added uppercase ascii letters to the variety of characters that could appear...

added uppercase ascii letters to the variety of characters that could appear in urls, but removed visually similar characters from appearing

go/go/models.py

@@ -19,8 +19,21 @@ from django.utils import timezone
 from hashids import Hashids  # http://hashids.org/python/
 
 # generate the salt and initialize Hashids
+# note: the Hashids library already implements several restrictions
+# on character placement, including repeating or incrementing numbers,
+# or placing curse word characters adjacent to one another
+similar_chars = set(['b', 'G', 6,
+                     'g', 'q',
+                     'l', '1', 'I',
+                     'S', '5',
+                     'O', '0',])
+
+alphanumerics = set(string.ascii_letters + string.digits)
+
+link_chars = alphanumerics - similar_chars
+
 HASHIDS = Hashids(
-    salt="srct.gmu.edu", alphabet=(string.ascii_lowercase + string.digits)
+    salt="srct.gmu.edu", alphabet=(link_chars)
 )
 
 class RegisteredUser(models.Model):