autoconf: only use side-channel secured mpz_powm_sec if it's available (libgmp 5 or later)

1 files changed, 6 insertions, 1 deletions

diff --git a/lib/Crypto/Util/number.py b/lib/Crypto/Util/number.py
index 7be595b..d5d0c08 100644
--- a/lib/Crypto/Util/number.py
+++ b/lib/Crypto/Util/number.py
@@ -26,7 +26,8 @@
 
 __revision__ = "$Id$"
 
-from Crypto.pct_warnings import GetRandomNumber_DeprecationWarning
+from Crypto.pct_warnings import GetRandomNumber_DeprecationWarning, PowmInsecureWarning
+from warnings import warn as _warn
 import math
 
 bignum = long
@@ -35,6 +36,10 @@ try:
 except ImportError:
     _fastmath = None
 
+# You need libgmp v5 or later to get mpz_powm_sec.  Warn if it's not available.
+if _fastmath is not None and not _fastmath.HAVE_DECL_MPZ_POWM_SEC:
+    _warn("Not using mpz_powm_sec.  You should rebuild using libgmp >= 5 to avoid timing attack vulnerability.", PowmInsecureWarning)
+
 # New functions
 from _number_new import *