[8445] Fixed redundant calculation of v and s on every login Author: arrai

The SRP-6 specifications clearly say, that v and s are only to be
    calculated on registering a user and changing his password; calculating
    them on every login is plain waste.

--HG--
branch : trunk

src/shared/Auth/BigNumber.cpp

@@ -161,6 +161,11 @@ uint32 BigNumber::AsDword()
     return (uint32)BN_get_word(_bn);
 }
 
+bool BigNumber::isZero() const
+{
+    return BN_is_zero(_bn)!=0;
+}
+
 uint8 *BigNumber::AsByteArray(int minSize)
 {
     int length = (minSize >= GetNumBytes()) ? minSize : GetNumBytes();

src/shared/Auth/BigNumber.h

@@ -74,6 +74,8 @@ class BigNumber
             return t %= bn;
         }
 
+        bool isZero() const;
+
         BigNumber ModExp(const BigNumber &bn1, const BigNumber &bn2);
         BigNumber Exp(const BigNumber &);