Topic: Why the fuck did Satoshi implement the 1 MB blocksize limit? (Read 2188 times)

That isn't going to be happening, the best strategy with your posts is to skim-read them until one finds the deliberate errors you try to promote as facts

SPV clients cannot validate the rules of the network and will hence be able to be tricked into a block with valid PoW but with differing rules from the reference clients. They are hence invalid as per full nodes which validates the full block. (I'm not talking about the merkel root part but the part which you said that nobody cares about the validity of a transaction.)

Since SPV clients blindly follow the chain with the longest valid PoW, it isn't that hard to cheat a SPV client.

No disagreements here.
Your client assumes the chain with the longest PoW as the correct chain. If this happens, isn't your SPV client vulnerable?
A full node is vulnerable to a 51% attack definitely. But isn't your point about a block which violates the protocol rules? If anything, that block isn't valid.

And that begs the question: How do you get the latest headers, with a certainty that it is valid.

Sigh.  Go back and read everything.  

I just realized you missed a crucial point of SPV here: the SPV user has the full list of block headers, but not of the block bodies.  As such, for this user to believe the Electrum server, the root of the given Merkle tree needs to be in one of the elements of the full list of block headers, which means it is part of the block chain "up to now".  I explained that earlier:


Here, H is the full list of block headers.

Edit:
see for instance: http://docs.electrum.org/en/latest/spv.html#spv

That isn't what he said, and you know it.


dinofelis, your only discernible input on this forum is misrepresenting facts in a (kind of) subtle way. Well, you're also good at avoiding direct debunking of the things you say which aren't true.

You ought really to be banned, as it's too obvious that you're not interested in any kind of constructive debate, and never have been (unfortunately, dinofelis is likely the owner of many accounts that have been created with a suspiciously similar style of debate, only adding to the perception that the owner is very intent on wasting everyone's time on Bitcointalk.org)

No, that is cryptographically impossible.  You cannot give a "fraudulent copy of the block chain headers" to an SPV user, if that user knows the currently actual block chain headers, in exactly the same way full nodes do.  In as much as full nodes can know the latest few block headers, an SPV user can know them too, and in as much as you can trick an SPV user into believing the last few block headers are different from what is actually mined on right now, you can just as well trick a full node into that.

Moreover, "tricking someone into a false block chain header list" requires you in any case to spend PoW on that block chain header list of the same order of magnitude than the prong you want your SPV victim to believe.  If you do that, you can just as well trick a full node into your prong.


No, as I outlined, that is not possible.  In order to trick me into believing that, you have to provide me with of course the fake transaction, but you also have to provide me with the leg of the Merkle tree that connects its root to the transaction.  That Merkle root is included in the block chain header list I have.

If that header list is ending on the block chain headers that mining pools are currently mining on, then I know that that transaction is a part of the very block chain miners are mining on right now.  That is exactly the same block chain that full nodes have right now also.

Again: if, of two block chains, the leading heads of the header blocks are the same, both the ENTIRE BLOCK CHAINS are identical.

So there's no such thing as a rogue SPV server, IF I can have access to the latest block headers being mined right now.  And even if I cannot have access to the latest blocks being mined (and then, my full node wouldn't get access either), that "rogue SPV server" still has to spend a lot of PoW to make the false prong.  He will have to spend as much PoW grossly as attacking the real chain, and for this attack to succeed, he must also ensure himself to avoid me of learning about the real chain (that may have somewhat more PoW).   A full node is just as "vulnerable" to such an attack.

There is no more a rogue SPV server, than there can be another rogue document server of a document of which I know the hash.  If I know the hash of a given piece of software, then no server can trick me in installing another piece of software.  As the last block header mined is equivalent to a kind of hash of the entire block chain, no-one is going to be able to serve me anything else and make me believe it.  
However, the structure of the block chain makes it possible to "chop up" the document in small pieces: the transactions.  That's exactly why Satoshi did so.

If I can know the latest headers, I cannot be tricked into accepting anything in the block chain that a full node that is accepting these latest headers, wouldn't have accepted either.

The argument that achow101 put forward, was another situation, namely where in the actual chain, there were double spends included.  Indeed, as an SPV node, I can be made aware of an existing transaction in the actual chain, but I cannot know that that actual chain also includes a double spend, while a full node can.  But then, as I said, bitcoin is broken already.


Just to be absolutely clear: in the SPV system, the SPV user has the full block header chain of course, from the genesis block up to the current blocks.
He simply doesn't have the block bodies.  But he has all the headers.

Nope, you've misconstrued what they've said.  They're saying that SPV users rely on someone to give them a correct copy of the blockchain because SPV clients are not checking the history to validate if what they've received is correct.  The theoretical double spend wouldn't be in the actual blockchain that everyone else can see, it would be in the fraudulent copy being given to the SPV user.  Read what achow101 said again:


You could think you had received some BTC from a transaction, but when you tried to spend it, the rest of the network wouldn't validate it because you didn't actually have the funds, despite the copy of the blockchain you received saying you do have the funds.  SPV users have to rely on honest nodes.

The problem is that you didn't even understand the logic of the arguments here.

Achow101 argued that a risk of using SPV is that one could be tricked in accepting a transaction that was present in the correct block chain that was at the same time a double spend.  In order for that to be a risk, you have to accept already that there HAS BEEN a double spend somewhere in a past block that is included in the current block chain on which everyone is building.  It means hence, that there was a past block (say, block number 506072) that contains a double spend, and that miners are still happily building on top of that.  Otherwise, the SPV user cannot be tricked in believing such a double spend, because it is not present in the block chain.  So one needs to reason as if that were the case.

Achow101's argument is that if such were the block chain, that my SPV client could be tricked in accepting that double spend as true.  That is correct.  My SPV client could indeed simply be convinced that, as it stands, a given transaction was indeed, in the actual block chain and I wouldn't know that it was a double spend that miners had simply accepted.  

MY argument, like yours BTW, if you could think somewhat logically, is that if ever that were the case, then bitcoin is broken.  It means that already for a week or so, there is an invalid block in the chain, and miners don't mind, exchanges don't mind, nobody minds.

Now, if ever that were true, that is, if miners did include a double spend in block 506072 and continued to mine on top of that, then every full node would come to a full stop at block 506071, because they would reject block 506072 as invalid (containing a double spend).  However, as miners have been mining on top of that invalid block 506072 by hypothesis, and are now at block 507762 or so, there is, nowhere in this world, a successor prong to block 506071 that full nodes would accept.  The only blocks that have been made are 506072,506073.... 507762 and are ALL INVALID according to the full node, and no other blocks have ever been made.  So it comes to a full stop, for good.  Because no "good blocks" 506072, 506073,... have ever been mined.

The difficulty with  this kind of argument for a limited mind is that it contains too difficult a form of argument which is called "reductio ad absurdum".  So it is quite normal for some not to be able to follow.    https://en.wikipedia.org/wiki/Reductio_ad_absurdum

I claim that SPV is secure.
Achow101 argues that there is a case where it is insecure.

My argument is: if ever your argument were true, then.... (absurdities) ; which you confirm (!).

Hence, Achow101's argument cannot be valid, and hence my claim that SPV is secure, stands.

Anonymous Kid wrote:  “Why the fuck did Satoshi implement the 1 MB blocksize limit?”

To mess with your head, you vulgar retard, because he hates you personally.  To let us know who the quality posters aren’t, by inciting the creation of trashy megathreads such as this one; he trolled you!  Most of all, to divide the wheat from the tares in the realm of Bitcoin engineering:  People’s blocksize opinions rapidly expose their true (mis)understanding of scaling issues.  Scaling is always a hard engineering problem; and he wanted for it to be easy to spot those who are innately incapable of ever grasping it.

But mostly just to mess with your head, personally, and laugh at you.

(Giving the answer which the question is worth.  I did not need to read more than the subject line to know that this was a stupid thread, which I studiously ignored until it refused to die.  @#$@)

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WRONG.  Invalid transactions do not exist in the blockchain, because they cause the containing block to be rejected as invalid.

Thus highlighting the flaw in premise underlying this ramble of a disorganized thinker:


Yes, miner could fill a block with the output of /dev/random, if he wanted.  However, he would only waste electricity on his own bill; for “Joes [] running nodes in their basement” (as you like to deride nodes) would treat the block as if it were /dev/null.

There is no voting on the Bitcoin network, not “PoW voting” and not otherwise.  Nodes do not blindly follow the chain with highest POW; rather, they follow the chain which is fully valid and independently validated by each of them and has the highest total POW.


Wrong.  The node will ignore the “false block” as if it had never existed.

Such is the power of nodes.

(Now, how’s that for conciseness?)

No, that block header would not be included in the block header list that ends in the last currently published block.  There's no way a malicious electrum server can tell me that a given transaction is in the block chain that ends in the known recent block on which miners are working now.

As I said before, there's no way to make me another block header list than the correct one, that ends in the recent block headers.  I only need to know ONE SINGLE number from the miners: the recent block header hash.  That single hash proves to me that any block header list that ends in that hash, is the actual, right one.  And nobody can lie to me as to any included transaction.  Not even with 90% of all hash rate.  Because there's only ONE SINGLE BLOCK CHAIN that can end in this hash, if the hash function is not broken.

This doesn't even have anything to do with proof of work.  You give me the last header hash, and nobody can lie to me as to anything included in the block chain. Because you cannot lie in a linked list of hashes, you cannot lie in a Merkle tree, and you cannot lie about the hash of a transaction.

Mathematically: even without PoW: if you have two block chains, B and B', build of a chain of headers which contain each the top of a Merkle tree of "data segments", and the top hash of the header list of B is equal to the top hash of the header list of B', then B is identical to B'.

If two tops of header lists are identical, the two lists are identical (up to same length, you could append BEFORE the genesis block, true...).  If the header lists are identical, the roots of the Merkle trees are identical.  And if two Merkle trees are identical, the data segments they hash are identical..

Nobody cares whether the transaction is valid, if it is included in the block chain of course !  The hypothesis of having to check whether transactions that are part of the SOLE current collective consensus might be "wrong" somehow, is making the hypothesis that bitcoin is entirely broken and that nobody gives a shit.

It would mean that miners have made a false block, that all other miners agreed to mine on top of that false block and then on top of that other block and so on.  If a false transaction is deeply burried within the block chain, and miners are still mining on it, and no "clean prong" exists that doesn't include that block, then bitcoin is entirely broken.  Because if that can happen, miners can just include ANYTHING.  They can include erroneously signed transactions, they can include transactions of which the sum of the outputs is 500 times the sum of the inputs, they can include a coin base transaction that gives them 2000 BTC, they can include headers that don't correspond to the Merkle tree, they could include a porn movie, anything.

Moreover, there's not even another block chain in this world that is made correctly, because the massive amount of PoW that goes in this butched-up block chain cannot be re-done elsewhere.  If the massive PoW voting power of the bitcoin miners collectively decide to make a butched-up block chain with false transactions in it, that's all there is to bitcoin, there is no clean version any more.

But even then, SPV is still working, in the following way: it is up to the payer to give you (by e-mail/ftp or other form of communication) the full history of his payment: that is, he has to give you the backward tree of all coinbase transactions and all successive transactions up to his payment to you.  That's quite some data, but unless all coins are mixed up with all other coins, still much, much less than the block chain.  For each transaction in this "pedigree", he needs to specify the block and Merkle tree leg.

With simply the block header list, you can verify the exactitude of his e-mail.  You don't even need an SPV server for that.  You can check the mini-block chain of the pedigree, from the coinbase of each origin at the leaves, all the way up to his last transaction to you.  You don't depend on any form of bitcoin network for that, except that you need to know the head of the current header list.  One single hash you need to know from bitcoin's system, and you can verify all the rest by yourself.

Of course, the payer needs to have all his previous transactions that way.  In other words, if you pay someone, you make a new transaction, you have to watch the bitcoin network in one way or another, and catch your transaction once it is included in a block.  From that, you can extract its SPV data (block header, Merkle leg, transaction).  And you don't care any more about the system.  No need for an extended P2P network.  Only the miner pool servers, or some derived servers from that.

It is true that this way, you cannot be sure that there are no double spends included in the block chain.  But this hassle is only necessary if we take it for granted that bitcoin is already entirely broken, and that miners collectively decide to continue to build a totally broken chain... Indeed, imagine that in the same block, the same coin is spent 500 times to different addresses.  Normally, this cannot happen, but our working hypothesis is that miners make false blocks.  So which one of the 500 transactions is the real one ?  Or is this coin dead now ?

Moreover, in what way would a full node be helpful here ?  A full node would have stopped for good when the first false block was mined.  All full nodes would have come to a grinding halt since a long time, because no miner made a correct block.  They wouldn't be able to tell you anything about recent "valid" transactions on a broken block chain.