<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def update_file(finfo, sample_info, config):
 """Update the file to an Amazon S3 bucket, using server side encryption. """

    ffinal = filesystem.update_file(finfo, sample_info, config, pass_uptodate=True)
    if os.path.isdir(ffinal):
        to_transfer = []
        for path, dirs, files in os.walk(ffinal):
            for f in files:
                full_f = os.path.join(path, f)
                k = full_f.replace(os.path.abspath(config["dir"]) + "/", "")
                to_transfer.append((full_f, k))
    else:
        k = ffinal.replace(os.path.abspath(config["dir"]) + "/", "")
        to_transfer = [(ffinal, k)]

    region = "@%s" % config["region"] if config.get("region") else ""
    fname = "s3://%s%s/%s" % (config["bucket"], region, to_transfer[0][1])
    conn = objectstore.connect(fname)
    bucket = conn.lookup(config["bucket"])
    if not bucket:
        bucket = conn.create_bucket(config["bucket"], location=config.get("region", "us-east-1"))

    for fname, orig_keyname in to_transfer:
        keyname = os.path.join(config.get("folder", ""), orig_keyname)
        key = bucket.get_key(keyname) if bucket else None
        modified = datetime.datetime.fromtimestamp(email.utils.mktime_tz(
            email.utils.parsedate_tz(key.last_modified))) if key else None
        no_upload = key and modified >= finfo["mtime"]
        if not no_upload:
            _upload_file_aws_cli(fname, config["bucket"], keyname, config, finfo)