diff options
| author | Cesar Pereida <cesar.pereida@aalto.fi> | 2016-05-23 12:45:25 +0300 |
|---|---|---|
| committer | Matt Caswell <matt@openssl.org> | 2016-06-06 11:27:55 +0100 |
| commit | 621eaf49a289bfac26d4cbcdb7396e796784c534 (patch) | |
| tree | d909d0808687d7b6d711acce768272529ad8233f | |
| parent | 46bad91986eb56f2beb9059e14fb4ee94c3f952a (diff) | |
| download | openssl-621eaf49a289bfac26d4cbcdb7396e796784c534.tar.gz | |
Fix DSA, preserve BN_FLG_CONSTTIME
Operations in the DSA signing algorithm should run in constant time in
order to avoid side channel attacks. A flaw in the OpenSSL DSA
implementation means that a non-constant time codepath is followed for
certain operations. This has been demonstrated through a cache-timing
attack to be sufficient for an attacker to recover the private DSA key.
CVE-2016-2178
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
| -rw-r--r-- | crypto/dsa/dsa_ossl.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c index efc4f1b6ae..b29eb4bc51 100644 --- a/crypto/dsa/dsa_ossl.c +++ b/crypto/dsa/dsa_ossl.c @@ -248,9 +248,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 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_CONSTTIME); - } if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p, @@ -279,9 +276,12 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, } K = &kq; + + BN_set_flags(K, BN_FLG_CONSTTIME); } else { K = &k; } + DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, K, dsa->p, ctx, dsa->method_mont_p); if (!BN_mod(r, r, dsa->q, ctx)) |