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SAE: Add side-channel protection to PWE derivation with ECC
This replaces the earlier IEEE Std 802.11-2012 algorithm with the design from P802.11-REVmc/D4.0. Things brings in a blinding technique for determining whether the pwd-seed results in a suitable PWE value. Signed-off-by: Jouni Malinen <j@w1.fi>
This commit is contained in:
Jouni Malinen
parent
16841ab246
commit
eb5fee0bf5
250
src/common/sae.c
250
src/common/sae.c
@ -1,6 +1,6 @@
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/*
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* Simultaneous authentication of equals
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* Copyright (c) 2012-2013, Jouni Malinen <j@w1.fi>
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* Copyright (c) 2012-2015, Jouni Malinen <j@w1.fi>
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*
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* This software may be distributed under the terms of the BSD license.
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* See README for more details.
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@ -169,17 +169,107 @@ static void sae_pwd_seed_key(const u8 *addr1, const u8 *addr2, u8 *key)
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}
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static int sae_test_pwd_seed_ecc(struct sae_data *sae, const u8 *pwd_seed,
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struct crypto_ec_point *pwe)
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static struct crypto_bignum *
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get_rand_1_to_p_1(const u8 *prime, size_t prime_len, size_t prime_bits,
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int *r_odd)
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{
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u8 pwd_value[SAE_MAX_ECC_PRIME_LEN], prime[SAE_MAX_ECC_PRIME_LEN];
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struct crypto_bignum *x;
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int y_bit;
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for (;;) {
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struct crypto_bignum *r;
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u8 tmp[SAE_MAX_ECC_PRIME_LEN];
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if (random_get_bytes(tmp, prime_len) < 0)
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break;
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if (prime_bits % 8)
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buf_shift_right(tmp, prime_len, 8 - prime_bits % 8);
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if (os_memcmp(tmp, prime, prime_len) >= 0)
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continue;
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r = crypto_bignum_init_set(tmp, prime_len);
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if (!r)
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break;
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if (crypto_bignum_is_zero(r)) {
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crypto_bignum_deinit(r, 0);
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continue;
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}
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*r_odd = tmp[prime_len - 1] & 0x01;
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return r;
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}
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return NULL;
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}
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static int is_quadratic_residue_blind(struct sae_data *sae,
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const u8 *prime, size_t bits,
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const struct crypto_bignum *qr,
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const struct crypto_bignum *qnr,
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const struct crypto_bignum *y_sqr)
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{
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struct crypto_bignum *r, *num;
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int r_odd, check, res = -1;
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/*
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* Use the blinding technique to mask y_sqr while determining
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* whether it is a quadratic residue modulo p to avoid leaking
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* timing information while determining the Legendre symbol.
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*
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* v = y_sqr
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* r = a random number between 1 and p-1, inclusive
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* num = (v * r * r) modulo p
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*/
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r = get_rand_1_to_p_1(prime, sae->tmp->prime_len, bits, &r_odd);
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if (!r)
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return -1;
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num = crypto_bignum_init();
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if (!num ||
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crypto_bignum_mulmod(y_sqr, r, sae->tmp->prime, num) < 0 ||
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crypto_bignum_mulmod(num, r, sae->tmp->prime, num) < 0)
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goto fail;
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if (r_odd) {
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/*
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* num = (num * qr) module p
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* LGR(num, p) = 1 ==> quadratic residue
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*/
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if (crypto_bignum_mulmod(num, qr, sae->tmp->prime, num) < 0)
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goto fail;
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check = 1;
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} else {
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/*
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* num = (num * qnr) module p
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* LGR(num, p) = -1 ==> quadratic residue
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*/
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if (crypto_bignum_mulmod(num, qnr, sae->tmp->prime, num) < 0)
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goto fail;
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check = -1;
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}
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res = crypto_bignum_legendre(num, sae->tmp->prime);
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if (res == -2) {
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res = -1;
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goto fail;
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}
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res = res == check;
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fail:
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crypto_bignum_deinit(num, 1);
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crypto_bignum_deinit(r, 1);
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return res;
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}
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static int sae_test_pwd_seed_ecc(struct sae_data *sae, const u8 *pwd_seed,
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const u8 *prime,
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const struct crypto_bignum *qr,
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const struct crypto_bignum *qnr,
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struct crypto_bignum **ret_x_cand)
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{
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u8 pwd_value[SAE_MAX_ECC_PRIME_LEN];
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struct crypto_bignum *y_sqr, *x_cand;
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int res;
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size_t bits;
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if (crypto_bignum_to_bin(sae->tmp->prime, prime, sizeof(prime),
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sae->tmp->prime_len) < 0)
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return -1;
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*ret_x_cand = NULL;
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wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-seed", pwd_seed, SHA256_MAC_LEN);
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@ -195,20 +285,23 @@ static int sae_test_pwd_seed_ecc(struct sae_data *sae, const u8 *pwd_seed,
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if (os_memcmp(pwd_value, prime, sae->tmp->prime_len) >= 0)
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return 0;
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y_bit = pwd_seed[SHA256_MAC_LEN - 1] & 0x01;
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x = crypto_bignum_init_set(pwd_value, sae->tmp->prime_len);
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if (x == NULL)
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x_cand = crypto_bignum_init_set(pwd_value, sae->tmp->prime_len);
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if (!x_cand)
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return -1;
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y_sqr = crypto_ec_point_compute_y_sqr(sae->tmp->ec, x_cand);
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if (!y_sqr) {
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crypto_bignum_deinit(x_cand, 1);
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return -1;
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if (crypto_ec_point_solve_y_coord(sae->tmp->ec, pwe, x, y_bit) < 0) {
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crypto_bignum_deinit(x, 0);
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wpa_printf(MSG_DEBUG, "SAE: No solution found");
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return 0;
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}
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crypto_bignum_deinit(x, 0);
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wpa_printf(MSG_DEBUG, "SAE: PWE found");
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res = is_quadratic_residue_blind(sae, prime, bits, qr, qnr, y_sqr);
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crypto_bignum_deinit(y_sqr, 1);
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if (res <= 0) {
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crypto_bignum_deinit(x_cand, 1);
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return res;
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}
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*ret_x_cand = x_cand;
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return 1;
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}
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@ -286,6 +379,42 @@ static int sae_test_pwd_seed_ffc(struct sae_data *sae, const u8 *pwd_seed,
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}
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static int get_random_qr_qnr(const u8 *prime, size_t prime_len,
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const struct crypto_bignum *prime_bn,
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size_t prime_bits, struct crypto_bignum **qr,
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struct crypto_bignum **qnr)
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{
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*qr = NULL;
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*qnr = NULL;
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while (!(*qr) || !(*qnr)) {
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u8 tmp[SAE_MAX_ECC_PRIME_LEN];
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struct crypto_bignum *q;
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int res;
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if (random_get_bytes(tmp, prime_len) < 0)
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break;
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if (prime_bits % 8)
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buf_shift_right(tmp, prime_len, 8 - prime_bits % 8);
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if (os_memcmp(tmp, prime, prime_len) >= 0)
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continue;
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q = crypto_bignum_init_set(tmp, prime_len);
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if (!q)
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break;
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res = crypto_bignum_legendre(q, prime_bn);
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if (res == 1 && !(*qr))
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*qr = q;
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else if (res == -1 && !(*qnr))
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*qnr = q;
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else
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crypto_bignum_deinit(q, 0);
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}
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return (*qr && *qnr) ? 0 : -1;
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}
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static int sae_derive_pwe_ecc(struct sae_data *sae, const u8 *addr1,
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const u8 *addr2, const u8 *password,
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size_t password_len)
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@ -294,16 +423,25 @@ static int sae_derive_pwe_ecc(struct sae_data *sae, const u8 *addr1,
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u8 addrs[2 * ETH_ALEN];
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const u8 *addr[2];
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size_t len[2];
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int found = 0;
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struct crypto_ec_point *pwe_tmp;
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int pwd_seed_odd = 0;
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u8 prime[SAE_MAX_ECC_PRIME_LEN];
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size_t prime_len;
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struct crypto_bignum *x = NULL, *qr, *qnr;
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size_t bits;
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int res;
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if (sae->tmp->pwe_ecc == NULL) {
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sae->tmp->pwe_ecc = crypto_ec_point_init(sae->tmp->ec);
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if (sae->tmp->pwe_ecc == NULL)
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return -1;
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}
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pwe_tmp = crypto_ec_point_init(sae->tmp->ec);
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if (pwe_tmp == NULL)
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prime_len = sae->tmp->prime_len;
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if (crypto_bignum_to_bin(sae->tmp->prime, prime, sizeof(prime),
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prime_len) < 0)
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return -1;
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bits = crypto_ec_prime_len_bits(sae->tmp->ec);
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/*
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* Create a random quadratic residue (qr) and quadratic non-residue
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* (qnr) modulo p for blinding purposes during the loop.
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*/
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if (get_random_qr_qnr(prime, prime_len, sae->tmp->prime, bits,
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&qr, &qnr) < 0)
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return -1;
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wpa_hexdump_ascii_key(MSG_DEBUG, "SAE: password",
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@ -326,9 +464,9 @@ static int sae_derive_pwe_ecc(struct sae_data *sae, const u8 *addr1,
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* attacks that attempt to determine the number of iterations required
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* in the loop.
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*/
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for (counter = 1; counter <= k || !found; counter++) {
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for (counter = 1; counter <= k || !x; counter++) {
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u8 pwd_seed[SHA256_MAC_LEN];
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int res;
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struct crypto_bignum *x_cand;
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if (counter > 200) {
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/* This should not happen in practice */
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@ -340,25 +478,51 @@ static int sae_derive_pwe_ecc(struct sae_data *sae, const u8 *addr1,
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if (hmac_sha256_vector(addrs, sizeof(addrs), 2, addr, len,
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pwd_seed) < 0)
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break;
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res = sae_test_pwd_seed_ecc(sae, pwd_seed,
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found ? pwe_tmp :
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sae->tmp->pwe_ecc);
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prime, qr, qnr, &x_cand);
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if (res < 0)
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break;
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if (res == 0)
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continue;
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if (found) {
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wpa_printf(MSG_DEBUG, "SAE: Ignore this PWE (one was "
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"already selected)");
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} else {
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wpa_printf(MSG_DEBUG, "SAE: Use this PWE");
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found = 1;
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goto fail;
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if (res > 0 && !x) {
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wpa_printf(MSG_DEBUG,
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"SAE: Selected pwd-seed with counter %u",
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counter);
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x = x_cand;
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pwd_seed_odd = pwd_seed[SHA256_MAC_LEN - 1] & 0x01;
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os_memset(pwd_seed, 0, sizeof(pwd_seed));
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} else if (res > 0) {
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crypto_bignum_deinit(x_cand, 1);
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}
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}
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crypto_ec_point_deinit(pwe_tmp, 1);
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if (!x) {
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wpa_printf(MSG_DEBUG, "SAE: Could not generate PWE");
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res = -1;
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goto fail;
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}
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return found ? 0 : -1;
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if (!sae->tmp->pwe_ecc)
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sae->tmp->pwe_ecc = crypto_ec_point_init(sae->tmp->ec);
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if (!sae->tmp->pwe_ecc)
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res = -1;
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else
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res = crypto_ec_point_solve_y_coord(sae->tmp->ec,
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sae->tmp->pwe_ecc, x,
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pwd_seed_odd);
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crypto_bignum_deinit(x, 1);
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if (res < 0) {
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/*
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* This should not happen since we already checked that there
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* is a result.
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*/
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wpa_printf(MSG_DEBUG, "SAE: Could not solve y");
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}
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fail:
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crypto_bignum_deinit(qr, 0);
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crypto_bignum_deinit(qnr, 0);
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return res;
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}
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