Quote from: franky1 on April 02, 2016, 08:49:08 PM

Quote from: knightdk on April 02, 2016, 08:44:37 PM

it will still be able to validate the block and accept it even though it contains non-standard transactions.

= blindly accepting a block that contains data it cannot verify..

can you not atleast wear your impartial hat for 1 minute to see how this can be abused..
EG someone makes a nonstandard tx to pay themselves alot of bitcoins and gets it added to pool that wont check it.

please just take off the fanboy hat for 1 minute. and put on the sceptical, impartial, bug finding, risk analysing hat.. just once

Sure. This is my impartial view of various scenarios that could attempt to exploit this (also the impartial view that I try to post with).

Scenario 1:
A malicious node (not a miner) creates a transaction that is invalid under segwit rules but valid under old rules and broadcasts it to the network.

Result:
Non-upgraded nodes see the transaction and label it non-standard. They don't relay it and reject it. Segwit nodes see the transaction and they find it invalid. They don't relay it and reject it. Segwit miners do the same as the segwit nodes and the transaction is never included into the blockchain.

Scenario 2:
A malcious miner creates a transaction that is invalid under segwit rules but valid under old rules and includes it into a block he mines.

Result:
A non-upgraded node would validate the block and accept it because it is valid under the old rules. The segwit nodes and miners would see it and reject it because it includes an invalid transaction. If we assume that the segwit miners have a majority of the hash power (as it should be when segwit is deployed with a 95% threshold), then the malicious miner cannot keep up with the network and produce a longer blockchain. The rest of the miners would produce blocks that orphan the invalid one and non-upgraded nodes would go back to the correct blockchain after it grows longer than the malicious one.

If we assume that the malicious miner has a majority of the has power, then we have ourselves a 51% attack which we all know is a problem by itself. This attack is made worse since the old nodes could be tricked to believe that those malicious transactions are legit and that miner can basically trick that part of the network into thinking the miner has more money than he actually does.

Short of a 51% attack, I don't see a problem. Do you have any other scenarios you want me to examine?