It might interest some people here to know that if the EMH were true, you could use it to break unbreakable cryptography.
However that's not what would happen. If you tried it, your crack would fail, and you would just end up proving experimentally that EMH isn't true.
That would move the discussion to "is it true except if you test it in weird experiments though?" which is not an interesting point of debate:
Obviously there are no market participants with infinite wisdom and processing ability who know all public news and factor it into every stock's price instantly at all times, and are perfect in their analysis.
And have been since the dawn of markets, even before the Internet.
it's totally obvious.
Anyway here is a protocol you can use to demonstrate EMH is false, any time you want: