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9 votes

What is a Feeler Connection? When is it used?

A feeler connection is a short-lived outbound connection that only starts up after your node has established the required 8 outbound connections and 2 block-relay-only outbound connections. The ...
  • 291
7 votes
Accepted

How does bitcoin prevent DDoS amplification via the `addr` p2p message type?

For a long time, there was a restriction to strongly prefer connecting to addresses with port 8333. This restriction was recently removed in PR 23542 and PR 23306, although a list of "bad ports&...
  • 456
6 votes

What is a block-relay-only connection? What is it used for?

Block relay connections were added to bitcoin core in v0.19.0.1 in November 2019. Their purpose is to harden the peer-to-peer network against partition attacks. They do this through a clever ...
  • 291
5 votes

Can you get the longest chain by keeping a constant low difficulty?

As Mike and Antoine already explained, we pick the best chain by total accumulated work, not by height, where the work is counted per the blocks' difficulty. However, the original release of Bitcoin ...
  • 65.9k
4 votes
Accepted

How can an attacker change the address to receive someone's reward

So is there any way for the attacker to actually receive the rewards? If the attacker isn't limited by hashrate, then they can obviously just fix the proof of work on the modified block. But at that ...
3 votes

Why does an attacker need 51% mining power to overtake the blockchain?

My understanding is that mining is like a race. This is the misunderstanding. It is more like a sandy beach where someone scattered some small diamonds. The miners rush along the beach repeatedly ...
3 votes

Mining stale low-difficulty blocks as a DoS attack

Bitcoin determines the best chain by choosing the one with the most work. As "work" is a bit nebulous, it is specifically determined using a metric called "chainwork". Chainwork is ...
  • 63.8k
3 votes
Accepted

can the network stagnate if the difficulty grows too big?

In the early days of Bitcoin, sure. Today, not so much. Back when Bitcoin was only being mined by a few individuals on their home PCs, it would have been "relatively" easy to use a ...
3 votes

Can you get the longest chain by keeping a constant low difficulty?

What matters is the cumulative work, not the length of the chain. A block solved at a higher difficulty will add more work than a block (or several blocks for that matter) solved at a lower difficulty....
2 votes

Can you get the longest chain by keeping a constant low difficulty?

Blocks with lower difficulty than the threshold are invalid. Also the “longest” in longest chain doesn’t refer to the number of blocks but to the cumulative difficulty.
  • 3,340
2 votes

Is it possible to realize MitM attack between bitcoin full node and listener of this node?

No, just changing the output value would invalidate the transaction's signatures, which the application can easily verify. But since the application is not a fully validating node, what the attacker ...
2 votes

Mining stale low-difficulty blocks as a DoS attack

Block downloading proceeds in two phases. While they do happen mostly concurrently, it's easier to think of them as separate steps: First, block headers are downloaded from peers, and verified for ...
1 vote

Why does an attacker need 51% mining power to overtake the blockchain?

In short, you don't. But in order to have a probability approaching 1 at time infinity, you need 50% + epsilon. There is actually a table of calculations of the chain lenghth vs overtaking probability ...
1 vote
Accepted

Why does an attacker need 51% mining power to overtake the blockchain?

In a race, an athlete does not need to be faster than 50% of all the athletes combined. He just needs to be the fastest. Mining is simply not analogous to a race. Racers make progress towards the ...
  • 17.6k
1 vote

How does bitcoin prevent DDoS amplification via the `addr` p2p message type?

This specific DDoS vulnerability was exploited in 2021, which lead to an emergency patch. PR #22387 is how Bitcoin prevents DDoS, clients running a version older than v22 may still be used to amplify ...
  • 323
1 vote

Revealing chain earlier when private attack

The chances of a block being reorganized because of a new chaintip displacing the current one drop exponentially as the number of blocks in the current chaintip increases. Since in theory a chain of ...
1 vote

What is the main purpose of the idea PASSPHRASE (25th word)?

Personally I would never let anyone know I had any knowledge of crypto at all. But yes the "deniability wallet" against the $5 wrench attack is one aspect. The BIP39 passphrase should be ...
  • 405
1 vote

what kind of a double spend attack is a career attack?

It might be another name for a race attack See https://www.europeworldnews.com/double-spend-or-double-spend-attack-on-bitcoin-myth-or-reality/ Career attack The Race Attack is a type of duplicate ...
1 vote

What are the various denial of service vectors on the Lightning Network?

This is a draft answer. Alternative answers (as always) are welcome. Alex Bosworth listed a number of DoS vectors on Twitter. This isn't necessarily an exhaustive list. TCP level flooding P2P ...
1 vote

Is there a distinction between an attack and an exploit?

An exploit makes use of a software bug or security vulnerability to induce unintended or unanticipated behavior in software to the attacker's advantage. Neither a Finney attack nor an "empty-...
  • 65.9k

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