Bitcoin Attacks that Might be a problem - Discussion

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Hi everyone,

I have a question regarding Sybil attacks. @ivan, you mentioned in your video at 1:30 that someone could surround a node. But can someone choose which node they are connecting with? If so, can a node choose how many neighboring nodes it connects to?

Thanks in advance for the additional info!

Hi again,
I wanted to bump my previous question and I also have an additional question:
For Segmentation, you mentioned that whenever that segmentation/barrier goes down, the group that was cut-off will have their blockchain replaced by the outside blockchain.

That being said, we’ve learned in your other courses that “the longest chain wins”. So what happens in a case where a small group of nodes happens to mine blocks at a slightly faster rate than the outside chain? In the case of Segmentation, if the group that’s cut off from the internet maintains a chain that’s slightly longer (due to decreased difficulty and some luck), why would this chain not replace the outside “global” chain?

Edit: The 51% attack video addressed my question above by explaining that you’d need 30-51% of the hashpower to be able to create a longer chain. This makes sense given that network difficulty adjusts every 2016 block (or 2 weeks). By the time it adjusts to this new “fake chain”, the global chain will be much longer and too difficult to catch up to. Even if mining difficulty decreases within this “fake chain” it would only adjust to so that blocks are solved within ~10 minutes on average, so it would never really have the opportunity to catch up to the main chain’s length. Is this the correct response?

Thanks for your insight!