Bitcoin is a crypto-currency, cash controlled by mathematics instead of greedy bankers.
I get what you're saying, but I don't think the layman wants their cash controlled by mathematicians either. Nor does the layman want the burden of learning what a crypto-currency might be. How about:
Bitcoin is a currency controlled by
you instead of by a greedy wunch of bankers.
but now that just sounds like an advertising slogan, that even your average joe sixpack will identify as propaganda.