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deps: float two (more) OpenSSL patches for DSA vulnerabilities #23965

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deps: float two (more) OpenSSL patches for DSA vulnerabilities #23965

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f9c336d
deps: float 415c3356 from openssl (DSA vulnerability)
rvagg Oct 30, 2018
082e301
deps: float a9cfb8c2 from openssl (CVE-2018-0734)
rvagg Oct 30, 2018
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60 changes: 46 additions & 14 deletions deps/openssl/openssl/crypto/dsa/dsa_ossl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@

#include <stdio.h>
#include "internal/cryptlib.h"
#include "internal/bn_int.h"
#include <openssl/bn.h>
#include <openssl/sha.h>
#include "dsa_locl.h"
Expand All @@ -25,6 +26,8 @@ static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
DSA_SIG *sig, DSA *dsa);
static int dsa_init(DSA *dsa);
static int dsa_finish(DSA *dsa);
static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
BN_CTX *ctx);

static DSA_METHOD openssl_dsa_meth = {
"OpenSSL DSA method",
Expand Down Expand Up @@ -180,9 +183,9 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
{
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);
Expand All @@ -191,8 +194,7 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,

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) {
Expand All @@ -203,9 +205,9 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,

/* 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 */
Expand Down Expand Up @@ -240,14 +242,17 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
* 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))
Expand All @@ -260,8 +265,8 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
if (!BN_mod(r, r, dsa->q, ctx))
goto err;

/* Compute part of 's = inv(k) (m + xr) mod q' */
if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL)
/* Compute part of 's = inv(k) (m + xr) mod q' */
if ((kinv = dsa_mod_inverse_fermat(k, dsa->q, ctx)) == NULL)
goto err;

BN_clear_free(*kinvp);
Expand All @@ -275,7 +280,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
BN_CTX_free(ctx);
BN_clear_free(k);
BN_clear_free(l);
BN_clear_free(m);
return ret;
}

Expand Down Expand Up @@ -395,3 +399,31 @@ static int dsa_finish(DSA *dsa)
BN_MONT_CTX_free(dsa->method_mont_p);
return (1);
}

/*
* Compute the inverse of k modulo q.
* Since q is prime, Fermat's Little Theorem applies, which reduces this to
* mod-exp operation. Both the exponent and modulus are public information
* so a mod-exp that doesn't leak the base is sufficient. A newly allocated
* BIGNUM is returned which the caller must free.
*/
static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
BN_CTX *ctx)
{
BIGNUM *res = NULL;
BIGNUM *r, *e;

if ((r = BN_new()) == NULL)
return NULL;

BN_CTX_start(ctx);
if ((e = BN_CTX_get(ctx)) != NULL
&& BN_set_word(r, 2)
&& BN_sub(e, q, r)
&& BN_mod_exp_mont(r, k, e, q, ctx, NULL))
res = r;
else
BN_free(r);
BN_CTX_end(ctx);
return res;
}