The protected header is optional in some cases

Allow the use of a JWE without protected headers.

Thanks to Jan Rusnacko for pointing out this flaw.

Signed-off-by: Simo Sorce <simo@redhat.com>

2 files changed, 30 insertions, 25 deletions

diff --git a/jwcrypto/jwe.py b/jwcrypto/jwe.py
index 40f8edb..a44b7fe 100644
--- a/jwcrypto/jwe.py
+++ b/jwcrypto/jwe.py
@@ -399,8 +399,8 @@ class JWE(object):
         return _aes_gcm(256)
 
     def _jwa(self, name):
-        attr = '_jwa_%s' % name.replace('-', '_').replace('+', '_')
         try:
+            attr = '_jwa_%s' % name.replace('-', '_').replace('+', '_')
             return getattr(self, attr)()
         except (KeyError, AttributeError):
             raise InvalidJWAAlgorithm()
@@ -412,11 +412,24 @@ class JWE(object):
         h1.update(h2)
         return h1
 
+    def get_jose_header(self, header=None):
+        jh = dict()
+        if 'protected' in self.objects:
+            ph = json.loads(self.objects['protected'])
+            jh = self.merge_headers(jh, ph)
+        if 'unprotected' in self.objects:
+            uh = json.loads(self.objects['unprotected'])
+            jh = self.merge_headers(jh, uh)
+        if header:
+            rh = json.loads(header)
+            jh = self.merge_headers(jh, rh)
+        return jh
+
     def add_recipient(self, key, header=None):
         """ Encrypt the provided payload with the given key.
 
         :param key: A JWK key of appropriate type for the "alg"
-                    provided in the 'protected' json string.
+                    provided in the JOSE Headers.
                     See draft-ietf-jose-json-web-key-41
 
         :param header: A JSON string representing the per-recipient header.
@@ -426,16 +439,9 @@ class JWE(object):
         if not isinstance(key, JWK):
             raise ValueError('key is not a JWK object')
 
-        ph = json.loads(self.objects['protected'])
-        if 'unprotected' in self.objects:
-            uh = json.loads(self.objects['unprotected'])
-            ph = self.merge_headers(ph, uh)
-        if header:
-            rh = json.loads(header)
-            ph = self.merge_headers(ph, rh)
-
-        alg = self._jwa(ph.get('alg', None))
-        enc = self._jwa(ph.get('enc', None))
+        jh = self.get_jose_header(header)
+        alg = self._jwa(jh.get('alg', None))
+        enc = self._jwa(jh.get('enc', None))
 
         rec = dict()
         if header:
@@ -450,7 +456,7 @@ class JWE(object):
             if 'aad' in self.objects:
                 aad += '.' + base64url_encode(self.objects['aad'])
 
-            compress = ph.get('zip', None)
+            compress = jh.get('zip', None)
             if compress == 'DEF':
                 data = zlib.compress(self.plaintext)[2:-4]
             elif compress is None:
@@ -537,19 +543,13 @@ class JWE(object):
     # FIXME: allow to specify which algorithms to accept as valid
     def decrypt(self, key, ppe):
 
-        ph = json.loads(self.objects['protected'])
-        if 'unprotected' in self.objects:
-            uh = json.loads(self.objects['unprotected'])
-            ph = self.merge_headers(ph, uh)
-        if 'header' in ppe:
-            rh = json.loads(ppe['header'])
-            ph = self.merge_headers(ph, rh)
+        jh = self.get_jose_header(ppe.get('header', None))
+
         # TODO: allow caller to specify list of headers it understands
-        if 'crit' in ph:
-            self.check_crit(ph['crit'])
+        self.check_crit(jh.get('crit', dict()))
 
-        alg = self._jwa(ph.get('alg', None))
-        enc = self._jwa(ph.get('enc', None))
+        alg = self._jwa(jh.get('alg', None))
+        enc = self._jwa(jh.get('enc', None))
 
         aad = base64url_encode(self.objects.get('protected', ''))
         if 'aad' in self.objects:
@@ -563,7 +563,7 @@ class JWE(object):
         self.decryptlog.append('Success')
         self.cek = cek
 
-        compress = ph.get('zip', None)
+        compress = jh.get('zip', None)
         if compress == 'DEF':
             self.plaintext = zlib.decompress(data, -zlib.MAX_WBITS)
         elif compress is None:
diff --git a/jwcrypto/tests.py b/jwcrypto/tests.py
index 13dfeb7..d66a5b4 100644
--- a/jwcrypto/tests.py
+++ b/jwcrypto/tests.py
@@ -648,3 +648,8 @@ class ConformanceTests(unittest.TestCase):
                           kty='RSA', n=1, key_ops=['sign'], use='enc')
         self.assertRaises(jwk.InvalidJWKValue, jwk.JWK,
                           kty='RSA', n=1, key_ops=['sign', 'sign'])
+
+    def test_jwe_no_protected_header(self):
+        enc = jwe.JWE(plaintext='plain')
+        enc.add_recipient(jwk.JWK(kty='oct', k='A'*32),
+                          '{"alg":"A128KW","enc":"A128GCM"}')