[git] GCRYPT - branch, master, updated. libgcrypt-1.5.0-268-g1f5f445

[by Werner Koch]

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      from  df013c9820709421ef9550158ac5df0060d73379 (commit)

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- Log -----------------------------------------------------------------
commit 1f5f4452e5bca105ec2197a4facbf9778e7dc31e
Author: Werner Koch <wk at gnupg.org>
Date:   Sat Sep 7 10:06:46 2013 +0200

    ecc: Fix highly unlikely endless loop in sign_ecdsa.
    
    * cipher/ecc.c (sign_ecdsa): Turn while-do into do-while loops.
    --
    
    Reported-by: Dmitry Eremin-Solenikov
    Signed-off-by: Werner Koch <wk at gnupg.org>

diff --git a/cipher/ecc.c b/cipher/ecc.c
index 82d5bba..0b89ec2 100644
--- a/cipher/ecc.c
+++ b/cipher/ecc.c
@@ -408,21 +408,16 @@ sign_ecdsa (gcry_mpi_t input, ECC_secret_key *skey, gcry_mpi_t r, gcry_mpi_t s,
   x = mpi_alloc (0);
   point_init (&I);
 
-  mpi_set_ui (s, 0);
-  mpi_set_ui (r, 0);
-
   ctx = _gcry_mpi_ec_p_internal_new (skey->E.model, skey->E.dialect,
                                      skey->E.p, skey->E.a, skey->E.b);
 
-  while (!mpi_cmp_ui (s, 0)) /* s == 0 */
+  /* Two loops to avoid R or S are zero.  This is more of a joke than
+     a real demand because the probability of them being zero is less
+     than any hardware failure.  Some specs however require it.  */
+  do
     {
-      while (!mpi_cmp_ui (r, 0)) /* r == 0 */
+      do
         {
-          /* Note, that we are guaranteed to enter this loop at least
-             once because r has been intialized to 0.  We can't use a
-             do_while because we want to keep the value of R even if S
-             has to be recomputed.  */
-
           mpi_free (k);
           k = NULL;
           if ((flags & PUBKEY_FLAG_RFC6979) && hashalgo)
@@ -458,11 +453,14 @@ sign_ecdsa (gcry_mpi_t input, ECC_secret_key *skey, gcry_mpi_t r, gcry_mpi_t s,
             }
           mpi_mod (r, x, skey->E.n);  /* r = x mod n */
         }
+      while (!mpi_cmp_ui (r, 0));
+
       mpi_mulm (dr, skey->d, r, skey->E.n); /* dr = d*r mod n  */
       mpi_addm (sum, hash, dr, skey->E.n);  /* sum = hash + (d*r) mod n  */
       mpi_invm (k_1, k, skey->E.n);         /* k_1 = k^(-1) mod n  */
       mpi_mulm (s, k_1, sum, skey->E.n);    /* s = k^(-1)*(hash+(d*r)) mod n */
     }
+  while (!mpi_cmp_ui (s, 0));
 
   if (DBG_CIPHER)
     {

-----------------------------------------------------------------------

Summary of changes:
 cipher/ecc.c |   18 ++++++++----------
 1 files changed, 8 insertions(+), 10 deletions(-)


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