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You need a margin account with at least 1:100 leverage, alternatively you could trade with a smaller leverage on sites like Poloniex and Bitfinex.
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I really don´t think that there is any exchange or trading site that offers 100:1 leverage with assets that are as
volatile as cryptocurrencies.
E.g. at Bitfinex maximum leverage is 3.3:1 , which is a far cry from 100:1 leverage.
Why would you need 100:1 leverage in the first place? There is serious money to be made with 3:1 or 5:1 leverage (which is possible
at Kraken).