def _unquote(data):
if not data.startswith(b'<STR_LIT:">') or not data.endswith(b'<STR_LIT:">'):<EOL><INDENT>return data<EOL><DEDENT>return QUOTE_RE.sub(b"<STR_LIT>", data[<NUM_LIT:1>:-<NUM_LIT:1>])<EOL>
Unquote quoted value from DIGEST-MD5 challenge or response.

    If `data` doesn't start or doesn't end with '"' then return it unchanged,
    remove the quotes and escape backslashes otherwise.

    :Parameters:
        - `data`: a quoted string.
    :Types:
        - `data`: `bytes`

    :return: the unquoted string.
    :returntype: `bytes`