On Thu, May 18, 2017 at 2:44 PM, Cameron Garnham via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

1.     Significant deviations from the Bitcoin Security Model have been acknowledged as security vulnerabilities.

The Bitcoin Security Model assumes that every input into the Proof-of-Work function should have the same difficulty of producing a desired output.

This isn't really that clear.

Arguably as long as the effort to find a block is proportional to the block difficulty parameter, then it isn't an exploit.  It is just an optimisation.

A quantum computer, for example, could find a block with effort proportional to the square root of the difficulty parameter, so that would count as an attack.  Though in that case, the fix would likely be to tweak the difficulty parameter update calculation.

A better definition would be something like "when performing work, each hash should be independent". 

ASICBOOST does multiple checks in parallel, so would violate that.