Source
r/Bitcoin•
basic_user321

Is a mqn in the middle attack possible for a newly hashed block?

I want to discuss a theory that it mightbe possible to intercept a new hash for the next block before it has been broadcasted to other nodes and thus - steal the block reward by broadcasting the hash faster.

When a miners hashing work has been done and a sufficient hash has been found it still has to be broadcasted online to claim the block reward.

What does the bitcoin network does to prevent that broadcasted data to be intercepted by a MitM attack?

Posted Apr 21, 2023, 5:44 AM UTC

37
sciencetaco•

Miners don't broadcast the hash. They just broadcast the block itself. Nodes independently hash the block and determine if the hash is valid.

This video does a better job of explaining it: https://www.youtube.com/watch?v=_160oMzblY8

3
i_love_CRYPTOzoologyredditor for 3 months•

while true, it doesn't answer the question

no, the proposed attack is not possible. explanation:

the block header is hashed to find the pow solution

the block header contains the merkle root

the merkle root is derived from the block's txns, which includes the coinbase txn

if an attacker wants to modify the coinbase txn to steal the block reward, this would change the merkle root => changes the block header => renders the stolen pow solution invalid

8
Quantris•

The bit that says "send the reward to X" is part of that block and that data is included in what is hashed.

So a theoretical MITM that can completely stop that block from getting broadcast would not be able to modify the block to get the reward for themselves (or more precisely: to do that is essentially the same hashing problem that all miners are already trying to solve and having X's block doesn't save them any work).

The broadcast getting stopped would of course still be bad for Miner X so miners certainly do have an interest in making such attacks infeasible (e.g. by having more than one independent route to the network).

3
metalzip•

the block that miners are finding, and the proof of work they calculate, is already from start tailored to the block in which THEY get the block reward. doesn't matter who broadcasts it - at most block is never broadcasted (or too late) and then they do not get reward, but no one else can get their reward by knowing the block faster than rest of world

2
dlq84•

No. Because the hash is specific to the block, it can't be applied to any other block. And that specific block has the miners Bitcoin address as the UTXO for the Coinbase (not to be confused with the CEX).

2
po00on•

The miner who found the hash includes his wallet address as part of the block, in what's known as the coinbase transaction. This is the wallet address to which the block reward will be sent.If an attacker wanted to steal the block reward, he would have to change the coinbase transaction, within the block, which in turn would invalidate the proof-of-work hash. In other words, he would have to mine the block again, himself, from scratch.

2
igadjeed•

Bitcoin doesn't work like that. The miner does not broadcast the hash. The miner broadcasts the whole block

claim the block reward

Bitcoin does not work like that. The reward is not claimed. The reward payment is one of the transactions inside the block

to prevent that broadcasted data to be intercepted by a MitM attack

Bitcoin is not centralized. There is no middle for a man to be in the middle, because there is no center for receiving miners' blocks

The winning miner can send his block to any node. If the block is valid, it gets propagated to more nodes

100 blocks later, the owner of the address stamped on the reward transaction is able to spend it

It is not possible to change the reward address without changing the hash. When the hash changes, the block becomes invalid

2