Constant time DH [sync with mainstream].

Submitted by: bodo

diff --git a/fips/dh/fips_dh_key.c b/fips/dh/fips_dh_key.c
index 7d6f259b5062298fa245be0cc048ac98e08e72dd..581de173649ccde3e4526f72366c8b488d063522 100644 (file)
--- a/fips/dh/fips_dh_key.c
+++ b/fips/dh/fips_dh_key.c
@@ -145,8 +145,22 @@ static int generate_key(DH *dh)
                l = dh->length ? dh->length : BN_num_bits(dh->p)-1; /* secret exponent length */
                if (!BN_rand(priv_key, l, 0, 0)) goto err;
                }
-       if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, priv_key,dh->p,ctx,mont))
-               goto err;
+
+       {
+               BIGNUM local_prk;
+               BIGNUM *prk;
+
+               if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0)
+                       {
+                       prk = &local_prk;
+                       BN_with_flags(prk, priv_key, BN_FLG_EXP_CONSTTIME);
+                       }
+               else
+                       prk = priv_key;
+
+               if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont))
+                       goto err;
+       }
                
        dh->pub_key=pub_key;
        dh->priv_key=priv_key;
@@ -184,6 +198,11 @@ static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
                mont = BN_MONT_CTX_set_locked(
                                (BN_MONT_CTX **)&dh->method_mont_p,
                                CRYPTO_LOCK_DH, dh->p, ctx);
+               if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0)
+                       {
+                       /* XXX */
+                       BN_set_flags(dh->priv_key, BN_FLG_EXP_CONSTTIME);
+                       }
                if (!mont)
                        goto err;
                }
@@ -206,7 +225,10 @@ static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
                        const BIGNUM *m, BN_CTX *ctx,
                        BN_MONT_CTX *m_ctx)
        {
-       if (a->top == 1)
+       /* If a is only one word long and constant time is false, use the faster
+        * exponenentiation function.
+        */
+       if (a->top == 1 && ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) != 0))
                {
                BN_ULONG A = a->d[0];
                return BN_mod_exp_mont_word(r,A,p,m,ctx,m_ctx);