commit ff5317e99bc8e3f1e7e9727c1208d46e595e67ac
author Janos Follath <janos.follath@gmail.com> Sun Oct 25 12:29:13 2015 +0100
committer Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Fri Jan 08 15:19:14 2016 +0100
tree 843668d8a54f47e4eac4e800d2dad9b0e1044c42
parent 87f14948095f4614acd686f5238933c344174c25

Improved on the fix of #309 and extended the test to cover subroutines.

library/bignum.c

diff --git a/library/bignum.c b/library/bignum.c
index 73ea453..8223b4c 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -893,12 +893,19 @@
 
     if( X == B )
     {
-        const mpi *T;
+        if( B == A )
+        {
+            // Making a temporary copy instead of shifting by one to deny
+            // the possibility of corresponding side-channel attacks.
+            mpi TB;
 
-        if( B == A)
-            return mpi_shift_l( X, 1 );
+            mpi_init( &TB );
+            MBEDTLS_MPI_CHK( mpi_copy( &TB, B ) );
 
-        T = A; A = X; B = T;
+            return mpi_add_abs( X, A, &TB );
+        }
+
+        B = A; A = X;
     }
 
     if( X != A )