In a bombshell move that sent the value of bitcoin tanking Friday, China outlawed all cryptocurrency transactions and issued a national ban on crypto mining, the energy-intensive process of creating new bitcoins. China’s crackdown is fueled by concerns that crypto attracts money laundering and fraud, and that crypto mining uses up so much power it will dent the nation’s efforts to cut greenhouse-gas emissions. China has the most crypto miners in the world, but few speculators given its increasingly strict regulations. In early trading Friday, bitcoin’s value dropped more than 7 percent on the news.