Generate a TLSA rec
    :param pub: Pub key in PEM format
    :param usage:
    :param selector:
    :param matching:
    :return: TLSA data portion

def tlsa_data(pub, usage, selector, matching):
    '''
    Generate a TLSA rec
    :param pub: Pub key in PEM format
    :param usage:
    :param selector:
    :param matching:
    :return: TLSA data portion
    '''
    usage = RFC.validate(usage, RFC.TLSA_USAGE)
    selector = RFC.validate(selector, RFC.TLSA_SELECT)
    matching = RFC.validate(matching, RFC.TLSA_MATCHING)

    pub = ssl.PEM_cert_to_DER_cert(pub.strip())
    if matching == 0:
        cert_fp = binascii.b2a_hex(pub)
    else:
        hasher = hashlib.new(RFC.TLSA_MATCHING[matching])
        hasher.update(
            pub
        )
        cert_fp = hasher.hexdigest()

    return _rec2data(usage, selector, matching, cert_fp)