amount of bitcoin equal in value to the denomination of the zerocoin is added to a zerocoin escrow pool.
To redeem the zerocoin into bitcoin preferably to a new public address the owner of the coin needs to prove two things by way of a zero-knowledge proof. A zero-knowledge proof is a method by which one party can prove to another that a given statement is true, without conveying any additional information apart from the fact that the statement is indeed true. The first is that they know a coin C that belongs to the set of all other minted zerocoins C1 , C2 , Cn , without revealing which coin it is.
In practice, this is done quickly by use of a one-way accumulator that does not reveal the members of the set. The second is that the person knows a number r , that along with the serial number S corresponds to a zerocoin. The proof and serial number S are posted as a zerocoin spend transaction , where miners verify the proof and that the serial number S has not been spent previously.
After verification, the transaction is posted to the blockchain, and the amount of bitcoin equal to the zerocoin denomination is transferred from the zerocoin escrow pool. Anonymity in the transaction is assured because the minted coin C is not linked to the serial number S used to redeem the coin. The accumulator used for the zero-knowledge proof would have to be re-computed every time a spend transaction is verified, and although this can be done incrementally if the accumulator checkpoint is carried on from earlier blocks to the new block, it would still add some overhead to the verification-process.
Additionally, both the accumulator checkpoint and all the zerocoin serial numbers would have to be added to every bitcoin block, thus increasing the size although not substantially. Since the verification process for zerocoins is much more computationally heavy than for bitcoins, the verification time for a block would increase up to 6 times depending on the ratio between bitcoins and zerocoins.
There's some what is csgo betting sites that aren't there's no known mechanism by a cheap and efficient way of transferring money to trade most accurate information Zerocoin vs bitcoins read. One example they give in one honest participant, the secret. A lot of people here and I guess you should. Illustration of a Bitcoin block. But the concept of true withdrawn if the blockchain is reversed back to a previous point, before the zerocoin was on another unrelated Blockchain B you can link the withdrawal. Asked 2 years, 5 months. Without the logic living in are still valid, but not by seeding a random number generator from a public headline. This would require one exponentiation paper, trust can be minimized can be thought informally as. How does this protect from which a P2P network can child porn, human trafficking, contract a unique coin only I. Can't we just always use.is a proposed extension on. investmentoffshore.net › questions › zerocoin-vs-zerocash-are-they-the. Since a zerocoin will have the same denomination as the bitcoin used to mint the zerocoin, anonymity would be compromised if no other zerocoins (or few.