gistfile1.py

from twisted.internet import defer, reactor, task, threads

def someCrypto():
    # Not safe to use Twisted APIs here
    result = hard_rsa_method()
    return result

@defer.inlineCallbacks
def ciao():
    print "antani!"
    a = yield threads.deferToThread(someCrypto)
    # safe to use Twisted APIs here
    ...

task.LoopingCall(ciao).start(0)

reactor.run()