protocol – How possible is a double spend assault?

Every supply of data I take a look at that tackles this downside states that any such fraud is actually not possible at finest and extremely infeasible at worst. By my (very restricted) understanding, the success of this assault is definitely all the way down to timing and luck quite than it needing a 51% management of hashing compute. The state of affairs I have been enthusiastic about:

Preliminary State and assumptions:

1. All nodes are at block peak 𝑛
2. No forks exist; all nodes are in consensus
3. Every new block takes the complete usually distributed 10 minutes to substantiate

Fraudulent Block Submission:

1. An attacker efficiently mines a fraudulent block 𝑛+1 and propagates it via the community. This block accommodates the double spend assault transaction, leaving the true transaction within the mempool the place it is rejected as a result of its thought of a spent transaction, due to this fact excluded from any new block
2. Inside a minute or two, the vast majority of the community receives and validates this block.
3. Nodes acknowledge 𝑛+1 because the longest chain and change to mining on prime of it.

Mining Block 𝑛+2:

1. Assume the subsequent block 𝑛+2 takes the complete (usually distributed) 10 minutes to mine after 𝑛+1 has been accepted.
2. Throughout the first 5 minutes, nearly all nodes would have acquired, validated, and began engaged on block 𝑛+1, given the propagation time is usually lower than a few minutes.

Given these situations, this is how the state of affairs unfolds:

Propagation of Block 𝑛+1:

1. As soon as block 𝑛+1 is propagated and validated throughout the community, all sincere nodes will change to the chain ending in 𝑛+1.

Mining Block 𝑛+2:

1. With all nodes engaged on the brand new longest chain, they are going to mine block 𝑛+2 on prime of 𝑛+1.
2. The community can be in consensus that block 𝑛+1 is a part of the primary chain, and thus any new blocks (together with 𝑛+2) can be constructed on prime of 𝑛+1.

On this state of affairs, assuming the fraudulent block 𝑛+1 propagates and is accepted because the longest chain by the vast majority of the community, all subsequent blocks (like 𝑛+2) will certainly be constructed on this chain. In Abstract:

1. Propagation and Validation: Block 𝑛+1 propagates and is validated rapidly (inside a few minutes), main all nodes to change to this chain.
2. Community Consensus: By 5 minutes into the 10-minute block interval, all nodes can be mining on the 𝑛+1 chain as a consequence of its acceptance because the longest chain.
3. Subsequent Blocks: The subsequent block 𝑛+2 is extremely more likely to be mined on prime of 𝑛+1 for the reason that whole community considers 𝑛+1 as a part of the longest chain.

So, if we assume that the above case holds true it appears to me at the least {that a} double spend assault IS fairly possible underneath the proper situations, so what different protections are in place to

1. Stop this taking place within the first place
2. Unwind within the occasion that there are a number of block confirmations subsequently