Check for invalid keys, with even p, in dsa_sign.

ChangeLog

 2016-08-04  Niels Möller  <nisse@lysator.liu.se>
 
+	* dsa-sign.c (dsa_sign): Return failure if p is even, so that an
+	invalid key doesn't result in a crash inside mpz_powm_sec.
+
 	* rsa-sign-tr.c (rsa_compute_root_tr): Return failure if any of p,
 	q or n is even, to avoid crashing inside mpz_powm_sec. Invalid
 	keys with even modulo are rejected by rsa_public_key_prepare and

dsa-sign.c

@@ -56,6 +56,11 @@ dsa_sign(const struct dsa_params *params,
   mpz_t tmp;
   int res;
   
+  /* Check that p is odd, so that invalid keys don't result in a crash
+     inside mpz_powm_sec. */
+  if (mpz_even_p (params->p))
+    return 0;
+
   /* Select k, 0<k<q, randomly */
   mpz_init_set(tmp, params->q);
   mpz_sub_ui(tmp, tmp, 1);