Blockchain in the Cloud

[mbare]

Because the bitcoin blockchain is getting larger and larger in size people often don't use the original bitcoin client that fully downloads the blockchain to your computer. As I understood the other wallets connect to an online server that has the blockchain on it to be able to connect with the network. Would it be possible for an attacker to upload a different blockchain history to that server so that possibly millions of users would send transactions to a wrong chain or have wrong balances displayed? Has this happened in the past or is this not possible?

[Charles-Tim]

Only what can happen is for attacker's mining hashrates to surpass bitcoin mining hashrates in a way new blocks mined will have to build on the longest chain caused by 51% attack. But that is practically not possible for now, bitcoin has the strongest blockchain.

[LoyceV]

Would it be possible for an attacker to ~

I think this article on Simplified Payment Verification explains it better than I can

[NeuroticFish]

Because the bitcoin blockchain is getting larger and larger in size people often don't use the original bitcoin client that fully downloads the blockchain to your computer. As I understood the other wallets connect to an online server that has the blockchain on it to be able to connect with the network. Would it be possible for an attacker to upload a different blockchain history to that server so that possibly millions of users would send transactions to a wrong chain or have wrong balances displayed? Has this happened in the past or is this not possible?

The blockchain is not just a file all the clients download and go on happily.
The only way the new blockchain would be accepted by other clients would be if that one would be longer (more blocks) and still valid, and for that to happen the "attacker" would have to have bigger hash rate than the current network.

So it is possible, but the current cost of doing that is too big, making it highly unlikely to be performed.
I would give some reading to https://learn.eqonex.com/news/what-51-attack-and-how-much-would-it-cost. It's just one of the first web results, but it seems to cover the mining/blockchain part and the costs too.

[NotATether]

Because the bitcoin blockchain is getting larger and larger in size people often don't use the original bitcoin client that fully downloads the blockchain to your computer. As I understood the other wallets connect to an online server that has the blockchain on it to be able to connect with the network. Would it be possible for an attacker to upload a different blockchain history to that server so that possibly millions of users would send transactions to a wrong chain or have wrong balances displayed? Has this happened in the past or is this not possible?

It is definitely possible, because Bitcoin Core only does a block verification which checks each block that contains valid (i.e. not syntactically malformed) transactions.

A particularly creative attacker could forge 600K blocks of fake transactions (all valid according to consensus rules), but did not actually happen, and put this on a node which serves many SPV clients. These unwitting clients would proceed to download the wrong blockchain history and thus make balances appear and disappear for some users.

This would be only a visual inconvenience though because none of that history is valid as long as more than 50% of the network is using the correct blockchain (as the bad nodes will eventually be cleaned with true history until they reach a minimum).

[franky1]

Because the bitcoin blockchain is getting larger and larger in size people often don't use the original bitcoin client that fully downloads the blockchain to your computer. As I understood the other wallets connect to an online server that has the blockchain on it to be able to connect with the network. Would it be possible for an attacker to upload a different blockchain history to that server so that possibly millions of users would send transactions to a wrong chain or have wrong balances displayed? Has this happened in the past or is this not possible?

yes it is possible(in your hypothetical)
but (in reality) its not like there is just one blockchain in a central cloud which thousands of merchants all link to.
instead its thousands of merchants with thousands of cloud accounts with thousands of blockchains. which then millions of users then use the thousands of merchants.

to cause an issue, a hacker would need to access all cloud services, and all cloud accounts and simultaneously then try to upload thousands of blockchains to each..(emphasis, at the exact same moment)..
yep.. over 400gb needs to be uploaded instantly per account.. multiplied by thousands of instances. at the same time..
GOODLUCK TRYING THAT!

now this is impossible...
because..
those servers you speak of have hundreds of connections to other peers.
and the moment one receives a deceptive chain that does not match their peers chain. boom. the deceptive chain is dropped, rejected. gone

[pooya87]

It depends on the wallet type and its implementation details. Assuming non-custodial wallets:
* Server dependent wallets like Blockchain.com, Blockstream Green, ... connect to a centralized server and the company that controls that server has to run a node and implement protections and if their server is compromised or a vulnerability is found to fool users' software to think the fake server they are connecting to is real, they could be fed fake data (blocks, transactions,  their confirmed state, etc.).

* Server independent wallets such as Electrum, ... can connect to any random full node or a random specialized full node and synchronize that way. These implementations must have additional verification code inside them to verify the data they receive. For example Electrum performs full verification on all block headers and checks it with multiple specialized bitcoin full nodes which makes it impossible to feed it falsified headers.
There are also other ways that an SPV client could verify if a transaction is actually in a block that would prevent attacks where you would give them fake confirmed transactions.

[mbare]

Ok thanks everyone for the reply. It seems to be that maybe it is still important to have the possibilities for a full downloaded blockchain but for daily use it should be safe to use the electrum etc.

[NotATether]

Ok thanks everyone for the reply. It seems to be that maybe it is still important to have the possibilities for a full downloaded blockchain but for daily use it should be safe to use the electrum etc.

It's not really a matter of "daily use" and "the one time each year when you need to make a super secure transaction" but it's more like there should always be a certain number of full nodes running at all times This number should be several times higher than the number of servers (and hence nodes) can be utilized by the most resourseful actor for running Bitcoin Core with false block data.

There are around 10,000 nodes already running in total, and I'm not going to discount the possibility of at least a small portion of them being nefarious (having bad blocks), but it's tiny enough to ensure that you can only use an SPV wallet such as Electrum and not risk seeing wrong balances.

[Zilon]

Because the bitcoin blockchain is getting larger and larger in size people often don't use the original bitcoin client that fully downloads the blockchain to your computer. As I understood the other wallets connect to an online server that has the blockchain on it to be able to connect with the network. Would it be possible for an attacker to upload a different blockchain history to that server so that possibly millions of users would send transactions to a wrong chain or have wrong balances displayed? Has this happened in the past or is this not possible?

No matter the Node that runs the bitcoin software, for a transaction to get confirmation and added to the block it must require a consensus from nodes connected to the bitcoin protocol. If an attacker uploads a transaction containing a different blockchain history definitely it will be seen by all the nodes connected to the network and can't be verified. the Bitcoin ledger is public and doesn't not have a central database so as anyone can run the bitcoin node it makes it even difficult to upload a wrong balance or a central wallet for payment

[pooya87]

There are around 10,000 nodes already running in total, and I'm not going to discount the possibility of at least a small portion of them being nefarious (having bad blocks),

If the number was counted by an honest node then it should be all honest nodes because an honest node would ban any malicious node that sends them invalid blocks. If it is from bitnodes then at least the first couple of pages contain a lot of malicious nodes (mostly spy nodes not necessarily those having bad blocks).

but it's tiny enough to ensure that you can only use an SPV wallet such as Electrum and not risk seeing wrong balances.

Electrum will reject any invalid block headers since it performs full PoW verification on those headers just like a full node would. In other words you can not send fool Electrum into thinking an invalid block is part of the chain.

[Kakmakr]

So in affect.. you need to get more "invalid" nodes out there to replace the amount of valid nodes that are running out there, so that your version of the Blockchain can be seen as the "valid" Blockchain. That will certainly be a very expensive project and it must be almost instantaneous. ...right?

Is that not one of the methods that BCash and previous "Fork" attackers tried with the voting system, during the fork wars? (Running a bunch of nodes on Virtual Cloud servers)

[LoyceV]

Is that not one of the methods that BCash and previous "Fork" attackers tried with the voting system, during the fork wars? (Running a bunch of nodes on Virtual Cloud servers)

Wasn't the voting (signaling) done by miners in the blocks they mined? Adding nodes won't help for that, and adding miners is very expensive.

[pooya87]

So in affect.. you need to get more "invalid" nodes out there to replace the amount of valid nodes that are running out there, so that your version of the Blockchain can be seen as the "valid" Blockchain. That will certainly be a very expensive project and it must be almost instantaneous. ...right?

Wrong. Validity of blocks is not decided based on how many nodes are running. Lets look at things in reverse. From bcash perspective bitcoin blocks are invalid, meanwhile there are far more bitcoin nodes than there are bcash nodes and yet they continue considering bitcoin blocks invalid.

A valid block is a block that YOUR node decides based on the consensus rules it is enforcing.
 

Is that not one of the methods that BCash and previous "Fork" attackers tried with the voting system, during the fork wars? (Running a bunch of nodes on Virtual Cloud servers)

The minimum requirement for creating a fork is a single node run on a single PC (a single CPU) and changing the algorithm to what you like. You can do it right now too on your PC. Copy bitcoin core's code, change the PoW to allow you to mine blocks at a lowest difficulty on your CPU, change anything else you like and start your fork.
As you can see, you don't need voting at all when creating a fork that will be considered an altcoin.

The reason why bcashers ran a lot of nodes on cloud servers was to create the illusion that their shitcoin has good support. Of course that wasn't all they did, they also manipulated the difficulty to create the incentive for miners to mine on that chain and get more reward in total (1000+ bcash blocks per day compared to ~144 bitcoin blocks per day).

[Cookdata]

Ok thanks everyone for the reply. It seems to be that maybe it is still important to have the possibilities for a full downloaded blockchain but for daily use it should be safe to use the electrum etc.

Other nodes are also required by the electrum wallet you are using. When you click on the green network signal, you will get a list of all the nodes to which your wallets are linked. Running your node is a great way to protect your privacy.

[BlackHatCoiner]

As it was occasioned by Kakmakr, it's advisable to mention that democracy, which is the form of governance they describe, isn't the same as with consensus. In elections, you get to either vote for a party specifically, vote what the majority prefers, or simply leave the country. But, consensus is rather a decision you take free-willingly.

Nor the number of nodes neither the number of people who're running nodes matter. All it matters is what you do. If you want to make transactions reversible, change the block subsidy, the difficulty etc., there's nothing stopping you. But, you don't change bitcoin that way. And this applies to everyone, regardless of the percentage, regardless of their economic strength, regardless of their influence. The moment the majority changes a principle, that very moment, they stop being the majority.

In democracy, the BCH users would have to switch back to BTC, because as it seemed, the majority didn't want it. But, in consensus, they can have it; they can switch to BCH V2, BSV etc., if they like. They don't have to care what the others say.

[DaveF]

I have been putting it this way to people who ask. A bit simplified but I think it makes the point:

Miners always control what is going on in terms of what is added and how the blockchain is run.
No miners = no blocks = no blockchain.

Now, without a somewhat good number of nodes out there other issues can happen in terms of broadcasting transactions and other things.
But in the end if the miners do 'X' and everyone else does 'Y' the miners will have a very expensive working blockchain that nobody else uses and the users will have a static blockchain since nobody is mining on it.

Nodes do matter; but in the end they just move data and are very simple to deploy.

-Dave