113 lines
3.6 KiB
Diff
113 lines
3.6 KiB
Diff
Fix CVE-2016-2178.
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<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2178>
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Source:
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<https://git.openssl.org/?p=openssl.git;a=commit;h=621eaf49a289bfac26d4cbcdb7396e796784c534>
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<https://git.openssl.org/?p=openssl.git;a=commit;h=b7d0f2834e139a20560d64c73e2565e93715ce2b>
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From 621eaf49a289bfac26d4cbcdb7396e796784c534 Mon Sep 17 00:00:00 2001
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From: Cesar Pereida <cesar.pereida@aalto.fi>
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Date: Mon, 23 May 2016 12:45:25 +0300
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Subject: [PATCH 1/2] Fix DSA, preserve BN_FLG_CONSTTIME
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Operations in the DSA signing algorithm should run in constant time in
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order to avoid side channel attacks. A flaw in the OpenSSL DSA
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implementation means that a non-constant time codepath is followed for
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certain operations. This has been demonstrated through a cache-timing
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attack to be sufficient for an attacker to recover the private DSA key.
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CVE-2016-2178
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Reviewed-by: Richard Levitte <levitte@openssl.org>
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Reviewed-by: Matt Caswell <matt@openssl.org>
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---
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crypto/dsa/dsa_ossl.c | 6 +++---
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1 file changed, 3 insertions(+), 3 deletions(-)
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diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c
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index efc4f1b..b29eb4b 100644
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--- a/crypto/dsa/dsa_ossl.c
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+++ b/crypto/dsa/dsa_ossl.c
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@@ -248,9 +248,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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if (!BN_rand_range(&k, dsa->q))
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goto err;
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while (BN_is_zero(&k)) ;
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- if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
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- BN_set_flags(&k, BN_FLG_CONSTTIME);
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- }
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if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
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if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
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@@ -279,9 +276,12 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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}
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K = &kq;
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+
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+ BN_set_flags(K, BN_FLG_CONSTTIME);
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} else {
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K = &k;
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}
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+
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DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, K, dsa->p, ctx,
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dsa->method_mont_p);
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if (!BN_mod(r, r, dsa->q, ctx))
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--
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2.8.4
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From b7d0f2834e139a20560d64c73e2565e93715ce2b Mon Sep 17 00:00:00 2001
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From: Matt Caswell <matt@openssl.org>
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Date: Tue, 7 Jun 2016 09:12:51 +0100
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Subject: [PATCH 2/2] More fix DSA, preserve BN_FLG_CONSTTIME
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The previous "fix" still left "k" exposed to constant time problems in
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the later BN_mod_inverse() call. Ensure both k and kq have the
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BN_FLG_CONSTTIME flag set at the earliest opportunity after creation.
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CVE-2016-2178
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Reviewed-by: Rich Salz <rsalz@openssl.org>
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---
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crypto/dsa/dsa_ossl.c | 11 ++++++++---
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1 file changed, 8 insertions(+), 3 deletions(-)
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diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c
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index b29eb4b..58013a4 100644
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--- a/crypto/dsa/dsa_ossl.c
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+++ b/crypto/dsa/dsa_ossl.c
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@@ -247,7 +247,12 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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do
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if (!BN_rand_range(&k, dsa->q))
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goto err;
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- while (BN_is_zero(&k)) ;
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+ while (BN_is_zero(&k));
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+
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+ if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
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+ BN_set_flags(&k, BN_FLG_CONSTTIME);
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+ }
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+
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if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
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if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
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@@ -261,6 +266,8 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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if (!BN_copy(&kq, &k))
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goto err;
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+ BN_set_flags(&kq, BN_FLG_CONSTTIME);
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+
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/*
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* We do not want timing information to leak the length of k, so we
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* compute g^k using an equivalent exponent of fixed length. (This
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@@ -276,8 +283,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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}
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K = &kq;
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-
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- BN_set_flags(K, BN_FLG_CONSTTIME);
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} else {
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K = &k;
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}
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--
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2.8.4
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