Tasks for 1.6

[NIIBE Yutaka]

On 2013-11-07 at 09:11 +0100, Werner Koch wrote:
> The important thing is that we keep the ABI stable after 1.6.0.

I have one thing not yet in the repository.  It is a test case when
gcry_mpi_powm is called with negative BASE (and a fix).  I think that
it is the bug of old implementation of gcry_mpi_powm.

Here is the patch for the code before new implementation.

On 2013-09-12 at 10:17 +0900, NIIBE Yutaka wrote:
> Well, I wrote a test case to share the issue.  Here is a possible
> patch.  In the test case, it calculates (-17)^6 mod 19.  Result should
> be 7.  Mathematically, it's also correct for powm to return -12 in
> this case, but it checks against positive 7.
> 
> In the current implementation it returns -7, which is wrong.

diff --git a/tests/mpitests.c b/tests/mpitests.c
index e1c51d1..ae206d7 100644
--- a/tests/mpitests.c
+++ b/tests/mpitests.c
@@ -379,6 +379,25 @@ test_powm (void)
   if (gcry_mpi_cmp (res, base))
     die ("test_powm failed at %d\n", __LINE__);
 
+  /* Check for a case: base is negative and expo is even.  */
+  gcry_mpi_set_ui (base, b_int);
+  gcry_mpi_neg (base, base);
+  gcry_mpi_set_ui (exp, e_int * 2);
+  gcry_mpi_set_ui(mod, m_int);
+  gcry_mpi_powm (res, base, exp, mod);
+  /* Result should be positive and it's 7 = (-17)^6 mod 19.  */
+  if (gcry_mpi_is_neg (res) || gcry_mpi_cmp_ui (res, 7))
+    {
+      if (verbose)
+       {
+         fprintf (stderr, "is_neg: %d\n", gcry_mpi_is_neg (res));
+         fprintf (stderr, "mpi: ");
+         gcry_mpi_dump (res);
+         putc ('\n', stderr);
+       }
+      die ("test_powm failed for negative base at %d\n", __LINE__);
+    }
+
   gcry_mpi_release (base);
   gcry_mpi_release (exp);
   gcry_mpi_release (mod);
diff --git a/mpi/mpi-pow.c b/mpi/mpi-pow.c
index 85d6fd8..4955fa5 100644
--- a/mpi/mpi-pow.c
+++ b/mpi/mpi-pow.c
@@ -169,7 +169,7 @@ gcry_mpi_powm (gcry_mpi_t res,
     }
   MPN_COPY ( rp, bp, bsize );
   rsize = bsize;
-  rsign = bsign;
+  rsign = 0;
 
   /* Main processing.  */
   {
@@ -184,7 +184,7 @@ gcry_mpi_powm (gcry_mpi_t res,
     xp = xp_marker = mpi_alloc_limb_space( 2 * (msize + 1), msec );
 
     memset( &karactx, 0, sizeof karactx );
-    negative_result = (ep[0] & 1) && base->sign;
+    negative_result = (ep[0] & 1) && bsign;
 
     i = esize - 1;
     e = ep[i];
--