1 files changed, 43 insertions, 12 deletions

diff --git a/src/lib/libcrypto/dsa/dsa_ossl.c b/src/lib/libcrypto/dsa/dsa_ossl.c
index f1a85afcde..12509a7083 100644
--- a/src/lib/libcrypto/dsa/dsa_ossl.c
+++ b/src/lib/libcrypto/dsa/dsa_ossl.c
@@ -172,7 +172,7 @@ err:
 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
         {
         BN_CTX *ctx;
-        BIGNUM k,*kinv=NULL,*r=NULL;
+        BIGNUM k,kq,*K,*kinv=NULL,*r=NULL;
         int ret=0;
 
         if (!dsa->p || !dsa->q || !dsa->g)
@@ -182,6 +182,7 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
                 }
 
         BN_init(&k);
+        BN_init(&kq);
 
         if (ctx_in == NULL)
                 {
@@ -191,22 +192,49 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
                 ctx=ctx_in;
 
         if ((r=BN_new()) == NULL) goto err;
-        kinv=NULL;
 
         /* Get random k */
         do
                 if (!BN_rand_range(&k, dsa->q)) goto err;
         while (BN_is_zero(&k));
+        if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0)
+                {
+                BN_set_flags(&k, BN_FLG_EXP_CONSTTIME);
+                }
 
-        if ((dsa->method_mont_p == NULL) && (dsa->flags & DSA_FLAG_CACHE_MONT_P))
+        if (dsa->flags & DSA_FLAG_CACHE_MONT_P)
                 {
-                if ((dsa->method_mont_p=(char *)BN_MONT_CTX_new()) != NULL)
-                        if (!BN_MONT_CTX_set((BN_MONT_CTX *)dsa->method_mont_p,
-                                dsa->p,ctx)) goto err;
+                if (!BN_MONT_CTX_set_locked((BN_MONT_CTX **)&dsa->method_mont_p,
+                                                CRYPTO_LOCK_DSA,
+                                                dsa->p, ctx))
+                        goto err;
                 }
 
         /* Compute r = (g^k mod p) mod q */
-        if (!dsa->meth->bn_mod_exp(dsa, r,dsa->g,&k,dsa->p,ctx,
+
+        if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0)
+                {
+                if (!BN_copy(&kq, &k)) goto err;
+
+                /* We do not want timing information to leak the length of k,
+                 * so we compute g^k using an equivalent exponent of fixed length.
+                 *
+                 * (This is a kludge that we need because the BN_mod_exp_mont()
+                 * does not let us specify the desired timing behaviour.) */
+
+                if (!BN_add(&kq, &kq, dsa->q)) goto err;
+                if (BN_num_bits(&kq) <= BN_num_bits(dsa->q))
+                        {
+                        if (!BN_add(&kq, &kq, dsa->q)) goto err;
+                        }
+
+                K = &kq;
+                }
+        else
+                {
+                K = &k;
+                }
+        if (!dsa->meth->bn_mod_exp(dsa, r,dsa->g,K,dsa->p,ctx,
                 (BN_MONT_CTX *)dsa->method_mont_p)) goto err;
         if (!BN_mod(r,r,dsa->q,ctx)) goto err;
 
@@ -229,6 +257,7 @@ err:
         if (ctx_in == NULL) BN_CTX_free(ctx);
         if (kinv != NULL) BN_clear_free(kinv);
         BN_clear_free(&k);
+        BN_clear_free(&kq);
         return(ret);
         }
 
@@ -275,13 +304,15 @@ static int dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig,
         /* u2 = r * w mod q */
         if (!BN_mod_mul(&u2,sig->r,&u2,dsa->q,ctx)) goto err;
 
-        if ((dsa->method_mont_p == NULL) && (dsa->flags & DSA_FLAG_CACHE_MONT_P))
+
+        if (dsa->flags & DSA_FLAG_CACHE_MONT_P)
                 {
-                if ((dsa->method_mont_p=(char *)BN_MONT_CTX_new()) != NULL)
-                        if (!BN_MONT_CTX_set((BN_MONT_CTX *)dsa->method_mont_p,
-                                dsa->p,ctx)) goto err;
+                mont = BN_MONT_CTX_set_locked(
+                                        (BN_MONT_CTX **)&dsa->method_mont_p,
+                                        CRYPTO_LOCK_DSA, dsa->p, ctx);
+                if (!mont)
+                        goto err;
                 }
-        mont=(BN_MONT_CTX *)dsa->method_mont_p;
 
 #if 0
         {