Show HN: Logcoin – Toy crypto-currency based on a zero-knowledge protocol (opens in new tab)

So, what I mean by zero knowledge is that there is zero knowledge of the secret key x, the discrete log of y. Y itself is supposed to be derived, that's part of the protocol. But when Bob randomly offsets the x-value before sending it, he is committing to a value of x, c, and b which he must then verify. It will be impossible for him to verify the c and b if he doesn't know x, which is important (see below).

modp groups are easier to implement, I was look into EC but I may come back to it later.

Bob doesn't want to send y directly because then another man in the middle could, before the transaction times out, forward y, spoof his own b and c, forward the verification of x and then verify his own b and c. Then he cannot spend the coin but he can make it unspendable.

If one tracker is malicious, he'll be out of sync with all the other trackers to which the transaction is also broadcast to. Every single known tracker would need to be compromised (they are all public).

This looks cool!

However, if the tracker is centralized, doesn't protection against double spends basically come for free?

Or, maybe not because of the other things?

Oh, wait, ok so in this situation does the tracker have any privileged information?

It doesn't look like it, So, another party could take the place of the tracker if the tracker went down?

I don't understand the proof of stake bit in the readme. I don't see anything about staking the coin, and I generally don't understand how proof of stake applies to something like this?

No reason to be sorry. well, the title was supposed to be longer :P. I was going to write the same as the github title but it didn't fit. It is clearly a toy---ahermmg---semi-serious theoretical exercise, and not a real competitor to bitcoin or zerocoin, you are right in that respect.

This (as far as I know) does make it impossible to trace the history of a coin, because there is no recorded transaction history, assuming you don't send the transaction details directly from your ip (and valid coin transfers are mathematically impossible to spoof from e.g. an exit node). You also don't need a centralized tracker, you just need a public record of all known coins which is kept in sync across several mirrors. I should clarify that in the readme; the only reason why I mention assuming a centralized tracker is for the performance estimate, because syncing trackers would induce overhead. Unless you see something I am missing...

The reason why this uses zero-knowledge proofs is twofold; first, to allow anonymization of individual transaction ids by ensuring it is impossible to spoof transactions without knowing the secret key of the corresponding coin, and second to avoid the use of a blockchain which further degrades anonymity. Again, it may be that you have discovered a reason why this does not hold, in which case I would be interested to hear it!

Regarding the matter of coin transfer, this was a design decision because of the project scope. I could have spent many days implementing a transaction system which did not depend on the secrecy of keys, but I have other commitments. That being said, there are a subset of transactions (involving money, but also authentication of physical goods in transit, for example) which can potentially be treated this way. For instance, I can use it to verify the user is in possession of a particular hardware (a physical "coin") which stores the secret key in encrypted form. Which could be useful in e.g. shipping applications, who knows.

This comment does seem fairly harsh for something advertised as "a toy." Why would you expect a toy to be state of the art? When I see that phrase, I think of something that is a personal learning experience, might have an interesting idea or two but is not expected to replace anything that already exists.