File gnutls-CVE-2024-28834.patch of Package gnutls.37572
From 1c4701ffc342259fc5965d5a0de90d87f780e3e5 Mon Sep 17 00:00:00 2001
From: Daiki Ueno <ueno@gnu.org>
Date: Fri, 12 Jan 2024 17:56:58 +0900
Subject: [PATCH] nettle: avoid normalization of mpz_t in deterministic ECDSA
This removes function calls that potentially leak bit-length of a
private key used to calculate a nonce in deterministic ECDSA. Namely:
- _gnutls_dsa_compute_k has been rewritten to work on always
zero-padded mp_limb_t arrays instead of mpz_t
- rnd_mpz_func has been replaced with rnd_datum_func, which is backed
by a byte array instead of an mpz_t value
Signed-off-by: Daiki Ueno <ueno@gnu.org>
---
lib/nettle/int/dsa-compute-k.c | 70 +++++++++++++++++++++----------
lib/nettle/int/dsa-compute-k.h | 23 +++++++++-
lib/nettle/int/ecdsa-compute-k.c | 28 +++----------
lib/nettle/int/ecdsa-compute-k.h | 4 +-
lib/nettle/pk.c | 65 +++++++++++++++++++++-------
tests/sign-verify-deterministic.c | 2 +-
6 files changed, 127 insertions(+), 65 deletions(-)
Index: gnutls-3.7.3/lib/nettle/int/dsa-compute-k.c
===================================================================
--- gnutls-3.7.3.orig/lib/nettle/int/dsa-compute-k.c
+++ gnutls-3.7.3/lib/nettle/int/dsa-compute-k.c
@@ -31,33 +31,37 @@
#include "mpn-base256.h"
#include <string.h>
-#define BITS_TO_LIMBS(bits) (((bits) + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS)
+/* For mini-gmp */
+#ifndef GMP_LIMB_BITS
+#define GMP_LIMB_BITS GMP_NUMB_BITS
+#endif
+
+static inline int is_zero_limb(mp_limb_t x)
+{
+ x |= (x << 1);
+ return ((x >> 1) - 1) >> (GMP_LIMB_BITS - 1);
+}
+
+static int sec_zero_p(const mp_limb_t *ap, mp_size_t n)
+{
+ volatile mp_limb_t w;
+ mp_size_t i;
+
+ for (i = 0, w = 0; i < n; i++)
+ w |= ap[i];
-/* The maximum size of q, choosen from the fact that we support
- * 521-bit elliptic curve generator and 512-bit DSA subgroup at
- * maximum. */
-#define MAX_Q_BITS 521
-#define MAX_Q_SIZE ((MAX_Q_BITS + 7) / 8)
-#define MAX_Q_LIMBS BITS_TO_LIMBS(MAX_Q_BITS)
-
-#define MAX_HASH_BITS (MAX_HASH_SIZE * 8)
-#define MAX_HASH_LIMBS BITS_TO_LIMBS(MAX_HASH_BITS)
-
-int
-_gnutls_dsa_compute_k(mpz_t k,
- const mpz_t q,
- const mpz_t x,
- gnutls_mac_algorithm_t mac,
- const uint8_t *digest,
- size_t length)
+ return is_zero_limb(w);
+}
+
+int _gnutls_dsa_compute_k(mp_limb_t *h, const mp_limb_t *q, const mp_limb_t *x,
+ mp_size_t qn, mp_bitcnt_t q_bits,
+ gnutls_mac_algorithm_t mac, const uint8_t *digest,
+ size_t length)
{
uint8_t V[MAX_HASH_SIZE];
uint8_t K[MAX_HASH_SIZE];
uint8_t xp[MAX_Q_SIZE];
uint8_t tp[MAX_Q_SIZE];
- mp_limb_t h[MAX(MAX_Q_LIMBS, MAX_HASH_LIMBS)];
- mp_bitcnt_t q_bits = mpz_sizeinbase (q, 2);
- mp_size_t qn = mpz_size(q);
mp_bitcnt_t h_bits = length * 8;
mp_size_t hn = BITS_TO_LIMBS(h_bits);
size_t nbytes = (q_bits + 7) / 8;
@@ -66,6 +70,7 @@ _gnutls_dsa_compute_k(mpz_t k,
mp_limb_t cy;
gnutls_hmac_hd_t hd;
int ret = 0;
+ mp_limb_t scratch[MAX_Q_LIMBS];
if (unlikely(q_bits > MAX_Q_BITS))
return gnutls_assert_val(GNUTLS_E_INVALID_REQUEST);
@@ -73,7 +78,7 @@ _gnutls_dsa_compute_k(mpz_t k,
return gnutls_assert_val(GNUTLS_E_INVALID_REQUEST);
/* int2octets(x) */
- mpn_get_base256(xp, nbytes, mpz_limbs_read(x), qn);
+ mpn_get_base256(xp, nbytes, x, qn);
/* bits2octets(h) */
mpn_set_base256(h, hn, digest, length);
@@ -97,12 +102,12 @@ _gnutls_dsa_compute_k(mpz_t k,
mpn_rshift(h, h, hn, shift % GMP_NUMB_BITS);
}
- cy = mpn_sub_n(h, h, mpz_limbs_read(q), qn);
+ cy = mpn_sub_n(h, h, q, qn);
/* Fall back to addmul_1, if nettle is linked with mini-gmp. */
#ifdef mpn_cnd_add_n
- mpn_cnd_add_n(cy, h, h, mpz_limbs_read(q), qn);
+ mpn_cnd_add_n(cy, h, h, q, qn);
#else
- mpn_addmul_1(h, mpz_limbs_read(q), qn, cy != 0);
+ mpn_addmul_1(h, q, qn, cy != 0);
#endif
mpn_get_base256(tp, nbytes, h, qn);
@@ -178,12 +183,8 @@ _gnutls_dsa_compute_k(mpz_t k,
if (tlen * 8 > q_bits)
mpn_rshift (h, h, qn, tlen * 8 - q_bits);
/* Check if k is in [1,q-1] */
- if (!mpn_zero_p (h, qn) &&
- mpn_cmp (h, mpz_limbs_read(q), qn) < 0) {
- mpn_copyi(mpz_limbs_write(k, qn), h, qn);
- mpz_limbs_finish(k, qn);
+ if (!sec_zero_p(h, qn) && mpn_sub_n(scratch, h, q, qn))
break;
- }
ret = gnutls_hmac_init(&hd, mac, K, length);
if (ret < 0)
@@ -207,3 +208,24 @@ _gnutls_dsa_compute_k(mpz_t k,
return ret;
}
+
+/* cancel-out dsa_sign's addition of 1 to random data */
+void _gnutls_dsa_compute_k_finish(uint8_t *k, size_t nbytes, mp_limb_t *h,
+ mp_size_t n)
+{
+ /* Fall back to sub_1, if nettle is linked with mini-gmp. */
+#ifdef mpn_sec_sub_1
+ mp_limb_t t[MAX_Q_LIMBS];
+
+ mpn_sec_sub_1(h, h, n, 1, t);
+#else
+ mpn_sub_1(h, h, n, 1);
+#endif
+ mpn_get_base256(k, nbytes, h, n);
+}
+
+void _gnutls_ecdsa_compute_k_finish(uint8_t *k, size_t nbytes, mp_limb_t *h,
+ mp_size_t n)
+{
+ mpn_get_base256(k, nbytes, h, n);
+}
Index: gnutls-3.7.3/lib/nettle/int/dsa-compute-k.h
===================================================================
--- gnutls-3.7.3.orig/lib/nettle/int/dsa-compute-k.h
+++ gnutls-3.7.3/lib/nettle/int/dsa-compute-k.h
@@ -26,12 +26,29 @@
#include <gnutls/gnutls.h>
#include <nettle/bignum.h> /* includes gmp.h */
-int
-_gnutls_dsa_compute_k(mpz_t k,
- const mpz_t q,
- const mpz_t x,
- gnutls_mac_algorithm_t mac,
- const uint8_t *digest,
- size_t length);
+#define BITS_TO_LIMBS(bits) (((bits) + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS)
+
+/* The maximum size of q, chosen from the fact that we support
+ * 521-bit elliptic curve generator and 512-bit DSA subgroup at
+ * maximum. */
+#define MAX_Q_BITS 521
+#define MAX_Q_SIZE ((MAX_Q_BITS + 7) / 8)
+#define MAX_Q_LIMBS BITS_TO_LIMBS(MAX_Q_BITS)
+
+#define MAX_HASH_BITS (MAX_HASH_SIZE * 8)
+#define MAX_HASH_LIMBS BITS_TO_LIMBS(MAX_HASH_BITS)
+
+#define DSA_COMPUTE_K_ITCH MAX(MAX_Q_LIMBS, MAX_HASH_LIMBS)
+
+int _gnutls_dsa_compute_k(mp_limb_t *h, const mp_limb_t *q, const mp_limb_t *x,
+ mp_size_t qn, mp_bitcnt_t q_bits,
+ gnutls_mac_algorithm_t mac, const uint8_t *digest,
+ size_t length);
+
+void _gnutls_dsa_compute_k_finish(uint8_t *k, size_t nbytes, mp_limb_t *h,
+ mp_size_t n);
+
+void _gnutls_ecdsa_compute_k_finish(uint8_t *k, size_t nbytes, mp_limb_t *h,
+ mp_size_t n);
#endif /* GNUTLS_LIB_NETTLE_INT_DSA_COMPUTE_K_H */
Index: gnutls-3.7.3/lib/nettle/int/ecdsa-compute-k.c
===================================================================
--- gnutls-3.7.3.orig/lib/nettle/int/ecdsa-compute-k.c
+++ gnutls-3.7.3/lib/nettle/int/ecdsa-compute-k.c
@@ -29,39 +29,38 @@
#include "dsa-compute-k.h"
#include "gnutls_int.h"
-static inline int
-_gnutls_ecc_curve_to_dsa_q(mpz_t *q, gnutls_ecc_curve_t curve)
+int _gnutls_ecc_curve_to_dsa_q(mpz_t q, gnutls_ecc_curve_t curve)
{
switch (curve) {
#ifdef ENABLE_NON_SUITEB_CURVES
case GNUTLS_ECC_CURVE_SECP192R1:
- mpz_init_set_str(*q,
+ mpz_init_set_str(q,
"FFFFFFFFFFFFFFFFFFFFFFFF99DEF836"
"146BC9B1B4D22831",
16);
return 0;
case GNUTLS_ECC_CURVE_SECP224R1:
- mpz_init_set_str(*q,
+ mpz_init_set_str(q,
"FFFFFFFFFFFFFFFFFFFFFFFFFFFF16A2"
"E0B8F03E13DD29455C5C2A3D",
16);
return 0;
#endif
case GNUTLS_ECC_CURVE_SECP256R1:
- mpz_init_set_str(*q,
+ mpz_init_set_str(q,
"FFFFFFFF00000000FFFFFFFFFFFFFFFF"
"BCE6FAADA7179E84F3B9CAC2FC632551",
16);
return 0;
case GNUTLS_ECC_CURVE_SECP384R1:
- mpz_init_set_str(*q,
+ mpz_init_set_str(q,
"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
"FFFFFFFFFFFFFFFFC7634D81F4372DDF"
"581A0DB248B0A77AECEC196ACCC52973",
16);
return 0;
case GNUTLS_ECC_CURVE_SECP521R1:
- mpz_init_set_str(*q,
+ mpz_init_set_str(q,
"1FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
"FFA51868783BF2F966B7FCC0148F709A"
@@ -73,23 +72,3 @@ _gnutls_ecc_curve_to_dsa_q(mpz_t *q, gnu
return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_SIGNATURE_ALGORITHM);
}
}
-
-int
-_gnutls_ecdsa_compute_k (mpz_t k,
- gnutls_ecc_curve_t curve,
- const mpz_t x,
- gnutls_mac_algorithm_t mac,
- const uint8_t *digest,
- size_t length)
-{
- mpz_t q;
- int ret;
-
- ret = _gnutls_ecc_curve_to_dsa_q(&q, curve);
- if (ret < 0)
- return gnutls_assert_val(ret);
-
- ret = _gnutls_dsa_compute_k (k, q, x, mac, digest, length);
- mpz_clear(q);
- return ret;
-}
Index: gnutls-3.7.3/lib/nettle/int/ecdsa-compute-k.h
===================================================================
--- gnutls-3.7.3.orig/lib/nettle/int/ecdsa-compute-k.h
+++ gnutls-3.7.3/lib/nettle/int/ecdsa-compute-k.h
@@ -26,12 +26,6 @@
#include <gnutls/gnutls.h>
#include <nettle/bignum.h> /* includes gmp.h */
-int
-_gnutls_ecdsa_compute_k (mpz_t k,
- gnutls_ecc_curve_t curve,
- const mpz_t x,
- gnutls_mac_algorithm_t mac,
- const uint8_t *digest,
- size_t length);
+int _gnutls_ecc_curve_to_dsa_q(mpz_t q, gnutls_ecc_curve_t curve);
#endif /* GNUTLS_LIB_NETTLE_INT_ECDSA_COMPUTE_K_H */
Index: gnutls-3.7.3/lib/nettle/pk.c
===================================================================
--- gnutls-3.7.3.orig/lib/nettle/pk.c
+++ gnutls-3.7.3/lib/nettle/pk.c
@@ -100,10 +100,16 @@ static void rnd_nonce_func(void *_ctx, s
}
}
-static void rnd_mpz_func(void *_ctx, size_t length, uint8_t * data)
+static void rnd_datum_func(void *ctx, size_t length, uint8_t * data)
{
- mpz_t *k = _ctx;
- nettle_mpz_get_str_256 (length, data, *k);
+ gnutls_datum_t *d = ctx;
+
+ if (length > d->size) {
+ memset(data, 0, length - d->size);
+ memcpy(data + (length - d->size), d->data, d->size);
+ } else {
+ memcpy(data, d->data, length);
+ }
}
static void rnd_nonce_func_fallback(void *_ctx, size_t length, uint8_t * data)
@@ -1184,7 +1190,10 @@ _wrap_nettle_pk_sign(gnutls_pk_algorithm
struct dsa_signature sig;
int curve_id = pk_params->curve;
const struct ecc_curve *curve;
- mpz_t k;
+ mpz_t q;
+ /* 521-bit elliptic curve generator at maximum */
+ uint8_t buf[(521 + 7) / 8];
+ gnutls_datum_t k = { NULL, 0 };
void *random_ctx;
nettle_random_func *random_func;
@@ -1231,19 +1240,31 @@ _wrap_nettle_pk_sign(gnutls_pk_algorithm
hash_len = vdata->size;
}
- mpz_init(k);
+ mpz_init(q);
if (_gnutls_get_lib_state() == LIB_STATE_SELFTEST ||
(sign_params->flags & GNUTLS_PK_FLAG_REPRODUCIBLE)) {
- ret = _gnutls_ecdsa_compute_k(k,
- curve_id,
- pk_params->params[ECC_K],
- DIG_TO_MAC(sign_params->dsa_dig),
- vdata->data,
- vdata->size);
+ mp_limb_t h[DSA_COMPUTE_K_ITCH];
+
+ ret = _gnutls_ecc_curve_to_dsa_q(q, curve_id);
+ if (ret < 0)
+ goto ecdsa_cleanup;
+
+ ret = _gnutls_dsa_compute_k(
+ h, mpz_limbs_read(q), priv.p,
+ ecc_size(priv.ecc), ecc_bit_size(priv.ecc),
+ DIG_TO_MAC(sign_params->dsa_dig), vdata->data,
+ vdata->size);
if (ret < 0)
goto ecdsa_cleanup;
+
+ k.data = buf;
+ k.size = (ecc_bit_size(priv.ecc) + 7) / 8;
+
+ _gnutls_ecdsa_compute_k_finish(k.data, k.size, h,
+ ecc_size(priv.ecc));
+
random_ctx = &k;
- random_func = rnd_mpz_func;
+ random_func = rnd_datum_func;
} else {
random_ctx = NULL;
random_func = rnd_nonce_func;
@@ -1264,7 +1285,7 @@ _wrap_nettle_pk_sign(gnutls_pk_algorithm
ecdsa_cleanup:
dsa_signature_clear(&sig);
ecc_scalar_zclear(&priv);
- mpz_clear(k);
+ mpz_clear(q);
if (ret < 0) {
gnutls_assert();
@@ -1277,7 +1298,9 @@ _wrap_nettle_pk_sign(gnutls_pk_algorithm
struct dsa_params pub;
bigint_t priv;
struct dsa_signature sig;
- mpz_t k;
+ /* 512-bit DSA subgroup at maximum */
+ uint8_t buf[(512 + 7) / 8];
+ gnutls_datum_t k = { NULL, 0 };
void *random_ctx;
nettle_random_func *random_func;
@@ -1304,21 +1327,27 @@ _wrap_nettle_pk_sign(gnutls_pk_algorithm
hash_len = vdata->size;
}
- mpz_init(k);
if (_gnutls_get_lib_state() == LIB_STATE_SELFTEST ||
(sign_params->flags & GNUTLS_PK_FLAG_REPRODUCIBLE)) {
- ret = _gnutls_dsa_compute_k(k,
- pub.q,
- TOMPZ(priv),
- DIG_TO_MAC(sign_params->dsa_dig),
- vdata->data,
+ mp_limb_t h[DSA_COMPUTE_K_ITCH];
+
+ ret = _gnutls_dsa_compute_k(
+ h, mpz_limbs_read(pub.q),
+ mpz_limbs_read(TOMPZ(priv)), mpz_size(pub.q),
+ mpz_sizeinbase(pub.q, 2),
+ DIG_TO_MAC(sign_params->dsa_dig), vdata->data,
vdata->size);
if (ret < 0)
goto dsa_fail;
- /* cancel-out dsa_sign's addition of 1 to random data */
- mpz_sub_ui (k, k, 1);
+
+ k.data = buf;
+ k.size = (mpz_sizeinbase(pub.q, 2) + 7) / 8;
+
+ _gnutls_dsa_compute_k_finish(k.data, k.size, h,
+ mpz_size(pub.q));
+
random_ctx = &k;
- random_func = rnd_mpz_func;
+ random_func = rnd_datum_func;
} else {
random_ctx = NULL;
random_func = rnd_nonce_func;
@@ -1338,7 +1367,6 @@ _wrap_nettle_pk_sign(gnutls_pk_algorithm
dsa_fail:
dsa_signature_clear(&sig);
- mpz_clear(k);
if (ret < 0) {
gnutls_assert();
Index: gnutls-3.7.3/tests/sign-verify-deterministic.c
===================================================================
--- gnutls-3.7.3.orig/tests/sign-verify-deterministic.c
+++ gnutls-3.7.3/tests/sign-verify-deterministic.c
@@ -197,7 +197,7 @@ void doit(void)
&signature);
if (ret < 0)
testfail("gnutls_pubkey_verify_data2\n");
- success(" - pass");
+ success(" - pass\n");
next:
gnutls_free(signature.data);
