Quote from: jl777 on February 26, 2016, 06:57:25 AM

Quote from: TPTB_need_war on February 26, 2016, 05:14:37 AM

There is no way to prove that the consensus of the weaker block chain placed those meta-data records in the stronger block chain. There is some meta-data, but it is meaningless, because consensus is the entire challenge of decentralized protocols that require consensus.

Off topic note that per the CAP theorem, Bitcoin forsakes Partition tolerance in order to achieve Consistency and Availability of consensus. You can think of the other block chain as being another partition. We've been discussing these abstract theoretical issues over in the Altcoin Discussion forum in threads such as The Ethereum Paradox, DECENTRALIZED crypto currency (including Bitcoin) is a delusion (any solutions?), and Satoshi didn't solve the Byzantine generals problem. Also include some discussions between monsterer, smooth, and myself in my vaporcoin's thread. So I have the advantage of a few months of discussions about these abstract topics.

So the issue is not time sequence, but the fact that it is hard to know if the weaker chain put the data in there as part of a consensus or as part of an attack?

If that is the issue, I am confused why we care so much about it? The metadata in the altcoin chain refers to the BTC data, so why does it matter who put it there? It either matches the BTC data or it doesnt. If it matches, it creates a verifiable time sequence. If it doesnt match, then it would be ignored. Could you make a simple example that shows how an attacker can bypass the BTC "clock" and double spend?

Because the altcoins are not confirmed spent on the Bitcoin block chain. The altcoin chain is free to disagree with the Bitcoin block chain.

The point about relative ordering of blocks between two chains (i.e. two partitions) is relevant to why it is impossible to enforce that the altcoin chain must follow the Bitcoin block chain's consensus. If you think out how you would attempt to specify a protocol for the altcoin chain so that it must obey the Bitcoin consensus, you will soon realize that it is impossible because no external truth exists in a block chain.

Quote from: jl777 on February 26, 2016, 06:57:25 AM

I dont think using bitcoin as the reference clock violates the CAP theorem as it defines the bitcoin data as definitive source of data, so Consistency is achieved, along with availability. [I dont want to get into whether bitcoin itself has done this or that with byzantine whatchamacallits]

Maybe to solve the Partition part, the metadata for the altcoin metadata needs to get back into the BTC chain. We are talking about a slow process, but even if it takes a day for all the back and forth, it seems that it isnt impossible. I just dont understand what exactly is needed.

Maybe it is like spontaneous creation of life from inert chemicals which is (nearly) impossible [please it is just an example, dont want to get into any creation/evolution debate either!], but once it is there, it is hard to stop it from replication. And kind of hard to deny that it exists. Since we now have bitcoin, maybe building on it allows to achieve the desired result (better altcoin security) without any violation of proven theorems by changing the problem.

James

P.S. CAP seems to vary from principle, conjecture, to theorem based on exact and precise definitions, I dont know if bitcoin is the exactly same behavior as in the proven CAP theorem, or if a bitcoin + extra is unable to change it to be beyond the confines of what is proven. I dont like to fight against math proofs, but if there is any level of abstraction in the proof then it is usually possible to "work around" it by transforming the problem to a different problem that isnt proven impossible. Since I am not trying to disprove the CAP theorem, but rather create a cross chain security mechanism that isnt covered by the CAP theorem proper

Sorry but you will need to read and understand deeply the threads I linked to. We've analyzed this already and it is an inviolable mathematical structure.