def __init__(self,
                 plaintext=None,
                 protected=None,
                 unprotected=None,
                 aad=None,
                 algs=None,
                 recipient=None,
                 header=None,
                 header_registry=None):
        """Creates a JWE token.

        :param plaintext(bytes): An arbitrary plaintext to be encrypted.
        :param protected: A JSON string with the protected header.
        :param unprotected: A JSON string with the shared unprotected header.
        :param aad(bytes): Arbitrary additional authenticated data
        :param algs: An optional list of allowed algorithms
        :param recipient: An optional, default recipient key
        :param header: An optional header for the default recipient
        :param header_registry: Optional additions to the header registry
        """
        self._allowed_algs = None
        self.objects = dict()
        self.plaintext = None
        self.header_registry = JWSEHeaderRegistry(JWEHeaderRegistry)
        if header_registry:
            self.header_registry.update(header_registry)
        if plaintext is not None:
            if isinstance(plaintext, bytes):
                self.plaintext = plaintext
            else:
                self.plaintext = plaintext.encode('utf-8')
        self.cek = None
        self.decryptlog = None
        if aad:
            self.objects['aad'] = aad
        if protected:
            if isinstance(protected, dict):
                protected = json_encode(protected)
            else:
                json_decode(protected)  # check header encoding
            self.objects['protected'] = protected
        if unprotected:
            if isinstance(unprotected, dict):
                unprotected = json_encode(unprotected)
            else:
                json_decode(unprotected)  # check header encoding
            self.objects['unprotected'] = unprotected
        if algs:
            self._allowed_algs = algs

        if recipient:
            self.add_recipient(recipient, header=header)
        elif header:
            raise ValueError('Header is allowed only with default recipient')
Пример #2
0
    def __init__(self, payload=None, header_registry=None):
        """Creates a JWS object.

        :param payload(bytes): An arbitrary value (optional).
        :param header_registry: Optional additions to the header registry
        """
        self.objects = dict()
        if payload:
            self.objects['payload'] = payload
        self.verifylog = None
        self._allowed_algs = None
        self.header_registry = JWSEHeaderRegistry(JWSHeaderRegistry)
        if header_registry:
            self.header_registry.update(header_registry)
class JWE(object):
    """JSON Web Encryption object

    This object represent a JWE token.
    """
    def __init__(self,
                 plaintext=None,
                 protected=None,
                 unprotected=None,
                 aad=None,
                 algs=None,
                 recipient=None,
                 header=None,
                 header_registry=None):
        """Creates a JWE token.

        :param plaintext(bytes): An arbitrary plaintext to be encrypted.
        :param protected: A JSON string with the protected header.
        :param unprotected: A JSON string with the shared unprotected header.
        :param aad(bytes): Arbitrary additional authenticated data
        :param algs: An optional list of allowed algorithms
        :param recipient: An optional, default recipient key
        :param header: An optional header for the default recipient
        :param header_registry: Optional additions to the header registry
        """
        self._allowed_algs = None
        self.objects = dict()
        self.plaintext = None
        self.header_registry = JWSEHeaderRegistry(JWEHeaderRegistry)
        if header_registry:
            self.header_registry.update(header_registry)
        if plaintext is not None:
            if isinstance(plaintext, bytes):
                self.plaintext = plaintext
            else:
                self.plaintext = plaintext.encode('utf-8')
        self.cek = None
        self.decryptlog = None
        if aad:
            self.objects['aad'] = aad
        if protected:
            if isinstance(protected, dict):
                protected = json_encode(protected)
            else:
                json_decode(protected)  # check header encoding
            self.objects['protected'] = protected
        if unprotected:
            if isinstance(unprotected, dict):
                unprotected = json_encode(unprotected)
            else:
                json_decode(unprotected)  # check header encoding
            self.objects['unprotected'] = unprotected
        if algs:
            self._allowed_algs = algs

        if recipient:
            self.add_recipient(recipient, header=header)
        elif header:
            raise ValueError('Header is allowed only with default recipient')

    def _jwa_keymgmt(self, name):
        allowed = self._allowed_algs or default_allowed_algs
        if name not in allowed:
            raise InvalidJWEOperation('Algorithm not allowed')
        return JWA.keymgmt_alg(name)

    def _jwa_enc(self, name):
        allowed = self._allowed_algs or default_allowed_algs
        if name not in allowed:
            raise InvalidJWEOperation('Algorithm not allowed')
        return JWA.encryption_alg(name)

    @property
    def allowed_algs(self):
        """Allowed algorithms.

        The list of allowed algorithms.
        Can be changed by setting a list of algorithm names.
        """

        if self._allowed_algs:
            return self._allowed_algs
        else:
            return default_allowed_algs

    @allowed_algs.setter
    def allowed_algs(self, algs):
        if not isinstance(algs, list):
            raise TypeError('Allowed Algs must be a list')
        self._allowed_algs = algs

    def _merge_headers(self, h1, h2):
        for k in list(h1.keys()):
            if k in h2:
                raise InvalidJWEData('Duplicate header: "%s"' % k)
        h1.update(h2)
        return h1

    def _get_jose_header(self, header=None):
        jh = dict()
        if 'protected' in self.objects:
            ph = json_decode(self.objects['protected'])
            jh = self._merge_headers(jh, ph)
        if 'unprotected' in self.objects:
            uh = json_decode(self.objects['unprotected'])
            jh = self._merge_headers(jh, uh)
        if header:
            rh = json_decode(header)
            jh = self._merge_headers(jh, rh)
        return jh

    def _get_alg_enc_from_headers(self, jh):
        algname = jh.get('alg', None)
        if algname is None:
            raise InvalidJWEData('Missing "alg" from headers')
        alg = self._jwa_keymgmt(algname)
        encname = jh.get('enc', None)
        if encname is None:
            raise InvalidJWEData('Missing "enc" from headers')
        enc = self._jwa_enc(encname)
        return alg, enc

    def _encrypt(self, alg, enc, jh):
        aad = base64url_encode(self.objects.get('protected', ''))
        if 'aad' in self.objects:
            aad += '.' + base64url_encode(self.objects['aad'])
        aad = aad.encode('utf-8')

        compress = jh.get('zip', None)
        if compress == 'DEF':
            data = zlib.compress(self.plaintext)[2:-4]
        elif compress is None:
            data = self.plaintext
        else:
            raise ValueError('Unknown compression')

        iv, ciphertext, tag = enc.encrypt(self.cek, aad, data)
        self.objects['iv'] = iv
        self.objects['ciphertext'] = ciphertext
        self.objects['tag'] = tag

    def add_recipient(self, key, header=None):
        """Encrypt the plaintext with the given key.

        :param key: A JWK key or password of appropriate type for the 'alg'
         provided in the JOSE Headers.
        :param header: A JSON string representing the per-recipient header.

        :raises ValueError: if the plaintext is missing or not of type bytes.
        :raises ValueError: if the compression type is unknown.
        :raises InvalidJWAAlgorithm: if the 'alg' provided in the JOSE
         headers is missing or unknown, or otherwise not implemented.
        """
        if self.plaintext is None:
            raise ValueError('Missing plaintext')
        if not isinstance(self.plaintext, bytes):
            raise ValueError("Plaintext must be 'bytes'")

        if isinstance(header, dict):
            header = json_encode(header)

        jh = self._get_jose_header(header)
        alg, enc = self._get_alg_enc_from_headers(jh)

        rec = dict()
        if header:
            rec['header'] = header

        wrapped = alg.wrap(key, enc.wrap_key_size, self.cek, jh)
        self.cek = wrapped['cek']

        if 'ek' in wrapped:
            rec['encrypted_key'] = wrapped['ek']

        if 'header' in wrapped:
            h = json_decode(rec.get('header', '{}'))
            nh = self._merge_headers(h, wrapped['header'])
            rec['header'] = json_encode(nh)

        if 'ciphertext' not in self.objects:
            self._encrypt(alg, enc, jh)

        if 'recipients' in self.objects:
            self.objects['recipients'].append(rec)
        elif 'encrypted_key' in self.objects or 'header' in self.objects:
            self.objects['recipients'] = list()
            n = dict()
            if 'encrypted_key' in self.objects:
                n['encrypted_key'] = self.objects.pop('encrypted_key')
            if 'header' in self.objects:
                n['header'] = self.objects.pop('header')
            self.objects['recipients'].append(n)
            self.objects['recipients'].append(rec)
        else:
            self.objects.update(rec)

    def serialize(self, compact=False):
        """Serializes the object into a JWE token.

        :param compact(boolean): if True generates the compact
         representation, otherwise generates a standard JSON format.

        :raises InvalidJWEOperation: if the object cannot serialized
         with the compact representation and `compact` is True.
        :raises InvalidJWEOperation: if no recipients have been added
         to the object.
        """

        if 'ciphertext' not in self.objects:
            raise InvalidJWEOperation("No available ciphertext")

        if compact:
            for invalid in 'aad', 'unprotected':
                if invalid in self.objects:
                    raise InvalidJWEOperation(
                        "Can't use compact encoding when the '%s' parameter"
                        "is set" % invalid)
            if 'protected' not in self.objects:
                raise InvalidJWEOperation(
                    "Can't use compat encoding without protected headers")
            else:
                ph = json_decode(self.objects['protected'])
                for required in 'alg', 'enc':
                    if required not in ph:
                        raise InvalidJWEOperation(
                            "Can't use compat encoding, '%s' must be in the "
                            "protected header" % required)
            if 'recipients' in self.objects:
                if len(self.objects['recipients']) != 1:
                    raise InvalidJWEOperation("Invalid number of recipients")
                rec = self.objects['recipients'][0]
            else:
                rec = self.objects
            if 'header' in rec:
                # The AESGCMKW algorithm generates data (iv, tag) we put in the
                # per-recipient unpotected header by default. Move it to the
                # protected header and re-encrypt the payload, as the protected
                # header is used as additional authenticated data.
                h = json_decode(rec['header'])
                ph = json_decode(self.objects['protected'])
                nph = self._merge_headers(h, ph)
                self.objects['protected'] = json_encode(nph)
                jh = self._get_jose_header()
                alg, enc = self._get_alg_enc_from_headers(jh)
                self._encrypt(alg, enc, jh)
                del rec['header']

            return '.'.join([
                base64url_encode(self.objects['protected']),
                base64url_encode(rec.get('encrypted_key', '')),
                base64url_encode(self.objects['iv']),
                base64url_encode(self.objects['ciphertext']),
                base64url_encode(self.objects['tag'])
            ])
        else:
            obj = self.objects
            enc = {
                'ciphertext': base64url_encode(obj['ciphertext']),
                'iv': base64url_encode(obj['iv']),
                'tag': base64url_encode(self.objects['tag'])
            }
            if 'protected' in obj:
                enc['protected'] = base64url_encode(obj['protected'])
            if 'unprotected' in obj:
                enc['unprotected'] = json_decode(obj['unprotected'])
            if 'aad' in obj:
                enc['aad'] = base64url_encode(obj['aad'])
            if 'recipients' in obj:
                enc['recipients'] = list()
                for rec in obj['recipients']:
                    e = dict()
                    if 'encrypted_key' in rec:
                        e['encrypted_key'] = \
                            base64url_encode(rec['encrypted_key'])
                    if 'header' in rec:
                        e['header'] = json_decode(rec['header'])
                    enc['recipients'].append(e)
            else:
                if 'encrypted_key' in obj:
                    enc['encrypted_key'] = \
                        base64url_encode(obj['encrypted_key'])
                if 'header' in obj:
                    enc['header'] = json_decode(obj['header'])
            return json_encode(enc)

    def _check_crit(self, crit):
        for k in crit:
            if k not in self.header_registry:
                raise InvalidJWEData('Unknown critical header: "%s"' % k)
            else:
                if not self.header_registry[k].supported:
                    raise InvalidJWEData('Unsupported critical header: '
                                         '"%s"' % k)

    # FIXME: allow to specify which algorithms to accept as valid
    def _decrypt(self, key, ppe):

        jh = self._get_jose_header(ppe.get('header', None))

        # TODO: allow caller to specify list of headers it understands
        self._check_crit(jh.get('crit', dict()))

        for hdr in jh:
            if hdr in self.header_registry:
                if not self.header_registry.check_header(hdr, self):
                    raise InvalidJWEData('Failed header check')

        alg = self._jwa_keymgmt(jh.get('alg', None))
        enc = self._jwa_enc(jh.get('enc', None))

        aad = base64url_encode(self.objects.get('protected', ''))
        if 'aad' in self.objects:
            aad += '.' + base64url_encode(self.objects['aad'])

        cek = alg.unwrap(key, enc.wrap_key_size, ppe.get('encrypted_key', b''),
                         jh)
        data = enc.decrypt(cek, aad.encode('utf-8'), self.objects['iv'],
                           self.objects['ciphertext'], self.objects['tag'])

        self.decryptlog.append('Success')
        self.cek = cek

        compress = jh.get('zip', None)
        if compress == 'DEF':
            self.plaintext = zlib.decompress(data, -zlib.MAX_WBITS)
        elif compress is None:
            self.plaintext = data
        else:
            raise ValueError('Unknown compression')

    def decrypt(self, key):
        """Decrypt a JWE token.

        :param key: The (:class:`jwcrypto.jwk.JWK`) decryption key.
        :param key: A (:class:`jwcrypto.jwk.JWK`) decryption key or a password
         string (optional).

        :raises InvalidJWEOperation: if the key is not a JWK object.
        :raises InvalidJWEData: if the ciphertext can't be decrypted or
         the object is otherwise malformed.
        """

        if 'ciphertext' not in self.objects:
            raise InvalidJWEOperation("No available ciphertext")
        self.decryptlog = list()

        if 'recipients' in self.objects:
            for rec in self.objects['recipients']:
                try:
                    self._decrypt(key, rec)
                except Exception as e:  # pylint: disable=broad-except
                    self.decryptlog.append('Failed: [%s]' % repr(e))
        else:
            try:
                self._decrypt(key, self.objects)
            except Exception as e:  # pylint: disable=broad-except
                self.decryptlog.append('Failed: [%s]' % repr(e))

        if not self.plaintext:
            raise InvalidJWEData('No recipient matched the provided '
                                 'key' + repr(self.decryptlog))

    def deserialize(self, raw_jwe, key=None):
        """Deserialize a JWE token.

        NOTE: Destroys any current status and tries to import the raw
        JWE provided.

        :param raw_jwe: a 'raw' JWE token (JSON Encoded or Compact
         notation) string.
        :param key: A (:class:`jwcrypto.jwk.JWK`) decryption key or a password
         string (optional).
         If a key is provided a decryption step will be attempted after
         the object is successfully deserialized.

        :raises InvalidJWEData: if the raw object is an invaid JWE token.
        :raises InvalidJWEOperation: if the decryption fails.
        """

        self.objects = dict()
        self.plaintext = None
        self.cek = None

        o = dict()
        try:
            try:
                djwe = json_decode(raw_jwe)
                o['iv'] = base64url_decode(djwe['iv'])
                o['ciphertext'] = base64url_decode(djwe['ciphertext'])
                o['tag'] = base64url_decode(djwe['tag'])
                if 'protected' in djwe:
                    p = base64url_decode(djwe['protected'])
                    o['protected'] = p.decode('utf-8')
                if 'unprotected' in djwe:
                    o['unprotected'] = json_encode(djwe['unprotected'])
                if 'aad' in djwe:
                    o['aad'] = base64url_decode(djwe['aad'])
                if 'recipients' in djwe:
                    o['recipients'] = list()
                    for rec in djwe['recipients']:
                        e = dict()
                        if 'encrypted_key' in rec:
                            e['encrypted_key'] = \
                                base64url_decode(rec['encrypted_key'])
                        if 'header' in rec:
                            e['header'] = json_encode(rec['header'])
                        o['recipients'].append(e)
                else:
                    if 'encrypted_key' in djwe:
                        o['encrypted_key'] = \
                            base64url_decode(djwe['encrypted_key'])
                    if 'header' in djwe:
                        o['header'] = json_encode(djwe['header'])

            except ValueError:
                c = raw_jwe.split('.')
                if len(c) != 5:
                    raise InvalidJWEData()
                p = base64url_decode(c[0])
                o['protected'] = p.decode('utf-8')
                ekey = base64url_decode(c[1])
                if ekey != b'':
                    o['encrypted_key'] = base64url_decode(c[1])
                o['iv'] = base64url_decode(c[2])
                o['ciphertext'] = base64url_decode(c[3])
                o['tag'] = base64url_decode(c[4])

            self.objects = o

        except Exception as e:  # pylint: disable=broad-except
            raise InvalidJWEData('Invalid format', repr(e))

        if key:
            self.decrypt(key)

    @property
    def payload(self):
        if not self.plaintext:
            raise InvalidJWEOperation("Plaintext not available")
        return self.plaintext

    @property
    def jose_header(self):
        jh = self._get_jose_header(self.objects.get('header'))
        if len(jh) == 0:
            raise InvalidJWEOperation("JOSE Header not available")
        return jh
Пример #4
0
class JWS(object):
    """JSON Web Signature object

    This object represent a JWS token.
    """
    def __init__(self, payload=None, header_registry=None):
        """Creates a JWS object.

        :param payload(bytes): An arbitrary value (optional).
        :param header_registry: Optional additions to the header registry
        """
        self.objects = dict()
        if payload:
            self.objects['payload'] = payload
        self.verifylog = None
        self._allowed_algs = None
        self.header_registry = JWSEHeaderRegistry(JWSHeaderRegistry)
        if header_registry:
            self.header_registry.update(header_registry)

    @property
    def allowed_algs(self):
        """Allowed algorithms.

        The list of allowed algorithms.
        Can be changed by setting a list of algorithm names.
        """

        if self._allowed_algs:
            return self._allowed_algs
        else:
            return default_allowed_algs

    @allowed_algs.setter
    def allowed_algs(self, algs):
        if not isinstance(algs, list):
            raise TypeError('Allowed Algs must be a list')
        self._allowed_algs = algs

    @property
    def is_valid(self):
        return self.objects.get('valid', False)

    # TODO: allow caller to specify list of headers it understands
    # FIXME: Merge and check to be changed to two separate functions
    def _merge_check_headers(self, protected, *headers):
        header = None
        crit = []
        if protected is not None:
            if 'crit' in protected:
                crit = protected['crit']
                # Check immediately if we support these critical headers
                for k in crit:
                    if k not in self.header_registry:
                        raise InvalidJWSObject(
                            'Unknown critical header: "%s"' % k)
                    else:
                        if not self.header_registry[k].supported:
                            raise InvalidJWSObject(
                                'Unsupported critical header: "%s"' % k)
            header = protected
            if 'b64' in header:
                if not isinstance(header['b64'], bool):
                    raise InvalidJWSObject('b64 header must be a boolean')

        for hn in headers:
            if hn is None:
                continue
            if header is None:
                header = dict()
            for h in list(hn.keys()):
                if h in self.header_registry:
                    if self.header_registry[h].mustprotect:
                        raise InvalidJWSObject('"%s" must be protected' % h)
                if h in header:
                    raise InvalidJWSObject('Duplicate header: "%s"' % h)
            header.update(hn)

        for k in crit:
            if k not in header:
                raise InvalidJWSObject('Missing critical header "%s"' % k)

        return header

    # TODO: support selecting key with 'kid' and passing in multiple keys
    def _verify(self, alg, key, payload, signature, protected, header=None):
        p = dict()
        # verify it is a valid JSON object and decode
        if protected is not None:
            p = json_decode(protected)
            if not isinstance(p, dict):
                raise InvalidJWSSignature('Invalid Protected header')
        # merge heders, and verify there are no duplicates
        if header:
            if not isinstance(header, dict):
                raise InvalidJWSSignature('Invalid Unprotected header')

        # Merge and check (critical) headers
        chk_hdrs = self._merge_check_headers(p, header)
        for hdr in chk_hdrs:
            if hdr in self.header_registry:
                if not self.header_registry.check_header(hdr, self):
                    raise InvalidJWSSignature('Failed header check')

        # check 'alg' is present
        if alg is None and 'alg' not in p:
            raise InvalidJWSSignature('No "alg" in headers')
        if alg:
            if 'alg' in p and alg != p['alg']:
                raise InvalidJWSSignature('"alg" mismatch, requested '
                                          '"%s", found "%s"' % (alg, p['alg']))
            a = alg
        else:
            a = p['alg']

        # the following will verify the "alg" is supported and the signature
        # verifies
        c = JWSCore(a, key, protected, payload, self._allowed_algs)
        c.verify(signature)

    def verify(self, key, alg=None):
        """Verifies a JWS token.

        :param key: The (:class:`jwcrypto.jwk.JWK`) verification key.
        :param alg: The signing algorithm (optional). usually the algorithm
            is known as it is provided with the JOSE Headers of the token.

        :raises InvalidJWSSignature: if the verification fails.
        """

        self.verifylog = list()
        self.objects['valid'] = False
        obj = self.objects
        if 'signature' in obj:
            try:
                self._verify(alg, key, obj['payload'], obj['signature'],
                             obj.get('protected', None),
                             obj.get('header', None))
                obj['valid'] = True
            except Exception as e:  # pylint: disable=broad-except
                self.verifylog.append('Failed: [%s]' % repr(e))

        elif 'signatures' in obj:
            for o in obj['signatures']:
                try:
                    self._verify(alg, key, obj['payload'], o['signature'],
                                 o.get('protected', None),
                                 o.get('header', None))
                    # Ok if at least one verifies
                    obj['valid'] = True
                except Exception as e:  # pylint: disable=broad-except
                    self.verifylog.append('Failed: [%s]' % repr(e))
        else:
            raise InvalidJWSSignature('No signatures availble')

        if not self.is_valid:
            raise InvalidJWSSignature('Verification failed for all '
                                      'signatures' + repr(self.verifylog))

    def _deserialize_signature(self, s):
        o = dict()
        o['signature'] = base64url_decode(str(s['signature']))
        if 'protected' in s:
            p = base64url_decode(str(s['protected']))
            o['protected'] = p.decode('utf-8')
        if 'header' in s:
            o['header'] = s['header']
        return o

    def _deserialize_b64(self, o, protected):
        if protected is None:
            b64n = None
        else:
            p = json_decode(protected)
            b64n = p.get('b64')
            if b64n is not None:
                if not isinstance(b64n, bool):
                    raise InvalidJWSObject('b64 header must be boolean')
        b64 = o.get('b64')
        if b64 == b64n:
            return
        elif b64 is None:
            o['b64'] = b64n
        else:
            raise InvalidJWSObject('conflicting b64 values')

    def deserialize(self, raw_jws, key=None, alg=None):
        """Deserialize a JWS token.

        NOTE: Destroys any current status and tries to import the raw
        JWS provided.

        :param raw_jws: a 'raw' JWS token (JSON Encoded or Compact
         notation) string.
        :param key: A (:class:`jwcrypto.jwk.JWK`) verification key (optional).
         If a key is provided a verification step will be attempted after
         the object is successfully deserialized.
        :param alg: The signing algorithm (optional). usually the algorithm
         is known as it is provided with the JOSE Headers of the token.

        :raises InvalidJWSObject: if the raw object is an invaid JWS token.
        :raises InvalidJWSSignature: if the verification fails.
        """
        self.objects = dict()
        o = dict()
        try:
            try:
                djws = json_decode(raw_jws)
                if 'signatures' in djws:
                    o['signatures'] = list()
                    for s in djws['signatures']:
                        os = self._deserialize_signature(s)
                        o['signatures'].append(os)
                        self._deserialize_b64(o, os.get('protected'))
                else:
                    o = self._deserialize_signature(djws)
                    self._deserialize_b64(o, o.get('protected'))

                if 'payload' in djws:
                    if o.get('b64', True):
                        o['payload'] = base64url_decode(str(djws['payload']))
                    else:
                        o['payload'] = djws['payload']

            except ValueError:
                c = raw_jws.split('.')
                if len(c) != 3:
                    raise InvalidJWSObject('Unrecognized representation')
                p = base64url_decode(str(c[0]))
                if len(p) > 0:
                    o['protected'] = p.decode('utf-8')
                    self._deserialize_b64(o, o['protected'])
                o['payload'] = base64url_decode(str(c[1]))
                o['signature'] = base64url_decode(str(c[2]))

            self.objects = o

        except Exception as e:  # pylint: disable=broad-except
            raise InvalidJWSObject('Invalid format', repr(e))

        if key:
            self.verify(key, alg)

    def add_signature(self, key, alg=None, protected=None, header=None):
        """Adds a new signature to the object.

        :param key: A (:class:`jwcrypto.jwk.JWK`) key of appropriate for
         the "alg" provided.
        :param alg: An optional algorithm name. If already provided as an
         element of the protected or unprotected header it can be safely
         omitted.
        :param protected: The Protected Header (optional)
        :param header: The Unprotected Header (optional)

        :raises InvalidJWSObject: if no payload has been set on the object,
                                  or invalid headers are provided.
        :raises ValueError: if the key is not a :class:`JWK` object.
        :raises ValueError: if the algorithm is missing or is not provided
         by one of the headers.
        :raises InvalidJWAAlgorithm: if the algorithm is not valid, is
         unknown or otherwise not yet implemented.
        """

        if not self.objects.get('payload', None):
            raise InvalidJWSObject('Missing Payload')

        b64 = True

        p = dict()
        if protected:
            if isinstance(protected, dict):
                p = protected
                protected = json_encode(p)
            else:
                p = json_decode(protected)

        # If b64 is present we must enforce criticality
        if 'b64' in list(p.keys()):
            crit = p.get('crit', [])
            if 'b64' not in crit:
                raise InvalidJWSObject('b64 header must always be critical')
            b64 = p['b64']

        if 'b64' in self.objects:
            if b64 != self.objects['b64']:
                raise InvalidJWSObject('Mixed b64 headers on signatures')

        h = None
        if header:
            if isinstance(header, dict):
                h = header
                header = json_encode(header)
            else:
                h = json_decode(header)

        p = self._merge_check_headers(p, h)

        if 'alg' in p:
            if alg is None:
                alg = p['alg']
            elif alg != p['alg']:
                raise ValueError('"alg" value mismatch, specified "alg" '
                                 'does not match JOSE header value')

        if alg is None:
            raise ValueError('"alg" not specified')

        c = JWSCore(alg, key, protected, self.objects['payload'],
                    self.allowed_algs)
        sig = c.sign()

        o = dict()
        o['signature'] = base64url_decode(sig['signature'])
        if protected:
            o['protected'] = protected
        if header:
            o['header'] = h
        o['valid'] = True

        if 'signatures' in self.objects:
            self.objects['signatures'].append(o)
        elif 'signature' in self.objects:
            self.objects['signatures'] = list()
            n = dict()
            n['signature'] = self.objects.pop('signature')
            if 'protected' in self.objects:
                n['protected'] = self.objects.pop('protected')
            if 'header' in self.objects:
                n['header'] = self.objects.pop('header')
            if 'valid' in self.objects:
                n['valid'] = self.objects.pop('valid')
            self.objects['signatures'].append(n)
            self.objects['signatures'].append(o)
        else:
            self.objects.update(o)
            self.objects['b64'] = b64

    def serialize(self, compact=False):
        """Serializes the object into a JWS token.

        :param compact(boolean): if True generates the compact
         representation, otherwise generates a standard JSON format.

        :raises InvalidJWSOperation: if the object cannot serialized
         with the compact representation and `compat` is True.
        :raises InvalidJWSSignature: if no signature has been added
         to the object, or no valid signature can be found.
        """
        if compact:
            if 'signatures' in self.objects:
                raise InvalidJWSOperation("Can't use compact encoding with "
                                          "multiple signatures")
            if 'signature' not in self.objects:
                raise InvalidJWSSignature("No available signature")
            if not self.objects.get('valid', False):
                raise InvalidJWSSignature("No valid signature found")
            if 'protected' in self.objects:
                protected = base64url_encode(self.objects['protected'])
            else:
                protected = ''
            if self.objects.get('payload', False):
                if self.objects.get('b64', True):
                    payload = base64url_encode(self.objects['payload'])
                else:
                    if isinstance(self.objects['payload'], bytes):
                        payload = self.objects['payload'].decode('utf-8')
                    else:
                        payload = self.objects['payload']
                    if '.' in payload:
                        raise InvalidJWSOperation(
                            "Can't use compact encoding with unencoded "
                            "payload that uses the . character")
            else:
                payload = ''
            return '.'.join([
                protected, payload,
                base64url_encode(self.objects['signature'])
            ])
        else:
            obj = self.objects
            sig = dict()
            if self.objects.get('payload', False):
                if self.objects.get('b64', True):
                    sig['payload'] = base64url_encode(self.objects['payload'])
                else:
                    sig['payload'] = self.objects['payload']
            if 'signature' in obj:
                if not obj.get('valid', False):
                    raise InvalidJWSSignature("No valid signature found")
                sig['signature'] = base64url_encode(obj['signature'])
                if 'protected' in obj:
                    sig['protected'] = base64url_encode(obj['protected'])
                if 'header' in obj:
                    sig['header'] = obj['header']
            elif 'signatures' in obj:
                sig['signatures'] = list()
                for o in obj['signatures']:
                    if not o.get('valid', False):
                        continue
                    s = {'signature': base64url_encode(o['signature'])}
                    if 'protected' in o:
                        s['protected'] = base64url_encode(o['protected'])
                    if 'header' in o:
                        s['header'] = o['header']
                    sig['signatures'].append(s)
                if len(sig['signatures']) == 0:
                    raise InvalidJWSSignature("No valid signature found")
            else:
                raise InvalidJWSSignature("No available signature")
            return json_encode(sig)

    @property
    def payload(self):
        if 'payload' not in self.objects:
            raise InvalidJWSOperation("Payload not available")
        if not self.is_valid:
            raise InvalidJWSOperation("Payload not verified")
        return self.objects['payload']

    def detach_payload(self):
        self.objects.pop('payload', None)

    @property
    def jose_header(self):
        obj = self.objects
        if 'signature' in obj:
            if 'protected' in obj:
                p = json_decode(obj['protected'])
            else:
                p = None
            return self._merge_check_headers(p, obj.get('header', dict()))
        elif 'signatures' in self.objects:
            jhl = list()
            for o in obj['signatures']:
                jh = dict()
                if 'protected' in o:
                    p = json_decode(o['protected'])
                else:
                    p = None
                jh = self._merge_check_headers(p, o.get('header', dict()))
                jhl.append(jh)
            return jhl
        else:
            raise InvalidJWSOperation("JOSE Header(s) not available")