The Security Behind the Birth of Zcash | Hacker News Reader

The Security Behind the Birth of Zcash

spectrum.ieee.org

61 pointsmrb27 comments

Obligatory link to Peter Todd's experience of participating in this ceremony (for lack of a better word) — as a skeptic, no less — which is an excellent read for the opsec alone: https://petertodd.org/2016/cypherpunk-desert-bus-zcash-trust...

Thanks for sharing, really fascinating :).

The developers don't need to steal. They're making money from early mining. Here's ZCash right now, down about 99% from the initial price.[1] The market cap keeps rising as the price falls, indicating it is being mined way too fast for the market.

[1] https://coinmarketcap.com/currencies/zcash/

Agree with the analysis, puzzles me why the currency doesn't balance the cost of mining in a way that doesn't significantly devalue existing holdings. It would be interesting to see an estimate of the cost to mine the coins at the rate they're being mined. If the cost is more than the face value of the coin, seems like something funny is going on.

>> "The number of people who really understand zk-SNARKs, and therefore the Zcash protocol, is probably small enough that you could feed them all with one Thanksgiving turkey."

If the list is so small, who are they?

More importantly, where are they having this turkey?

In all seriousness though, if I were one of a handlful of people who understood a rising anonymous currency platform, I wouldn't want to be publicly exposed that way.

Indeed, even though a couple popular cryptographers have vouched, it's still not the classic definition of peer-reviewed for something that ground-breaking.

That aside, the MPC (Multi-Party Computation) setup is more of a security theater than actual security. It completely goes against of what cryptography is all about and I'm puzzled as to why any cryptographer would base their system's security in such a way.

Do you mean to say the Zcash trusted setup shouldn't have used MPC? Or do you mean to say Zcash itself is fudnementally flawed due to the trusted setup?

The second one mainly. There is probably a way to do MPC in a truly trustless manner but that's another big challenge and Zcash investors were probably getting impatient so they pushed for a launch.

It actually is the classic definition of peer reviewed! The paper on Zerocash (renamed Zcash) was published at the IEEE Symposium on Security and Privacy:

http://zerocash-project.org/media/pdf/zerocash-oakland2014.p...

It's a peer-reviewed conference and basically the top venue (along with Usenix Security and ACM CCS) for academic computer security.

I'm not sure what you mean by "for something that ground-breaking"?

Oakland is more of a systems security conference, so peer review here speaks more to the architectural thinking, and says little about the deeper math. Same thing for Usenix. I'd want to see somewhere like Crypto/EuroCrypt, or maybe IACR, to call it peer reviewed. Even then, it may pass largely on novelty & prestige.

(For background, I used to publish at this conference and others, did my share of paper reviewing, and my colleagues were working on e-cash crypto around the time of bitcoin's rise.)

My impression with Crypto is that people who focus more on the applied side of cryptography have found it difficult to get papers accepted there.

[My own background is firmly in systems security – I've had papers at Oakland and CCS – and I'm not as familiar with the crypto side]

zkSNARKS, the underlying tricky bit of crypto that Zerocash uses to make anonymous transactions, existed before Zerocash/Zcash. There is a bunch of work on them that was published in Eurocrypt/Crypto/TCC etc. For example [0] at Eurocrypt and [1] at Crypto. Page 37 of that last paper [2] has a summary of work on the subject, though it is now dated as the paper is from 2013.

SNARKs have gotten the appropriate peer review from the right parts of academia. To everyone else reading this: Of course, that doesn't make it secure and there are limmits to peer review. Just because 3 to 5 reviewers read the paper and thought it was publishable doesn't mean it's correct. However, those works were high enough profile that others have looked at the papers once they were published, which is the real meaningful part of peer review and that comes after publication.

None the less, snarks are one of the more sophisticated cryptogrphic techniques ever deployed. And peer review also says abosultely nothing about the security of the implimentations of software instantiating the cryptography. But the only way to remidy that is to build software, deploy it, and get people to look at it.

Zerocash itself is a fairly simple protocol built on top of SNARKs, so the fact that it was published at Oakland isn't the biggest worry. It's also gotten a bunch of scrutiny after that.

[0] http://link.springer.com/chapter/10.1007/978-3-642-38348-9_3... [1] http://link.springer.com/chapter/10.1007/978-3-642-40084-1_6... [2] https://eprint.iacr.org/2013/507.pdf

Probably the authors of the Zerocash paper (http://zerocash-project.org/paper), the authors of the Zcash protocol (https://github.com/zcash/zips/blob/master/protocol/protocol....) and str4d.

Thanks for confirming that you rushed unproven, untested cryptography into a production system meant to defend user's privacy and their money.

Speaking of - why did you rush it out? Because your investors wanted to make profit? Absolutely despicable.

I went to the EE380 talk at Stanford where Eran Tromer explained the theory.[1][2] The claims were very broad, and I didn't understand exactly what was supposed to have been proven. A lot of material was covered very fast. Watch the video and try to figure it out.

[1] http://web.stanford.edu/class/ee380/ [2] https://www.youtube.com/watch?v=KP8TPeYQyN4

This is a prerelease for our soon to be published: "zk-SNARK explained: basic principles" here: https://drive.google.com/file/d/0B57LWnAurZr_OGhVOENnbHRoaGM...

Do you guys know of a decent overview website for all these new hipster currencies?

But I mean a realistic one, including info such as: - how much it has been pre-mined. - why is it being pushed ( research, corp goals, etc) - limits (does one need a GPU to use it or can it execute on a CPU)

I know of few places that have lists, but I get the impression that people start currencies lately as a shot at getting rich if they take off, and not from a realistic need to do so.

Zcash is materially different than Bitcoin, so it at least isn't any more hipster than Bitcoin itself.

Unlike Bitcoin, Zcash transactions can be shielded to hide the sender, recipient, and value of all transactions on the blockchain.

https://z.cash/

It uses completely unproven cryptography that may quite possibly be horribly broken. If you have a better definition of "hipster" than "use something for the sake of it, regardless of practicality" I'd love to hear it.

Oh, I will continue to own $0 in Zcash, but trying to provide actual confidential transactions isn't "for the sake of it, regardless of practicality", there is a clear motivation.

No, it is. Those already exist in the form of Monero. Using some new-fangled, likely broken cryptography, is very hipster.

IMHO the biggest privacy-breaking problem of Monero is that it leaks the transaction amounts, while Zcash does not. Monero also has other inconvenients compared to Zcash: https://www.reddit.com/r/Monero/comments/41vg68/monero_vs_zc...

So you can't claim Monero already solved all the problems that Zcash is trying to solve.

That's incorrect, Monero does not leak amounts since they created and added RingCT (currently compulsory on testnet, and compulsory on mainnet from a hard fork next year September) - https://lab.getmonero.org/pubs/MRL-0005.pdf

Not only does Monero already do what ZCash is trying to do, but it has two main advantages:

1. EVERY transaction is private, which means that the entropy of the anonymityset is continuously growing. Instead, ZCash restricts privacy to an opt-in mechanism (mostly due to private transactions being horrible - requiring north of 8gb of RAM and several minutes on a modern computer) which means that there is a trivial amount of entropy, and deanonymization is pretty trivial.

2. Monero is focusing on further improvements that ZCash is just dreaming about, such as their C++ i2p router, Kovri. They can do this because they've been in production, tested, and hammered for several years.

The real question is: what does ZCash provide that Monero doesn't, except some sort of ridiculous "star cred"?

Monero doesn't already do what Zcash is doing. As you point out yourself, it will be "next year September" that RingCT will be live.

I agree with your other criticism of Zcash though. The situation is far from perfect.

No, it'll be MANDATORY from next year September, not LIVE from next year September...

http://zerocash-project.org/media/pdf/zerocash-extended-2014...

Reply on news.ycombinator.com