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 11:08:15 +0100 |
| commit | 399944622df7bd81af62e67ea967c470534090e2 (patch) | |
| tree | 6d779ba9bc1e291a82fe1cb5a460ede441634fdb /crypto/dsa | |
| parent | 0a4c87a90c6cf6628c688868cd5f13e4b9a5f19d (diff) | |
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>
Diffstat (limited to 'crypto/dsa')
| -rw-r--r-- | crypto/dsa/dsa_ossl.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c index ce1da1cd6f..beb62b2ff0 100644 --- a/crypto/dsa/dsa_ossl.c +++ b/crypto/dsa/dsa_ossl.c @@ -204,10 +204,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, 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, dsa->lock, dsa->p, ctx)) @@ -238,6 +234,11 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, } else { K = k; } + + if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) { + BN_set_flags(K, BN_FLG_CONSTTIME); + } + 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)) |