From 3681a4558c13198944e6f7f149c4be188e076e14 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Tue, 7 Jun 2016 09:12:51 +0100 Subject: More fix DSA, preserve BN_FLG_CONSTTIME The previous "fix" still left "k" exposed to constant time problems in the later BN_mod_inverse() call. Ensure both k and kq have the BN_FLG_CONSTTIME flag set at the earliest opportunity after creation. CVE-2016-2178 Reviewed-by: Rich Salz (cherry picked from commit b7d0f2834e139a20560d64c73e2565e93715ce2b) --- crypto/dsa/dsa_ossl.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c index 01e3d74af1..06cd2a2aed 100644 --- a/crypto/dsa/dsa_ossl.c +++ b/crypto/dsa/dsa_ossl.c @@ -247,7 +247,12 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, do if (!BN_rand_range(&k, dsa->q)) goto err; - while (BN_is_zero(&k)) ; + 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, @@ -261,6 +266,8 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, if (!BN_copy(&kq, &k)) goto err; + BN_set_flags(&kq, BN_FLG_CONSTTIME); + /* * 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 @@ -276,8 +283,6 @@ 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; } -- cgit v1.2.3