'Lists the customer master keys.
:type limit: integer
:param limit: Specify this parameter only when paginating results to
indicate the maximum number of keys you want listed in the
response. If there are additional keys beyond the maximum you
specify, the `Truncated` response element will be set to `true.`
:type marker: string
:param marker: Use this parameter only when paginating results, and
only in a subsequent request after you\'ve received a response where
the results are truncated. Set it to the value of the `NextMarker`
in the response you just received.'

def list_keys(self, limit=None, marker=None):

    params = {}
    if (limit is not None):
        params['Limit'] = limit
    if (marker is not None):
        params['Marker'] = marker
    return self.make_request(action='ListKeys', body=json.dumps(params))
