1 files changed, 15 insertions, 1 deletions

diff --git a/src/lib/libcrypto/dsa/dsa_ossl.c b/src/lib/libcrypto/dsa/dsa_ossl.c
index a3ddd7d281..b3d78e524c 100644
--- a/src/lib/libcrypto/dsa/dsa_ossl.c
+++ b/src/lib/libcrypto/dsa/dsa_ossl.c
@@ -136,6 +136,7 @@ static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
         BN_CTX *ctx=NULL;
         int reason=ERR_R_BN_LIB;
         DSA_SIG *ret=NULL;
+        int noredo = 0;
 
         BN_init(&m);
         BN_init(&xr);
@@ -150,7 +151,7 @@ static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
         if (s == NULL) goto err;
         ctx=BN_CTX_new();
         if (ctx == NULL) goto err;
-
+redo:
         if ((dsa->kinv == NULL) || (dsa->r == NULL))
                 {
                 if (!DSA_sign_setup(dsa,ctx,&kinv,&r)) goto err;
@@ -161,6 +162,7 @@ static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
                 dsa->kinv=NULL;
                 r=dsa->r;
                 dsa->r=NULL;
+                noredo = 1;
                 }
 
         
@@ -181,6 +183,18 @@ static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
 
         ret=DSA_SIG_new();
         if (ret == NULL) goto err;
+        /* Redo if r or s is zero as required by FIPS 186-3: this is
+         * very unlikely.
+         */
+        if (BN_is_zero(r) || BN_is_zero(s))
+                {
+                if (noredo)
+                        {
+                        reason = DSA_R_NEED_NEW_SETUP_VALUES;
+                        goto err;
+                        }
+                goto redo;
+                }
         ret->r = r;
         ret->s = s;