[bitcoin-dev] Fraud proofs for block size/weight

[Luke Dashjr <luke@dashjr.org>]

Despite the generalised case of fraud proofs being likely impossible, there 
have recently been regular active proposals of miners attacking with simply 
oversized blocks in an attempt to force a hardfork. This specific attack can 
be proven, and reliably so, since the proof cannot be broken without also 
breaking their attempted hardfork at the same time.

While ideally all users ought to use their own full node for validation (even 
when using a light client for their wallet), many bitcoin holders still do 
not. As such, they are likely to need protection from these attacks, to ensure 
they remain on the Bitcoin blockchain.

I've written up a draft BIP for fraud proofs and how light clients can detect 
blockchains that are simply invalid due to excess size and/or weight:

    https://github.com/luke-jr/bips/blob/bip-sizefp/bip-sizefp.mediawiki

I believe this draft is probably ready for implementation already, but if 
anyone has any idea on how it might first be improved, please feel free to 
make suggestions.

Luke