Distributed.net has brute-forced RC5 messages encrypted with 56 - and 64-bit keys , and now is working on cracking a 72-bit key . Distributed.net has brute-forced RC5 messages encrypted with 56-bit and 64-bit keys , and is working on cracking a 72-bit key ; as of March 2011 , 1.488 % of the keyspace has been searched .