Topic: Attack: if I change the genesis block. (Read 2190 times)

Even if clients didn't check the genesis block, you'd still have to make a chain with more proof of work than bitcoin

If you changed the time that a block was mined then the difficulty would change and that would make the rest of the blocks invalid unless their mined blocks are above the target difficulty.
This is why it won't work.

But unlike other altcoins, the private keys would work

a 51% attack is actually when 51% of the mining hashrate/hashpower somehow attacks the network, the most common fear would be to execute a double spend attack.

All that would happen if someone did what the OP proposed is would create a premined altcoin.

The nodes will only accept the chain that has done the most total work as a valid blockchain. If you try to create an alternate blockchain with an earlier genius block then, the total work to mine the blockchain would be lower then the current blockchain and would be rejected.

It is a common misconception that the nodes/network will accept the blockchain with the most number of blocks as the valid blockchain, although this is generally the case when determining if a block is going to be orphaned or not because the competing chains are mining on the same blockchain except a very small number of blocks at the "top" 

Danny explained nicely what would happen. Something like this can't be done.
On the other hand, only 6400 full nodes is a bit worrisome. I find this quite low. Where did you pull this number from?

A good read for anyone running a full node.  I'm going to check my PIX value when I get home (don't know my IP address off the top of my head).  The incentive program looks cool, too.

http://blog.bitcoinfoundation.org/bitnodes-project-2015-q1-report-peer-index-and-incentivized-full-nodes/

Is this where a 51% attack could make this plausible? 1 person broadcasting a block to the network would immediately be rejected but if 5100/10000(for example) broadcast the same fabricated block, this could fool the system, correct?

Danny explained nicely what would happen. Something like this can't be done.
On the other hand, only 6400 full nodes is a bit worrisome. I find this quite low. Where did you pull this number from?

No. Legitimate nodes will never accept a block that is considered invalid, regardless of how many nodes are broadcasting it. In your example, the attacking nodes would form a separate fork and the legit nodes would just carry on with the original blockchain.

You can't do this on 6400 nodes (full nodes !) in less than 2 minutes.

Is this where a 51% attack could make this plausible? 1 person broadcasting a block to the network would immediately be rejected but if 5100/10000(for example) broadcast the same fabricated block, this could fool the system, correct?

I have a question which is probably naive, but I was wondering:

suppose I change the genesis block of the bitcoin block chain, and, very important, I change the time stamp of the genesis block to, say, January 15th 2007.

I now calculate an entirely new block chain from there on, in which i can include all or some of the transactions of the current block chain, but I put time stamps on the blocks so that they are slightly more separated in time than in the original chain.  As such, the difficulty will remain very low, and I can easily calculate such a chain on my PC.
I could include many more blocks on the new chain, than on the original chain, because I have 2 years more "block chain time" to fill up until now.  As long as I separate all the blocks by somewhat more than 10 minutes time stamps, the difficulty will essentially remain 1, and I can very easily mine all the blocks on my PC.  Now, in order to respect most transactions, I would have to use the same addresses of most of the block rewards, but some, I could change and assign them to me.  For instance, I could assign all the Satoshi rewards of the first thousands of blocks to addresses I own, because they have never been spend.

If I catch up to today, with most transactions included, but many more blocks, and I broadcast this new chain, would it replace the old chain (because the one I broadcast is much longer) ?  Of course, lots of strange things would happen, such as the difficulty falling essentially to 1 or so. But strictly speaking, would the bitcoin core accept this new chain over the former one because it respects all the rules ?  Or does the bitcoin core check on the genesis block ?

It checks on the Genesis block AND your chain wouldn't pass the "most proof of work" test for becoming the current chain.

suppose ...