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security/openssl-chelsio/files/patch-CVE-2018-0734
- This file was added.
Property | Old Value | New Value |
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fbsd:nokeywords | null | yes \ No newline at end of property |
svn:eol-style | null | native \ No newline at end of property |
svn:mime-type | null | text/plain \ No newline at end of property |
Timing vulnerability in DSA signature generation (CVE-2018-0734). | |||||
Avoid a timing attack that leaks information via a side channel that | |||||
triggers when a BN is resized. Increasing the size of the BNs | |||||
prior to doing anything with them suppresses the attack. | |||||
Thanks due to Samuel Weiser for finding and locating this. | |||||
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de> | |||||
(Merged from #7486) | |||||
(cherry picked from commit a9cfb8c) | |||||
https://github.com/openssl/openssl/commit/8abfe72e8c1de1b95f50aa0d9134803b4d00070f | |||||
--- crypto/dsa/dsa_ossl.c.orig 2018-09-11 12:48:21 UTC | |||||
+++ crypto/dsa/dsa_ossl.c | |||||
@@ -9,6 +9,7 @@ | |||||
#include <stdio.h> | |||||
#include "internal/cryptlib.h" | |||||
+#include "internal/bn_int.h" | |||||
#include <openssl/bn.h> | |||||
#include <openssl/sha.h> | |||||
#include "dsa_locl.h" | |||||
@@ -178,9 +179,9 @@ static int dsa_sign_setup(DSA *dsa, BN_C | |||||
{ | |||||
BN_CTX *ctx = NULL; | |||||
BIGNUM *k, *kinv = NULL, *r = *rp; | |||||
- BIGNUM *l, *m; | |||||
+ BIGNUM *l; | |||||
int ret = 0; | |||||
- int q_bits; | |||||
+ int q_bits, q_words; | |||||
if (!dsa->p || !dsa->q || !dsa->g) { | |||||
DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS); | |||||
@@ -189,8 +190,7 @@ static int dsa_sign_setup(DSA *dsa, BN_C | |||||
k = BN_new(); | |||||
l = BN_new(); | |||||
- m = BN_new(); | |||||
- if (k == NULL || l == NULL || m == NULL) | |||||
+ if (k == NULL || l == NULL) | |||||
goto err; | |||||
if (ctx_in == NULL) { | |||||
@@ -201,9 +201,9 @@ static int dsa_sign_setup(DSA *dsa, BN_C | |||||
/* Preallocate space */ | |||||
q_bits = BN_num_bits(dsa->q); | |||||
- if (!BN_set_bit(k, q_bits) | |||||
- || !BN_set_bit(l, q_bits) | |||||
- || !BN_set_bit(m, q_bits)) | |||||
+ q_words = bn_get_top(dsa->q); | |||||
+ if (!bn_wexpand(k, q_words + 2) | |||||
+ || !bn_wexpand(l, q_words + 2)) | |||||
goto err; | |||||
/* Get random k */ | |||||
@@ -238,14 +238,17 @@ static int dsa_sign_setup(DSA *dsa, BN_C | |||||
* small timing information leakage. We then choose the sum that is | |||||
* one bit longer than the modulus. | |||||
* | |||||
- * TODO: revisit the BN_copy aiming for a memory access agnostic | |||||
- * conditional copy. | |||||
+ * There are some concerns about the efficacy of doing this. More | |||||
+ * specificly refer to the discussion starting with: | |||||
+ * https://github.com/openssl/openssl/pull/7486#discussion_r228323705 | |||||
+ * The fix is to rework BN so these gymnastics aren't required. | |||||
*/ | |||||
if (!BN_add(l, k, dsa->q) | |||||
- || !BN_add(m, l, dsa->q) | |||||
- || !BN_copy(k, BN_num_bits(l) > q_bits ? l : m)) | |||||
+ || !BN_add(k, l, dsa->q)) | |||||
goto err; | |||||
+ BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2); | |||||
+ | |||||
if ((dsa)->meth->bn_mod_exp != NULL) { | |||||
if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx, | |||||
dsa->method_mont_p)) | |||||
@@ -258,7 +261,7 @@ static int dsa_sign_setup(DSA *dsa, BN_C | |||||
if (!BN_mod(r, r, dsa->q, ctx)) | |||||
goto err; | |||||
- /* Compute part of 's = inv(k) (m + xr) mod q' */ | |||||
+ /* Compute part of 's = inv(k) (m + xr) mod q' */ | |||||
if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL) | |||||
goto err; | |||||
@@ -273,7 +276,6 @@ static int dsa_sign_setup(DSA *dsa, BN_C | |||||
BN_CTX_free(ctx); | |||||
BN_clear_free(k); | |||||
BN_clear_free(l); | |||||
- BN_clear_free(m); | |||||
return ret; | |||||
} | |||||