Former Federal Reserve Chairman Alan Greenspan said Bitcoin prices are unsustainably high after surging 89-fold in a year and that the virtual money isn’t currency. “It’s a bubble,” Greenspan, 87, said today in a Bloomberg Television interview from Washington. “It has to have intrinsic value. You have to really stretch your imagination to infer what the intrinsic value of Bitcoin is. I haven’t been able to do it. Maybe somebody else can.” Bitcoins, which exist as software and aren’t regulated by any country or banking authority, surged to a record $1,124.76 on Nov. 30. The currency has rallied on growing interest ... (full story)