system: You are an expert security code reviewer. You will be shown a source code file along with a multi-select question listing several CWE (Common Weakness Enumeration) categories. Your task is to identify which of the listed CWEs are present in the code.

OUTPUT FORMAT: Respond with the letter(s) of all correct options, sorted alphabetically and comma-separated, wrapped in a single \boxed{...}. Examples: `\boxed{A}` for one correct, `\boxed{A,C}` for two, `\boxed{A,C,E}` for three. Output the boxed answer ONLY -- no explanation, no other text.

user: ```python
try:
    import gzip
except ImportError:
    gzip = None
try:
    import zlib
except ImportError:
    zlib = None
import hashlib
import hmac
import logging
import pickle
import sys

from huey.exceptions import ConfigurationError
from huey.utils import encode


logger = logging.getLogger('huey.serializer')


if gzip is not None:
    if sys.version_info[0] > 2:
        gzip_compress = gzip.compress
        gzip_decompress = gzip.decompress
    else:
        from io import BytesIO

        def gzip_compress(data, comp_level):
            buf = BytesIO()
            fh = gzip.GzipFile(fileobj=buf, mode='wb',
                               compresslevel=comp_level)
            fh.write(data)
            fh.close()
            return buf.getvalue()

        def gzip_decompress(data):
            buf = BytesIO(data)
            fh = gzip.GzipFile(fileobj=buf, mode='rb')
            try:
                return fh.read()
            finally:
                fh.close()


if sys.version_info[0] == 2:
    def is_compressed(data):
        return data and (data[0] == b'\x1f' or data[0] == b'\x78')
else:
    def is_compressed(data):
        return data and data[0] == 0x1f or data[0] == 0x78


class Serializer(object):
    def __init__(self, compression=False, compression_level=6, use_zlib=False,
                 pickle_protocol=pickle.HIGHEST_PROTOCOL):
        self.comp = compression
        self.comp_level = compression_level
        self.use_zlib = use_zlib
        self.pickle_protocol = pickle_protocol or pickle.HIGHEST_PROTOCOL
        if self.comp:
            if self.use_zlib and zlib is None:
                raise ConfigurationError('use_zlib specified, but zlib module '
                                         'not found.')
            elif gzip is None:
                raise ConfigurationError('gzip module required to enable '
                                         'compression.')

    def _serialize(self, data):
        return pickle.dumps(data, self.pickle_protocol)

    def _deserialize(self, data):
        return pickle.loads(data)

    def serialize(self, data):
        data = self._serialize(data)
        if self.comp:
            if self.use_zlib:
                data = zlib.compress(data, self.comp_level)
            else:
                data = gzip_compress(data, self.comp_level)
        return data

    def deserialize(self, data):
        if self.comp:
            if not is_compressed(data):
                logger.warning('compression enabled but message data does not '
                               'appear to be compressed.')
            elif self.use_zlib:
                data = zlib.decompress(data)
            else:
                data = gzip_decompress(data)
        return self._deserialize(data)


def constant_time_compare(s1, s2):
    return hmac.compare_digest(s1, s2)


class SignedSerializer(Serializer):
    def __init__(self, secret=None, salt='huey', **kwargs):
        super(SignedSerializer, self).__init__(**kwargs)
        if not secret or not salt:
            raise ConfigurationError('The secret and salt parameters are '
                                     'required by %r' % type(self))
        self.secret = encode(secret)
        self.salt = encode(salt)
        self.separator = b':'
        self._key = hashlib.sha1(self.salt + self.secret).digest()

    def _signature(self, message):
        signature = hmac.new(self._key, msg=message, digestmod=hashlib.sha1)
        return signature.hexdigest().encode('utf8')

    def _sign(self, message):
        return message + self.separator + self._signature(message)

    def _unsign(self, signed):
        if self.separator not in signed:
            raise ValueError('Separator "%s" not found' % self.separator)

        msg, sig = signed.rsplit(self.separator, 1)
        if constant_time_compare(sig, self._signature(msg)):
            return msg

        raise ValueError('Signature "%s" mismatch!' % sig)

    def _serialize(self, message):
        data = super(SignedSerializer, self)._serialize(message)
        return self._sign(data)

    def _deserialize(self, data):
        return super(SignedSerializer, self)._deserialize(self._unsign(data))

```

Which of the following CWE vulnerability categories are present in this code? Multiple options may be correct.

  A) CWE-20: Improper Input Validation
  B) CWE-943: Improper Neutralization of Special Elements in Data Query Logic
  C) CWE-1004: Sensitive Cookie Without 'HttpOnly' Flag
  D) CWE-327: Use of a Broken or Risky Cryptographic Algorithm
  E) CWE-601: URL Redirection to Untrusted Site ('Open Redirect')
  F) CWE-643: Improper Neutralization of Data within XPath Expressions ('XPath Injection')
Answer: D