The easiest to understand response to this question that I've seen so far is from this comment [0]:
The contest limitations rule out most of the likely attack vectors for breaking the protocol in the real world. It's like saying "Our bank vans are 100% secure. Just try stealing money from them without puncturing our tires or bribing one of our employees."
The contest limitations rule out most of the likely attack vectors for breaking the protocol in the real world. It's like saying "Our bank vans are 100% secure. Just try stealing money from them without puncturing our tires or bribing one of our employees."
[0] - https://news.ycombinator.com/item?id=6936949