From 919b433847da11058840a51e93b29955e2ea5978 Mon Sep 17 00:00:00 2001
From: Brian Wilson <brian@edx.org>
Date: Fri, 30 May 2014 18:34:49 -0400
Subject: [PATCH] Encrypt the session id before writing to tracking logs.

---
 common/djangoapps/track/middleware.py         | 20 +++++++++++++++++--
 .../djangoapps/track/tests/test_middleware.py |  4 ++--
 common/djangoapps/track/views.py              | 11 +++-------
 3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/common/djangoapps/track/middleware.py b/common/djangoapps/track/middleware.py
index e32ee9d4ac..2f7e9eb80b 100644
--- a/common/djangoapps/track/middleware.py
+++ b/common/djangoapps/track/middleware.py
@@ -1,3 +1,5 @@
+import hmac
+import hashlib
 import json
 import re
 import logging
@@ -111,12 +113,26 @@ class TrackMiddleware(object):
         )
 
     def get_session_key(self, request):
-        """Gets the Django session key from the request or an empty string if it isn't found"""
+        """ Gets and encrypts the Django session key from the request or an empty string if it isn't found."""
         try:
-            return request.session.session_key
+            return self.encrypt_session_key(request.session.session_key)
         except AttributeError:
             return ''
 
+    def encrypt_session_key(self, session_key):
+        """Encrypts a Django session key to another 32-character hex value."""
+        if not session_key:
+            return ''
+
+        # Follow the model of django.utils.crypto.salted_hmac() and
+        # django.contrib.sessions.backends.base._hash(), but use MD5
+        # so that the result has the same length (32) as the original
+        # session_key.
+        key_salt = "common.djangoapps.track" + self.__class__.__name__
+        key = hashlib.sha1(key_salt + settings.SECRET_KEY).digest()
+        encrypted_session_key = hmac.new(key, msg=session_key).hexdigest()
+        return encrypted_session_key
+
     def get_user_primary_key(self, request):
         """Gets the primary key of the logged in Django user"""
         try:
diff --git a/common/djangoapps/track/tests/test_middleware.py b/common/djangoapps/track/tests/test_middleware.py
index 1f4dd3b499..3c9a43b181 100644
--- a/common/djangoapps/track/tests/test_middleware.py
+++ b/common/djangoapps/track/tests/test_middleware.py
@@ -117,10 +117,10 @@ class TrackMiddlewareTestCase(TestCase):
         SessionMiddleware().process_request(request)
         request.session.save()
         session_key = request.session.session_key
-
+        expected_session_key = self.track_middleware.encrypt_session_key(session_key)
         context = self.get_context_for_request(request)
         self.assert_dict_subset(context, {
-            'session': session_key,
+            'session': expected_session_key,
         })
 
     def test_request_headers(self):
diff --git a/common/djangoapps/track/views.py b/common/djangoapps/track/views.py
index b3b8cb3998..69be4a37cc 100644
--- a/common/djangoapps/track/views.py
+++ b/common/djangoapps/track/views.py
@@ -41,18 +41,13 @@ def user_track(request):
     except:
         username = "anonymous"
 
-    try:
-        scookie = request.META['HTTP_COOKIE']  # Get cookies
-        scookie = ";".join([c.split('=')[1] for c in scookie.split(";") if "sessionid" in c]).strip()  # Extract session ID
-    except:
-        scookie = ""
-
     page = request.REQUEST['page']
 
     with eventtracker.get_tracker().context('edx.course.browser', contexts.course_context_from_url(page)):
+        context = eventtracker.get_tracker().resolve_context()
         event = {
             "username": username,
-            "session": scookie,
+            "session": context.get('session', ''),
             "ip": _get_request_header(request, 'REMOTE_ADDR'),
             "event_source": "browser",
             "event_type": request.REQUEST['event_type'],
@@ -61,7 +56,7 @@ def user_track(request):
             "page": page,
             "time": datetime.datetime.utcnow(),
             "host": _get_request_header(request, 'SERVER_NAME'),
-            "context": eventtracker.get_tracker().resolve_context(),
+            "context": context,
         }
 
     log_event(event)