[openwrt/openwrt] hostapd: Apply SAE/EAP-pwd side-channel attack update 2
LEDE Commits
lede-commits at lists.infradead.org
Sun Feb 13 14:39:11 PST 2022
hauke pushed a commit to openwrt/openwrt.git, branch openwrt-19.07:
https://git.openwrt.org/e7596ce0b08595083a32870cc019de9bb514aaec
commit e7596ce0b08595083a32870cc019de9bb514aaec
Author: Hauke Mehrtens <hauke at hauke-m.de>
AuthorDate: Sat Feb 12 20:37:12 2022 +0100
hostapd: Apply SAE/EAP-pwd side-channel attack update 2
This fixes some recent security problems in hostapd.
See here for details: https://w1.fi/security/2022-1
* CVE-2022-23303
* CVE-2022-23304
Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
---
package/network/services/hostapd/Makefile | 2 +-
...rypto-Add-more-bignum-EC-helper-functions.patch | 309 +++++++++++++++++++++
.../082-dragonfly-Add-sqrt-helper-function.patch | 65 +++++
...the-y-coordinate-for-PWE-with-own-impleme.patch | 94 +++++++
...ive-the-y-coordinate-for-PWE-with-own-imp.patch | 108 +++++++
5 files changed, 577 insertions(+), 1 deletion(-)
diff --git a/package/network/services/hostapd/Makefile b/package/network/services/hostapd/Makefile
index 75615efd9b..4b41168cd5 100644
--- a/package/network/services/hostapd/Makefile
+++ b/package/network/services/hostapd/Makefile
@@ -7,7 +7,7 @@
include $(TOPDIR)/rules.mk
PKG_NAME:=hostapd
-PKG_RELEASE:=7
+PKG_RELEASE:=8
PKG_SOURCE_URL:=http://w1.fi/hostap.git
PKG_SOURCE_PROTO:=git
diff --git a/package/network/services/hostapd/patches/081-crypto-Add-more-bignum-EC-helper-functions.patch b/package/network/services/hostapd/patches/081-crypto-Add-more-bignum-EC-helper-functions.patch
new file mode 100644
index 0000000000..e83c5e60f2
--- /dev/null
+++ b/package/network/services/hostapd/patches/081-crypto-Add-more-bignum-EC-helper-functions.patch
@@ -0,0 +1,309 @@
+From 208e5687ff2e48622e28d8888ce5444a54353bbd Mon Sep 17 00:00:00 2001
+From: Jouni Malinen <jouni at codeaurora.org>
+Date: Tue, 27 Aug 2019 16:33:15 +0300
+Subject: [PATCH 1/4] crypto: Add more bignum/EC helper functions
+
+These are needed for implementing SAE hash-to-element.
+
+Signed-off-by: Jouni Malinen <jouni at codeaurora.org>
+---
+ src/crypto/crypto.h | 45 ++++++++++++++++++
+ src/crypto/crypto_openssl.c | 94 +++++++++++++++++++++++++++++++++++++
+ src/crypto/crypto_wolfssl.c | 66 ++++++++++++++++++++++++++
+ 3 files changed, 205 insertions(+)
+
+--- a/src/crypto/crypto.h
++++ b/src/crypto/crypto.h
+@@ -519,6 +519,13 @@ struct crypto_bignum * crypto_bignum_ini
+ struct crypto_bignum * crypto_bignum_init_set(const u8 *buf, size_t len);
+
+ /**
++ * crypto_bignum_init_set - Allocate memory for bignum and set the value (uint)
++ * @val: Value to set
++ * Returns: Pointer to allocated bignum or %NULL on failure
++ */
++struct crypto_bignum * crypto_bignum_init_uint(unsigned int val);
++
++/**
+ * crypto_bignum_deinit - Free bignum
+ * @n: Bignum from crypto_bignum_init() or crypto_bignum_init_set()
+ * @clear: Whether to clear the value from memory
+@@ -613,6 +620,19 @@ int crypto_bignum_div(const struct crypt
+ struct crypto_bignum *c);
+
+ /**
++ * crypto_bignum_addmod - d = a + b (mod c)
++ * @a: Bignum
++ * @b: Bignum
++ * @c: Bignum
++ * @d: Bignum; used to store the result of (a + b) % c
++ * Returns: 0 on success, -1 on failure
++ */
++int crypto_bignum_addmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ const struct crypto_bignum *c,
++ struct crypto_bignum *d);
++
++/**
+ * crypto_bignum_mulmod - d = a * b (mod c)
+ * @a: Bignum
+ * @b: Bignum
+@@ -626,6 +646,28 @@ int crypto_bignum_mulmod(const struct cr
+ struct crypto_bignum *d);
+
+ /**
++ * crypto_bignum_sqrmod - c = a^2 (mod b)
++ * @a: Bignum
++ * @b: Bignum
++ * @c: Bignum; used to store the result of a^2 % b
++ * Returns: 0 on success, -1 on failure
++ */
++int crypto_bignum_sqrmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ struct crypto_bignum *c);
++
++/**
++ * crypto_bignum_sqrtmod - returns sqrt(a) (mod b)
++ * @a: Bignum
++ * @b: Bignum
++ * @c: Bignum; used to store the result
++ * Returns: 0 on success, -1 on failure
++ */
++int crypto_bignum_sqrtmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ struct crypto_bignum *c);
++
++/**
+ * crypto_bignum_rshift - r = a >> n
+ * @a: Bignum
+ * @n: Number of bits
+@@ -731,6 +773,9 @@ const struct crypto_bignum * crypto_ec_g
+ */
+ const struct crypto_bignum * crypto_ec_get_order(struct crypto_ec *e);
+
++const struct crypto_bignum * crypto_ec_get_a(struct crypto_ec *e);
++const struct crypto_bignum * crypto_ec_get_b(struct crypto_ec *e);
++
+ /**
+ * struct crypto_ec_point - Elliptic curve point
+ *
+--- a/src/crypto/crypto_openssl.c
++++ b/src/crypto/crypto_openssl.c
+@@ -1283,6 +1283,24 @@ struct crypto_bignum * crypto_bignum_ini
+ }
+
+
++struct crypto_bignum * crypto_bignum_init_uint(unsigned int val)
++{
++ BIGNUM *bn;
++
++ if (TEST_FAIL())
++ return NULL;
++
++ bn = BN_new();
++ if (!bn)
++ return NULL;
++ if (BN_set_word(bn, val) != 1) {
++ BN_free(bn);
++ return NULL;
++ }
++ return (struct crypto_bignum *) bn;
++}
++
++
+ void crypto_bignum_deinit(struct crypto_bignum *n, int clear)
+ {
+ if (clear)
+@@ -1449,6 +1467,28 @@ int crypto_bignum_div(const struct crypt
+ }
+
+
++int crypto_bignum_addmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ const struct crypto_bignum *c,
++ struct crypto_bignum *d)
++{
++ int res;
++ BN_CTX *bnctx;
++
++ if (TEST_FAIL())
++ return -1;
++
++ bnctx = BN_CTX_new();
++ if (!bnctx)
++ return -1;
++ res = BN_mod_add((BIGNUM *) d, (const BIGNUM *) a, (const BIGNUM *) b,
++ (const BIGNUM *) c, bnctx);
++ BN_CTX_free(bnctx);
++
++ return res ? 0 : -1;
++}
++
++
+ int crypto_bignum_mulmod(const struct crypto_bignum *a,
+ const struct crypto_bignum *b,
+ const struct crypto_bignum *c,
+@@ -1472,6 +1512,48 @@ int crypto_bignum_mulmod(const struct cr
+ }
+
+
++int crypto_bignum_sqrmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ struct crypto_bignum *c)
++{
++ int res;
++ BN_CTX *bnctx;
++
++ if (TEST_FAIL())
++ return -1;
++
++ bnctx = BN_CTX_new();
++ if (!bnctx)
++ return -1;
++ res = BN_mod_sqr((BIGNUM *) c, (const BIGNUM *) a, (const BIGNUM *) b,
++ bnctx);
++ BN_CTX_free(bnctx);
++
++ return res ? 0 : -1;
++}
++
++
++int crypto_bignum_sqrtmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ struct crypto_bignum *c)
++{
++ BN_CTX *bnctx;
++ BIGNUM *res;
++
++ if (TEST_FAIL())
++ return -1;
++
++ bnctx = BN_CTX_new();
++ if (!bnctx)
++ return -1;
++ res = BN_mod_sqrt((BIGNUM *) c, (const BIGNUM *) a, (const BIGNUM *) b,
++ bnctx);
++ BN_CTX_free(bnctx);
++
++ return res ? 0 : -1;
++}
++
++
+ int crypto_bignum_rshift(const struct crypto_bignum *a, int n,
+ struct crypto_bignum *r)
+ {
+@@ -1682,6 +1764,18 @@ const struct crypto_bignum * crypto_ec_g
+ }
+
+
++const struct crypto_bignum * crypto_ec_get_a(struct crypto_ec *e)
++{
++ return (const struct crypto_bignum *) e->a;
++}
++
++
++const struct crypto_bignum * crypto_ec_get_b(struct crypto_ec *e)
++{
++ return (const struct crypto_bignum *) e->b;
++}
++
++
+ void crypto_ec_point_deinit(struct crypto_ec_point *p, int clear)
+ {
+ if (clear)
+--- a/src/crypto/crypto_wolfssl.c
++++ b/src/crypto/crypto_wolfssl.c
+@@ -1042,6 +1042,26 @@ struct crypto_bignum * crypto_bignum_ini
+ }
+
+
++struct crypto_bignum * crypto_bignum_init_uint(unsigned int val)
++{
++ mp_int *a;
++
++ if (TEST_FAIL())
++ return NULL;
++
++ a = (mp_int *) crypto_bignum_init();
++ if (!a)
++ return NULL;
++
++ if (mp_set_int(a, val) != MP_OKAY) {
++ os_free(a);
++ a = NULL;
++ }
++
++ return (struct crypto_bignum *) a;
++}
++
++
+ void crypto_bignum_deinit(struct crypto_bignum *n, int clear)
+ {
+ if (!n)
+@@ -1168,6 +1188,19 @@ int crypto_bignum_div(const struct crypt
+ }
+
+
++int crypto_bignum_addmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ const struct crypto_bignum *c,
++ struct crypto_bignum *d)
++{
++ if (TEST_FAIL())
++ return -1;
++
++ return mp_addmod((mp_int *) a, (mp_int *) b, (mp_int *) c,
++ (mp_int *) d) == MP_OKAY ? 0 : -1;
++}
++
++
+ int crypto_bignum_mulmod(const struct crypto_bignum *a,
+ const struct crypto_bignum *b,
+ const struct crypto_bignum *m,
+@@ -1181,6 +1214,27 @@ int crypto_bignum_mulmod(const struct cr
+ }
+
+
++int crypto_bignum_sqrmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ struct crypto_bignum *c)
++{
++ if (TEST_FAIL())
++ return -1;
++
++ return mp_sqrmod((mp_int *) a, (mp_int *) b,
++ (mp_int *) c) == MP_OKAY ? 0 : -1;
++}
++
++
++int crypto_bignum_sqrtmod(const struct crypto_bignum *a,
++ const struct crypto_bignum *b,
++ struct crypto_bignum *c)
++{
++ /* TODO */
++ return -1;
++}
++
++
+ int crypto_bignum_rshift(const struct crypto_bignum *a, int n,
+ struct crypto_bignum *r)
+ {
+@@ -1386,6 +1440,18 @@ const struct crypto_bignum * crypto_ec_g
+ }
+
+
++const struct crypto_bignum * crypto_ec_get_a(struct crypto_ec *e)
++{
++ return (const struct crypto_bignum *) &e->a;
++}
++
++
++const struct crypto_bignum * crypto_ec_get_b(struct crypto_ec *e)
++{
++ return (const struct crypto_bignum *) &e->b;
++}
++
++
+ void crypto_ec_point_deinit(struct crypto_ec_point *p, int clear)
+ {
+ ecc_point *point = (ecc_point *) p;
diff --git a/package/network/services/hostapd/patches/082-dragonfly-Add-sqrt-helper-function.patch b/package/network/services/hostapd/patches/082-dragonfly-Add-sqrt-helper-function.patch
new file mode 100644
index 0000000000..b8b1e078b0
--- /dev/null
+++ b/package/network/services/hostapd/patches/082-dragonfly-Add-sqrt-helper-function.patch
@@ -0,0 +1,65 @@
+From 2232d3d5f188b65dbb6c823ac62175412739eb16 Mon Sep 17 00:00:00 2001
+From: Jouni Malinen <j at w1.fi>
+Date: Fri, 7 Jan 2022 13:47:16 +0200
+Subject: [PATCH 2/4] dragonfly: Add sqrt() helper function
+
+This is a backport of "SAE: Move sqrt() implementation into a helper
+function" to introduce the helper function needed for the following
+patches.
+
+Signed-off-by: Jouni Malinen <j at w1.fi>
+---
+ src/common/dragonfly.c | 34 ++++++++++++++++++++++++++++++++++
+ src/common/dragonfly.h | 2 ++
+ 2 files changed, 36 insertions(+)
+
+--- a/src/common/dragonfly.c
++++ b/src/common/dragonfly.c
+@@ -213,3 +213,37 @@ int dragonfly_generate_scalar(const stru
+ "dragonfly: Unable to get randomness for own scalar");
+ return -1;
+ }
++
++
++/* res = sqrt(val) */
++int dragonfly_sqrt(struct crypto_ec *ec, const struct crypto_bignum *val,
++ struct crypto_bignum *res)
++{
++ const struct crypto_bignum *prime;
++ struct crypto_bignum *tmp, *one;
++ int ret = 0;
++ u8 prime_bin[DRAGONFLY_MAX_ECC_PRIME_LEN];
++ size_t prime_len;
++
++ /* For prime p such that p = 3 mod 4, sqrt(w) = w^((p+1)/4) mod p */
++
++ prime = crypto_ec_get_prime(ec);
++ prime_len = crypto_ec_prime_len(ec);
++ tmp = crypto_bignum_init();
++ one = crypto_bignum_init_uint(1);
++
++ if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin),
++ prime_len) < 0 ||
++ (prime_bin[prime_len - 1] & 0x03) != 3 ||
++ !tmp || !one ||
++ /* tmp = (p+1)/4 */
++ crypto_bignum_add(prime, one, tmp) < 0 ||
++ crypto_bignum_rshift(tmp, 2, tmp) < 0 ||
++ /* res = sqrt(val) */
++ crypto_bignum_exptmod(val, tmp, prime, res) < 0)
++ ret = -1;
++
++ crypto_bignum_deinit(tmp, 0);
++ crypto_bignum_deinit(one, 0);
++ return ret;
++}
+--- a/src/common/dragonfly.h
++++ b/src/common/dragonfly.h
+@@ -27,5 +27,7 @@ int dragonfly_generate_scalar(const stru
+ struct crypto_bignum *_rand,
+ struct crypto_bignum *_mask,
+ struct crypto_bignum *scalar);
++int dragonfly_sqrt(struct crypto_ec *ec, const struct crypto_bignum *val,
++ struct crypto_bignum *res);
+
+ #endif /* DRAGONFLY_H */
diff --git a/package/network/services/hostapd/patches/083-SAE-Derive-the-y-coordinate-for-PWE-with-own-impleme.patch b/package/network/services/hostapd/patches/083-SAE-Derive-the-y-coordinate-for-PWE-with-own-impleme.patch
new file mode 100644
index 0000000000..d2a46c68f5
--- /dev/null
+++ b/package/network/services/hostapd/patches/083-SAE-Derive-the-y-coordinate-for-PWE-with-own-impleme.patch
@@ -0,0 +1,94 @@
+From fe534b0baaa8c0e6ddeb24cf529d6e50e33dc501 Mon Sep 17 00:00:00 2001
+From: Jouni Malinen <j at w1.fi>
+Date: Fri, 7 Jan 2022 13:47:16 +0200
+Subject: [PATCH 3/4] SAE: Derive the y coordinate for PWE with own
+ implementation
+
+The crypto_ec_point_solve_y_coord() wrapper function might not use
+constant time operations in the crypto library and as such, could leak
+side channel information about the password that is used to generate the
+PWE in the hunting and pecking loop. As such, calculate the two possible
+y coordinate values and pick the correct one to use with constant time
+selection.
+
+Signed-off-by: Jouni Malinen <j at w1.fi>
+---
+ src/common/sae.c | 47 +++++++++++++++++++++++++++++++++--------------
+ 1 file changed, 33 insertions(+), 14 deletions(-)
+
+--- a/src/common/sae.c
++++ b/src/common/sae.c
+@@ -286,14 +286,16 @@ static int sae_derive_pwe_ecc(struct sae
+ int pwd_seed_odd = 0;
+ u8 prime[SAE_MAX_ECC_PRIME_LEN];
+ size_t prime_len;
+- struct crypto_bignum *x = NULL, *qr = NULL, *qnr = NULL;
++ struct crypto_bignum *x = NULL, *y = NULL, *qr = NULL, *qnr = NULL;
+ u8 x_bin[SAE_MAX_ECC_PRIME_LEN];
+ u8 x_cand_bin[SAE_MAX_ECC_PRIME_LEN];
+ u8 qr_bin[SAE_MAX_ECC_PRIME_LEN];
+ u8 qnr_bin[SAE_MAX_ECC_PRIME_LEN];
++ u8 x_y[2 * SAE_MAX_ECC_PRIME_LEN];
+ int res = -1;
+ u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_*
+ * mask */
++ unsigned int is_eq;
+
+ os_memset(x_bin, 0, sizeof(x_bin));
+
+@@ -402,25 +404,42 @@ static int sae_derive_pwe_ecc(struct sae
+ goto fail;
+ }
+
+- if (!sae->tmp->pwe_ecc)
+- sae->tmp->pwe_ecc = crypto_ec_point_init(sae->tmp->ec);
+- if (!sae->tmp->pwe_ecc)
+- res = -1;
+- else
+- res = crypto_ec_point_solve_y_coord(sae->tmp->ec,
+- sae->tmp->pwe_ecc, x,
+- pwd_seed_odd);
+- if (res < 0) {
+- /*
+- * This should not happen since we already checked that there
+- * is a result.
+- */
++ /* y = sqrt(x^3 + ax + b) mod p
++ * if LSB(save) == LSB(y): PWE = (x, y)
++ * else: PWE = (x, p - y)
++ *
++ * Calculate y and the two possible values for PWE and after that,
++ * use constant time selection to copy the correct alternative.
++ */
++ y = crypto_ec_point_compute_y_sqr(sae->tmp->ec, x);
++ if (!y ||
++ dragonfly_sqrt(sae->tmp->ec, y, y) < 0 ||
++ crypto_bignum_to_bin(y, x_y, SAE_MAX_ECC_PRIME_LEN,
++ prime_len) < 0 ||
++ crypto_bignum_sub(sae->tmp->prime, y, y) < 0 ||
++ crypto_bignum_to_bin(y, x_y + SAE_MAX_ECC_PRIME_LEN,
++ SAE_MAX_ECC_PRIME_LEN, prime_len) < 0) {
+ wpa_printf(MSG_DEBUG, "SAE: Could not solve y");
++ goto fail;
++ }
++
++ is_eq = const_time_eq(pwd_seed_odd, x_y[prime_len - 1] & 0x01);
++ const_time_select_bin(is_eq, x_y, x_y + SAE_MAX_ECC_PRIME_LEN,
++ prime_len, x_y + prime_len);
++ os_memcpy(x_y, x_bin, prime_len);
++ wpa_hexdump_key(MSG_DEBUG, "SAE: PWE", x_y, 2 * prime_len);
++ crypto_ec_point_deinit(sae->tmp->pwe_ecc, 1);
++ sae->tmp->pwe_ecc = crypto_ec_point_from_bin(sae->tmp->ec, x_y);
++ if (!sae->tmp->pwe_ecc) {
++ wpa_printf(MSG_DEBUG, "SAE: Could not generate PWE");
++ res = -1;
+ }
+
+ fail:
++ forced_memzero(x_y, sizeof(x_y));
+ crypto_bignum_deinit(qr, 0);
+ crypto_bignum_deinit(qnr, 0);
++ crypto_bignum_deinit(y, 1);
+ os_free(dummy_password);
+ bin_clear_free(tmp_password, password_len);
+ crypto_bignum_deinit(x, 1);
diff --git a/package/network/services/hostapd/patches/084-EAP-pwd-Derive-the-y-coordinate-for-PWE-with-own-imp.patch b/package/network/services/hostapd/patches/084-EAP-pwd-Derive-the-y-coordinate-for-PWE-with-own-imp.patch
new file mode 100644
index 0000000000..c5ddddcec3
--- /dev/null
+++ b/package/network/services/hostapd/patches/084-EAP-pwd-Derive-the-y-coordinate-for-PWE-with-own-imp.patch
@@ -0,0 +1,108 @@
+From 603cd880e7f90595482658a7136fa6a7be5cb485 Mon Sep 17 00:00:00 2001
+From: Jouni Malinen <j at w1.fi>
+Date: Fri, 7 Jan 2022 18:52:27 +0200
+Subject: [PATCH 4/4] EAP-pwd: Derive the y coordinate for PWE with own
+ implementation
+
+The crypto_ec_point_solve_y_coord() wrapper function might not use
+constant time operations in the crypto library and as such, could leak
+side channel information about the password that is used to generate the
+PWE in the hunting and pecking loop. As such, calculate the two possible
+y coordinate values and pick the correct one to use with constant time
+selection.
+
+Signed-off-by: Jouni Malinen <j at w1.fi>
+---
+ src/eap_common/eap_pwd_common.c | 46 ++++++++++++++++++++++++++-------
+ 1 file changed, 36 insertions(+), 10 deletions(-)
+
+--- a/src/eap_common/eap_pwd_common.c
++++ b/src/eap_common/eap_pwd_common.c
+@@ -127,7 +127,8 @@ int compute_password_element(EAP_PWD_gro
+ u8 qr_or_qnr_bin[MAX_ECC_PRIME_LEN];
+ u8 x_bin[MAX_ECC_PRIME_LEN];
+ u8 prime_bin[MAX_ECC_PRIME_LEN];
+- struct crypto_bignum *tmp2 = NULL;
++ u8 x_y[2 * MAX_ECC_PRIME_LEN];
++ struct crypto_bignum *tmp2 = NULL, *y = NULL;
+ struct crypto_hash *hash;
+ unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr;
+ int ret = 0, res;
+@@ -139,6 +140,7 @@ int compute_password_element(EAP_PWD_gro
+ u8 found_ctr = 0, is_odd = 0;
+ int cmp_prime;
+ unsigned int in_range;
++ unsigned int is_eq;
+
+ if (grp->pwe)
+ return -1;
+@@ -151,11 +153,6 @@ int compute_password_element(EAP_PWD_gro
+ if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin),
+ primebytelen) < 0)
+ return -1;
+- grp->pwe = crypto_ec_point_init(grp->group);
+- if (!grp->pwe) {
+- wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums");
+- goto fail;
+- }
+
+ if ((prfbuf = os_malloc(primebytelen)) == NULL) {
+ wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf "
+@@ -261,10 +258,37 @@ int compute_password_element(EAP_PWD_gro
+ */
+ crypto_bignum_deinit(x_candidate, 1);
+ x_candidate = crypto_bignum_init_set(x_bin, primebytelen);
+- if (!x_candidate ||
+- crypto_ec_point_solve_y_coord(grp->group, grp->pwe, x_candidate,
+- is_odd) != 0) {
+- wpa_printf(MSG_INFO, "EAP-pwd: Could not solve for y");
++ if (!x_candidate)
++ goto fail;
++
++ /* y = sqrt(x^3 + ax + b) mod p
++ * if LSB(y) == LSB(pwd-seed): PWE = (x, y)
++ * else: PWE = (x, p - y)
++ *
++ * Calculate y and the two possible values for PWE and after that,
++ * use constant time selection to copy the correct alternative.
++ */
++ y = crypto_ec_point_compute_y_sqr(grp->group, x_candidate);
++ if (!y ||
++ dragonfly_sqrt(grp->group, y, y) < 0 ||
++ crypto_bignum_to_bin(y, x_y, MAX_ECC_PRIME_LEN, primebytelen) < 0 ||
++ crypto_bignum_sub(prime, y, y) < 0 ||
++ crypto_bignum_to_bin(y, x_y + MAX_ECC_PRIME_LEN,
++ MAX_ECC_PRIME_LEN, primebytelen) < 0) {
++ wpa_printf(MSG_DEBUG, "SAE: Could not solve y");
++ goto fail;
++ }
++
++ /* Constant time selection of the y coordinate from the two
++ * options */
++ is_eq = const_time_eq(is_odd, x_y[primebytelen - 1] & 0x01);
++ const_time_select_bin(is_eq, x_y, x_y + MAX_ECC_PRIME_LEN,
++ primebytelen, x_y + primebytelen);
++ os_memcpy(x_y, x_bin, primebytelen);
++ wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: PWE", x_y, 2 * primebytelen);
++ grp->pwe = crypto_ec_point_from_bin(grp->group, x_y);
++ if (!grp->pwe) {
++ wpa_printf(MSG_DEBUG, "EAP-pwd: Could not generate PWE");
+ goto fail;
+ }
+
+@@ -289,6 +313,7 @@ int compute_password_element(EAP_PWD_gro
+ /* cleanliness and order.... */
+ crypto_bignum_deinit(x_candidate, 1);
+ crypto_bignum_deinit(tmp2, 1);
++ crypto_bignum_deinit(y, 1);
+ crypto_bignum_deinit(qr, 1);
+ crypto_bignum_deinit(qnr, 1);
+ bin_clear_free(prfbuf, primebytelen);
+@@ -296,6 +321,7 @@ int compute_password_element(EAP_PWD_gro
+ os_memset(qnr_bin, 0, sizeof(qnr_bin));
+ os_memset(qr_or_qnr_bin, 0, sizeof(qr_or_qnr_bin));
+ os_memset(pwe_digest, 0, sizeof(pwe_digest));
++ forced_memzero(x_y, sizeof(x_y));
+
+ return ret;
+ }
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