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Author Topic: BIP 66 status  (Read 8241 times)
jl2012
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July 04, 2015, 02:34:32 AM
 #41

F2Pool is creating version 3 block but it looks like the pool has not rejected the #363731 version 2 block and is working on top of it.
https://blockchain.info/block/0000000000000000155f2519d35cd5d2869900bcc5093594b27763a0315390b4

Also, it seems blockchain.info doesn't reject version 2 blocks as well, which could create problems to those using its wallet or APIs.

That's why I never use bc.i wallet

But why F2Pool acts like this? They shouldn't use customized code

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jl2012
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July 04, 2015, 02:48:19 AM
 #42

So SPV and old full nodes will see 2 fake confirmations now.

363732 is an empty block. I think F2Pool's code just blindly builds on the v2 363731 without looking at its version.

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Dennis7777
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July 04, 2015, 02:57:47 AM
 #43

So SPV and old full nodes will see 2 fake confirmations now.

363732 is an empty block. I think F2Pool's code just blindly builds on the v2 363731 without looking at its version.

Oh damn, AntPool is doing the same as F2Pool.

If you are on the correct side (rejecting v2 block), the latest block you have should be #363732 00000000000000001242e0216eb113f1c50e4c18ecfbc8b9c0224ec82ec391d6
If you are on the wrong side (not rejecting v2 block), the latest block you have would be #363735.

Any idea how many % of network hashrate do Antpool, F2pool, and all those laggard miners have in total?

windpath
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July 04, 2015, 03:46:25 AM
 #44

P2pool at over 90% Smiley
gmaxwell
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July 04, 2015, 05:18:23 AM
 #45

So SPV and old full nodes will see 2 fake confirmations now.
SPV nodes made it up to 6 bogus confirmations.

There was basically half of the network hashrate extending an invalid chain. Sad
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July 04, 2015, 05:41:05 AM
 #46

So SPV and old full nodes will see 2 fake confirmations now.
SPV nodes made it up to 6 bogus confirmations.

There was basically half of the network hashrate extending an invalid chain. Sad


Enforcement?

Yes....?
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July 04, 2015, 07:04:58 AM
 #47

Yes it's enforced now; at least by the potentially-minority parts of the miners that are actually enforcing any rules at all. Sad
trout (OP)
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July 04, 2015, 10:00:58 AM
 #48

This didn't go very smoothly.
Probably some incentives need to be rethought.

Major pools doing "SPV mining" and trust any block on the longest chain. Really?
That enables pretty obvious attacks  have  a really big disruptive impact.
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July 04, 2015, 10:16:16 AM
 #49

Major pools doing "SPV mining" and trust any block on the longest chain. Really?
That enables pretty obvious attacks  have  a really big disruptive impact.

It is safe if they implement safe guards.

The assumption for SPV mining is that nobody would create invalid blocks.  They still cost the same POW to make, so nobody would bother.

This is a reasonable assumption if it is weakened slightly to "It is very rare for other miners to create invalid blocks".  Even with SPV mining, you need to eventually check that the full block is valid.

By building empty blocks on the longest header chain, the pool doesn't waste hashing power during the window when a new block is being verified.

A <- B <- C <- D <- e

In this case, A, B, C and D are fully validated but the full block for e hasn't been received yet.  The miner only checks POW.

If the pool mines block E', then it is wasting its hashing power.  Even if E' is found, it will be older than e, so will be rejected by the network.

By building an empty block as block F, the hashing power is not wasted.  This is a good thing.

The problem starts if block E (full block for e) was actually invalid.  In that case, we don't want miners building on top of it.

An easy way to accomplish it is to have a timeout.  If you are building empty blocks on block e for more than a minute, assume E was invalid after all and switch back to building on D.

Ties should be broken in favor of the block that is fully validated.

The irony in this case is that the invalid fork could have been detected by only checking the headers, so the full block wasn't even needed anyway.

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trout (OP)
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July 04, 2015, 10:45:11 AM
 #50

Thanks for the explanation.

As far as I understand, this is how SPV mining should be done, but not how it was
in this case.  If the miners trusted the new block only during that short window
while it was being propagated, they wouldn't have built a whole new chain on top of it.
At most one block - which would be disbanded once they verified that the block E
they were building on was wrong.

But they didn't check it at all. They just kept on building.

About the cost of the attack: it costs about 25BTC to mine a block.
If it spends 25 000 BTC of other people's money to the attacker's wallet, then
just >0.1% of success makes it worth it.  If major miners are not checking
blocks at all, that probability of success seems to be much higher.
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July 04, 2015, 12:38:25 PM
 #51

As far as I understand, this is how SPV mining should be done, but not how it was
in this case.

Yes, it looks like they just kept building empty blocks on top of empty blocks.  The 5% which haven't upgraded would be creating blocks with transactions on the invalid chain though.

Quote
If the miners trusted the new block only during that short window
while it was being propagated, they wouldn't have built a whole new chain on top of it.

Right.

Quote
About the cost of the attack: it costs about 25BTC to mine a block.
If it spends 25 000 BTC of other people's money to the attacker's wallet, then
just >0.1% of success makes it worth it.  If major miners are not checking
blocks at all, that probability of success seems to be much higher.

The pools which mined the empty blocks lost money.  In the alert, they say around $50,000 was lost by the pools which were setup correctly.

This is a pretty large incentive to update their code so that it works properly.  If you produce a block that is invalid, then you lose around $6,000 per invalid block.

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July 04, 2015, 07:56:26 PM
 #52

The pools which mined the empty blocks lost money.  In the alert, they say around $50,000 was lost by the pools which were setup correctly.

This is a pretty large incentive to update their code so that it works properly.  If you produce a block that is invalid, then you lose around $6,000 per invalid block.

That's the narrow view.  In the aggregate, Ant/F2's risky/lossy 'unchecked headers-only' hack may be a rational/profitable strategy (back luck with BIP66 collision notwithstanding).

As far as I understand, this is how SPV mining should be done, but not how it was
in this case.

they just kept building empty blocks on top of empty blocks.

From the protocol's POV, the problem wasn't that the fork chain was built on empty blocks, just that those blocks were invalid.


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