1 files changed, 46 insertions, 0 deletions
diff --git a/python/itsdangerous/_compat.py b/python/itsdangerous/_compat.py
new file mode 100644
index 0000000..2291bce
--- /dev/null
+++ b/python/itsdangerous/_compat.py
@@ -0,0 +1,46 @@
+import decimal
+import hmac
+import numbers
+import sys
+
+PY2 = sys.version_info[0] == 2
+
+if PY2:
+    from itertools import izip
+
+    text_type = unicode  # noqa: 821
+else:
+    izip = zip
+    text_type = str
+
+number_types = (numbers.Real, decimal.Decimal)
+
+
+def _constant_time_compare(val1, val2):
+    """Return ``True`` if the two strings are equal, ``False``
+    otherwise.
+
+    The time taken is independent of the number of characters that
+    match. Do not use this function for anything else than comparision
+    with known length targets.
+
+    This is should be implemented in C in order to get it completely
+    right.
+
+    This is an alias of :func:`hmac.compare_digest` on Python>=2.7,3.3.
+    """
+    len_eq = len(val1) == len(val2)
+    if len_eq:
+        result = 0
+        left = val1
+    else:
+        result = 1
+        left = val2
+    for x, y in izip(bytearray(left), bytearray(val2)):
+        result |= x ^ y
+    return result == 0
+
+
+# Starting with 2.7/3.3 the standard library has a c-implementation for
+# constant time string compares.
+constant_time_compare = getattr(hmac, "compare_digest", _constant_time_compare)