def put_uri_extension(data):
    """This block of data contains integrity-checking information (hashes
        of plaintext, crypttext, and shares), as well as encoding parameters
        that are necessary to recover the data. This is a serialized dict
        mapping strings to other strings. The hash of this data is kept in
        the URI and verified before any of the data is used. All buckets for
        a given file contain identical copies of this data.

        The serialization format is specified with the following pseudocode:
        for k in sorted(dict.keys()):
            assert re.match(r'^[a-zA-Z_\\-]+$', k)
            write(k + ':' + netstring(dict[k]))

        @param data=URIExtensionData
        @return: a Deferred that fires (with None) when the operation completes
        """
