EncryptedVote JSON should not contain whitespace

Otherwise the hash displayed in the audited-ballots page will not match
the hash displayed to the user when they prepared their vote.

helios/crypto/electionalgs.py

@@ -340,7 +340,7 @@ class EncryptedVote(HeliosObject):
     return True
 
   def get_hash(self):
-    return utils.hash_b64(utils.to_json(self.toJSONDict()))
+    return utils.hash_b64(utils.to_json(self.toJSONDict(), no_whitespace=True))
 
   def toJSONDict(self, with_randomness=False):
     return {

helios/crypto/utils.py

@@ -15,8 +15,11 @@ def hash_b64(s):
   result= base64.b64encode(hasher.digest())[:-1]
   return result
 
-def to_json(d):
-  return json.dumps(d, sort_keys=True)
+def to_json(d, no_whitespace=False):
+  if no_whitespace:
+    return json.dumps(d, sort_keys=True, separators=(',',':'))
+  else:
+    return json.dumps(d, sort_keys=True)
 
 def from_json(json_str):
   if not json_str: return None