Issue #14532: Add a secure_compare() helper to the hmac module, to mitigate
timing attacks. Patch by Jon Oberheide.
diff --git a/Lib/hmac.py b/Lib/hmac.py
index 956fc65..13ffdbe 100644
--- a/Lib/hmac.py
+++ b/Lib/hmac.py
@@ -13,6 +13,27 @@
digest_size = None
+def secure_compare(a, b):
+ """Returns the equivalent of 'a == b', but using a time-independent
+ comparison method to prevent timing attacks."""
+ if not ((isinstance(a, str) and isinstance(b, str)) or
+ (isinstance(a, bytes) and isinstance(b, bytes))):
+ raise TypeError("inputs must be strings or bytes")
+
+ if len(a) != len(b):
+ return False
+
+ result = 0
+ if isinstance(a, bytes):
+ for x, y in zip(a, b):
+ result |= x ^ y
+ else:
+ for x, y in zip(a, b):
+ result |= ord(x) ^ ord(y)
+
+ return result == 0
+
+
class HMAC:
"""RFC 2104 HMAC class. Also complies with RFC 4231.