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iwd/src/sae.c

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/*
*
* Wireless daemon for Linux
*
* Copyright (C) 2018-2019 Intel Corporation. All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <ell/ell.h>
#include "src/missing.h"
#include "src/util.h"
#include "src/ie.h"
#include "src/handshake.h"
#include "src/crypto.h"
#include "src/mpdu.h"
#include "src/auth-proto.h"
#include "src/sae.h"
/* SHA-512 is the highest supported hashing function as of 802.11-2020 */
#define SAE_MAX_HASH_LEN 64
#define SAE_RETRANSMIT_TIMEOUT 2
#define SAE_SYNC_MAX 3
#define SAE_MAX_ASSOC_RETRY 3
enum sae_state {
SAE_STATE_NOTHING = 0,
SAE_STATE_COMMITTED = 1,
SAE_STATE_CONFIRMED = 2,
SAE_STATE_ACCEPTED = 3,
};
struct sae_sm {
struct auth_proto ap;
struct handshake_state *handshake;
struct l_ecc_point *pwe;
enum sae_state state;
const struct l_ecc_curve *curve;
unsigned int group;
int group_retry;
uint16_t *rejected_groups;
struct l_ecc_scalar *rand;
struct l_ecc_scalar *scalar;
struct l_ecc_scalar *p_scalar;
struct l_ecc_point *element;
struct l_ecc_point *p_element;
uint16_t send_confirm;
uint8_t kck[SAE_MAX_HASH_LEN];
uint8_t pmk[32];
uint8_t pmkid[16];
uint8_t *token;
size_t token_len;
/* number of state resyncs that have occurred */
uint16_t sync;
/* number of SAE confirm messages that have been sent */
uint16_t sc;
/* received value of the send-confirm counter */
uint16_t rc;
/* remote peer */
uint8_t peer[6];
uint8_t assoc_retry;
sae_tx_authenticate_func_t tx_auth;
sae_tx_associate_func_t tx_assoc;
void *user_data;
enum crypto_sae sae_type;
};
static enum mmpdu_status_code sae_status_code(struct sae_sm *sm)
{
switch (sm->sae_type) {
case CRYPTO_SAE_LOOPING:
return MMPDU_STATUS_CODE_SUCCESS;
case CRYPTO_SAE_HASH_TO_ELEMENT:
return MMPDU_STATUS_CODE_SAE_HASH_TO_ELEMENT;
}
return MMPDU_STATUS_CODE_UNSPECIFIED;
}
static void sae_rejected_groups_append(struct sae_sm *sm, uint16_t group)
{
uint16_t i;
if (!sm->rejected_groups) {
sm->rejected_groups = reallocarray(NULL, 2, sizeof(uint16_t));
sm->rejected_groups[0] = 1;
sm->rejected_groups[1] = group;
return;
}
for (i = 1; i <= sm->rejected_groups[0]; i++)
if (sm->rejected_groups[i] == group)
return;
sm->rejected_groups = reallocarray(sm->rejected_groups,
i + 1, sizeof(uint16_t));
sm->rejected_groups[0] += 1;
sm->rejected_groups[i] = group;
}
static void sae_reset_state(struct sae_sm *sm)
{
l_ecc_scalar_free(sm->scalar);
sm->scalar = NULL;
l_ecc_scalar_free(sm->p_scalar);
sm->p_scalar = NULL;
l_ecc_scalar_free(sm->rand);
sm->rand = NULL;
l_ecc_point_free(sm->element);
sm->element = NULL;
l_ecc_point_free(sm->p_element);
sm->p_element = NULL;
l_ecc_point_free(sm->pwe);
sm->pwe = NULL;
}
static int sae_choose_next_group(struct sae_sm *sm)
{
const unsigned int *ecc_groups = l_ecc_supported_ike_groups();
bool reset = sm->group_retry >= 0;
do {
sm->group_retry++;
if (ecc_groups[sm->group_retry] == 0)
return -ENOENT;
} while (sm->sae_type != CRYPTO_SAE_LOOPING &&
!sm->handshake->ecc_sae_pts[sm->group_retry]);
if (reset)
sae_reset_state(sm);
sm->group = ecc_groups[sm->group_retry];
sm->curve = l_ecc_curve_from_ike_group(sm->group);
return 0;
}
static int sae_valid_group(struct sae_sm *sm, unsigned int group)
{
const unsigned int *ecc_groups = l_ecc_supported_ike_groups();
unsigned int i;
for (i = sm->group_retry; ecc_groups[i]; i++) {
if (ecc_groups[i] != group)
continue;
if (sm->sae_type != CRYPTO_SAE_LOOPING &&
!sm->handshake->ecc_sae_pts[i])
continue;
return i;
}
return -ENOENT;
}
static bool sae_pwd_seed(const uint8_t *addr1, const uint8_t *addr2,
uint8_t *base, size_t base_len,
uint8_t counter, uint8_t *out)
{
uint8_t key[12];
if (memcmp(addr1, addr2, 6) > 0) {
memcpy(key, addr1, 6);
memcpy(key + 6, addr2, 6);
} else {
memcpy(key, addr2, 6);
memcpy(key + 6, addr1, 6);
}
return hkdf_extract(L_CHECKSUM_SHA256, key, 12, 2, out, base, base_len,
&counter, (size_t) 1);
}
/*
* Computes KDF-256(pwd_seed, "SAE Hunting and Pecking", p). If the output is
* greater than p, the output is set to qnr, a quadratic non-residue.
* Since this happens with very low probability, using the same qnr is fine.
*/
static struct l_ecc_scalar *sae_pwd_value(const struct l_ecc_curve *curve,
uint8_t *pwd_seed, uint8_t *qnr)
{
uint8_t pwd_value[L_ECC_SCALAR_MAX_BYTES];
uint8_t prime[L_ECC_SCALAR_MAX_BYTES];
ssize_t len;
int is_in_range;
struct l_ecc_scalar *p = l_ecc_curve_get_prime(curve);
len = l_ecc_scalar_get_data(p, prime, sizeof(prime));
l_ecc_scalar_free(p);
if (!kdf_sha256(pwd_seed, 32, "SAE Hunting and Pecking",
strlen("SAE Hunting and Pecking"), prime, len,
pwd_value, len))
return NULL;
/*
* If pwd_value >= prime, this iteration should fail. We need a smooth
* control flow, so we need to continue anyway.
*/
is_in_range = l_secure_memcmp(pwd_value, prime, len);
/*
* We only consider is_in_range == -1 as valid, meaning the value of the
* MSB defines the mask.
*/
is_in_range = util_secure_fill_with_msb(is_in_range);
/*
* libell has public Legendre symbol only for l_ecc_scalar, but they
* cannot be created if the coordinate is greater than the p. Hence,
* to avoid control flow dependencies, we replace pwd_value by a dummy
* quadratic non residue if we generate a value >= prime.
*/
util_secure_select((uint8_t) is_in_range, pwd_value, qnr,
pwd_value, sizeof(pwd_value));
return l_ecc_scalar_new(curve, pwd_value, sizeof(pwd_value));
}
/* IEEE 802.11-2016 - Section 12.4.2 Assumptions on SAE */
static ssize_t sae_cn(struct sae_sm *sm, uint16_t send_confirm,
struct l_ecc_scalar *scalar1,
struct l_ecc_point *element1,
struct l_ecc_scalar *scalar2,
struct l_ecc_point *element2,
uint8_t *confirm)
{
enum l_checksum_type hash =
crypto_sae_hash_from_ecc_prime_len(sm->sae_type,
l_ecc_curve_get_scalar_bytes(sm->curve));
size_t hash_len = l_checksum_digest_length(hash);
uint8_t s1[L_ECC_SCALAR_MAX_BYTES];
uint8_t s2[L_ECC_SCALAR_MAX_BYTES];
uint8_t e1[L_ECC_POINT_MAX_BYTES];
uint8_t e2[L_ECC_POINT_MAX_BYTES];
struct l_checksum *hmac;
struct iovec iov[5];
ssize_t ret;
hmac = l_checksum_new_hmac(hash, sm->kck, hash_len);
if (!hmac)
return false;
send_confirm = L_CPU_TO_LE16(send_confirm);
iov[0].iov_base = &send_confirm;
iov[0].iov_len = 2;
iov[1].iov_base = (void *) s1;
iov[1].iov_len = l_ecc_scalar_get_data(scalar1, s1, sizeof(s1));
iov[2].iov_base = (void *) e1;
iov[2].iov_len = l_ecc_point_get_data(element1, e1, sizeof(e1));
iov[3].iov_base = (void *) s2;
iov[3].iov_len = l_ecc_scalar_get_data(scalar2, s2, sizeof(s2));
iov[4].iov_base = (void *) e2;
iov[4].iov_len = l_ecc_point_get_data(element2, e2, sizeof(e2));
l_checksum_updatev(hmac, iov, 5);
ret = l_checksum_get_digest(hmac, confirm, hash_len);
l_checksum_free(hmac);
return ret;
}
static int sae_reject(struct sae_sm *sm, uint16_t transaction, uint16_t status)
{
uint8_t reject[6];
uint8_t *ptr = reject;
if (!sm->handshake->authenticator)
return -EPROTO;
/* transaction */
l_put_u16(transaction, ptr);
ptr += 2;
l_put_u16(status, ptr);
ptr += 2;
if (status == MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP) {
l_put_u16(sm->group, ptr);
ptr += 2;
}
sm->tx_auth(reject, ptr - reject, sm->user_data);
return status;
}
static struct l_ecc_scalar *sae_new_residue(const struct l_ecc_curve *curve,
bool residue)
{
struct l_ecc_scalar *s = l_ecc_scalar_new_random(curve);
while (l_ecc_scalar_legendre(s) != ((residue) ? -1 : 1)) {
l_ecc_scalar_free(s);
s = l_ecc_scalar_new_random(curve);
}
return s;
}
static uint8_t sae_is_quadradic_residue(const struct l_ecc_curve *curve,
struct l_ecc_scalar *value,
struct l_ecc_scalar *qr,
struct l_ecc_scalar *qnr)
{
uint64_t rbuf[L_ECC_MAX_DIGITS];
struct l_ecc_scalar *y_sqr = l_ecc_scalar_new(curve, NULL, 0);
struct l_ecc_scalar *r = l_ecc_scalar_new_random(curve);
struct l_ecc_scalar *num = l_ecc_scalar_new(curve, NULL, 0);
size_t bytes;
l_ecc_scalar_sum_x(y_sqr, value);
l_ecc_scalar_multiply(num, y_sqr, r);
l_ecc_scalar_multiply(num, num, r);
l_ecc_scalar_free(y_sqr);
bytes = l_ecc_scalar_get_data(r, rbuf, sizeof(rbuf));
l_ecc_scalar_free(r);
if (bytes <= 0) {
l_ecc_scalar_free(num);
return 0;
}
if (rbuf[bytes / 8 - 1] & 1) {
l_ecc_scalar_multiply(num, num, qr);
if (l_ecc_scalar_legendre(num) == -1) {
l_ecc_scalar_free(num);
return 1;
}
} else {
l_ecc_scalar_multiply(num, num, qnr);
if (l_ecc_scalar_legendre(num) == 1) {
l_ecc_scalar_free(num);
return 1;
}
}
l_ecc_scalar_free(num);
return 0;
}
/*
* IEEE 802.11-2016 Section 12.4.4.2.2
* Generation of the password element with ECC groups
*/
static struct l_ecc_point *sae_compute_pwe(const struct l_ecc_curve *curve,
const char *password,
const uint8_t *addr1,
const uint8_t *addr2)
{
uint8_t found = 0;
uint8_t is_residue;
uint8_t is_odd = 0;
uint8_t counter;
uint8_t pwd_seed[32];
uint8_t x[L_ECC_SCALAR_MAX_BYTES];
uint8_t x_cand[L_ECC_SCALAR_MAX_BYTES];
struct l_ecc_scalar *pwd_value;
uint8_t *dummy;
uint8_t *base;
size_t base_len;
struct l_ecc_scalar *qr;
struct l_ecc_scalar *qnr;
uint8_t qnr_bin[L_ECC_SCALAR_MAX_BYTES] = {0};
struct l_ecc_point *pwe;
/* create qr/qnr prior to beginning hunting-and-pecking loop */
qr = sae_new_residue(curve, true);
qnr = sae_new_residue(curve, false);
l_ecc_scalar_get_data(qnr, qnr_bin, sizeof(qnr_bin));
/*
* Allocate memory for the base, and set a random dummy to be used in
* additional iterations, once a valid value is found
*/
base_len = strlen(password);
base = l_malloc(base_len * sizeof(*base));
dummy = l_malloc(base_len * sizeof(*dummy));
l_getrandom(dummy, base_len);
/*
* Loop with constant time and memory access
* We do 30 iterations instead of the 40 recommended to achieve a
* resonnable security/complexity trade-off.
*/
for (counter = 1; counter <= 30; counter++) {
/*
* Set base to either dummy or password, depending on found's
* value.
* A non-secure version would be:
* base = (found ? dummy : password);
*/
util_secure_select(found, dummy, (uint8_t *)password,
base, base_len);
/*
* pwd-seed = H(max(addr1, addr2) || min(addr1, addr2),
* base || counter)
* pwd-value = KDF-256(pwd-seed, "SAE Hunting and Pecking", p)
*/
sae_pwd_seed(addr1, addr2, base, base_len, counter, pwd_seed);
/*
* The case pwd_value > prime is handled inside, so that
* execution can continue whatever the result is, without
* changing the outcome.
*/
pwd_value = sae_pwd_value(curve, pwd_seed, qnr_bin);
/*
* Check if the candidate is a valid x-coordinate on our curve,
* and convert it from scalar to binary.
*/
is_residue = sae_is_quadradic_residue(curve, pwd_value,
qr, qnr);
l_ecc_scalar_get_data(pwd_value, x_cand, sizeof(x_cand));
/*
* If we already found the point, we overwrite x with itself.
* Otherwise, we copy the new candidate into x.
*/
util_secure_select(found, x, x_cand, x, sizeof(x));
is_odd = util_secure_select_byte(found, is_odd,
pwd_seed[31] & 0x01);
/*
* found is 0 or 0xff here and is_residue is 0 or 1. Bitwise OR
* of them (with is_residue converted to 0/0xff) handles this
* in constant time.
*/
found |= is_residue * 0xff;
memset(pwd_seed, 0, sizeof(pwd_seed));
l_ecc_scalar_free(pwd_value);
}
l_ecc_scalar_free(qr);
l_ecc_scalar_free(qnr);
l_free(dummy);
l_free(base);
if (!found) {
l_error("max PWE iterations reached!");
return NULL;
}
pwe = l_ecc_point_from_data(curve, !is_odd + 2, x, sizeof(x));
if (!pwe)
l_error("computing y failed, was x quadratic residue?");
return pwe;
}
static int sae_build_commit(struct sae_sm *sm, const uint8_t *addr1,
const uint8_t *addr2, uint8_t *commit,
size_t len, bool retry)
{
struct l_ecc_scalar *mask;
uint8_t *ptr = commit;
struct l_ecc_scalar *order;
struct ie_tlv_builder builder;
if (retry)
goto old_commit;
switch (sm->sae_type) {
case CRYPTO_SAE_HASH_TO_ELEMENT:
{
const struct l_ecc_point *pt =
sm->handshake->ecc_sae_pts[sm->group_retry];
sm->pwe = crypto_derive_sae_pwe_from_pt_ecc(addr1, addr2, pt);
break;
}
case CRYPTO_SAE_LOOPING:
sm->pwe = sae_compute_pwe(sm->curve, sm->handshake->passphrase,
addr1, addr2);
break;
}
if (!sm->pwe) {
l_error("could not compute PWE");
return -EIO;
}
sm->scalar = l_ecc_scalar_new(sm->curve, NULL, 0);
sm->rand = l_ecc_scalar_new_random(sm->curve);
mask = l_ecc_scalar_new_random(sm->curve);
order = l_ecc_curve_get_order(sm->curve);
/* commit-scalar = (rand + mask) mod r */
l_ecc_scalar_add(sm->scalar, sm->rand, mask, order);
l_ecc_scalar_free(order);
/* commit-element = inv(mask * PWE) */
sm->element = l_ecc_point_new(sm->curve);
l_ecc_point_multiply(sm->element, mask, sm->pwe);
l_ecc_point_inverse(sm->element);
l_ecc_scalar_free(mask);
/*
* Several cases require retransmitting the same commit message. The
* anti-clogging code path requires this as well as the retransmission
* timeout.
*/
old_commit:
/*
* 12.4.7.4 Encoding and decoding of SAE Commit messages
* Refer to Table 9-40 for order and Table 9-41 for presence
* of elements
*/
/* "a Transaction Sequence Number of 1" */
l_put_le16(1, ptr);
ptr += 2;
/* "a Status Code of SUCCESS or SAE_HASH_TO_ELEMENT" */
l_put_le16(sae_status_code(sm), ptr);
ptr += 2;
/* group */
l_put_le16(sm->group, ptr);
ptr += 2;
if (sm->sae_type == CRYPTO_SAE_LOOPING && sm->token) {
memcpy(ptr, sm->token, sm->token_len);
ptr += sm->token_len;
}
ptr += l_ecc_scalar_get_data(sm->scalar, ptr, L_ECC_SCALAR_MAX_BYTES);
ptr += l_ecc_point_get_data(sm->element, ptr, L_ECC_POINT_MAX_BYTES);
ie_tlv_builder_init(&builder, ptr, len - (ptr - commit));
if (sm->sae_type != CRYPTO_SAE_LOOPING && sm->rejected_groups) {
ie_tlv_builder_next(&builder, IE_TYPE_REJECTED_GROUPS);
ie_tlv_builder_set_data(&builder, sm->rejected_groups + 1,
sm->rejected_groups[0] * sizeof(uint16_t));
}
if (sm->sae_type != CRYPTO_SAE_LOOPING && sm->token) {
ie_tlv_builder_next(&builder,
IE_TYPE_ANTI_CLOGGING_TOKEN_CONTAINER);
ie_tlv_builder_set_data(&builder, sm->token, sm->token_len);
}
ie_tlv_builder_finalize(&builder, &len);
return ptr - commit + len;
}
static bool sae_send_confirm(struct sae_sm *sm)
{
uint8_t confirm[SAE_MAX_HASH_LEN];
uint8_t body[sizeof(confirm) + 6];
uint8_t *ptr = body;
ssize_t r;
/*
* confirm = CN(KCK, send-confirm, commit-scalar, COMMIT-ELEMENT,
* peer-commit-scalar, PEER-COMMIT-ELEMENT)
*/
r = sae_cn(sm, sm->sc, sm->scalar, sm->element, sm->p_scalar,
sm->p_element, confirm);
if (r < 0)
return false;
l_put_le16(2, ptr);
ptr += 2;
l_put_le16(0, ptr);
ptr += 2;
l_put_le16(sm->sc, ptr);
ptr += 2;
memcpy(ptr, confirm, r);
ptr += r;
sm->tx_auth(body, ptr - body, sm->user_data);
return true;
}
static int sae_process_commit(struct sae_sm *sm, const uint8_t *from,
const uint8_t *frame, size_t len)
{
uint8_t *ptr = (uint8_t *) frame;
unsigned int nbytes = l_ecc_curve_get_scalar_bytes(sm->curve);
enum l_checksum_type hash =
crypto_sae_hash_from_ecc_prime_len(sm->sae_type, nbytes);
size_t hash_len = l_checksum_digest_length(hash);
struct l_ecc_point *k_point;
uint8_t k[L_ECC_SCALAR_MAX_BYTES];
ssize_t klen;
const void *salt = NULL;
size_t salt_len = 0;
uint8_t keyseed[SAE_MAX_HASH_LEN];
uint8_t kck_and_pmk[SAE_MAX_HASH_LEN + 32];
uint8_t tmp[L_ECC_SCALAR_MAX_BYTES];
struct l_ecc_scalar *tmp_scalar;
struct l_ecc_scalar *order;
ptr += 2;
sm->p_scalar = l_ecc_scalar_new(sm->curve, ptr, nbytes);
if (!sm->p_scalar) {
l_error("Server sent invalid P_Scalar during commit");
return sae_reject(sm, SAE_STATE_COMMITTED,
MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP);
}
ptr += nbytes;
sm->p_element = l_ecc_point_from_data(sm->curve, L_ECC_POINT_TYPE_FULL,
ptr, nbytes * 2);
if (!sm->p_element) {
l_error("Server sent invalid P_Element during commit");
return sae_reject(sm, SAE_STATE_COMMITTED,
MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP);
}
/*
* If they match those sent as part of the protocol instance's own
* SAE Commit message, the frame shall be silently discarded (because
* it is evidence of a reflection attack) and the t0 (retransmission)
* timer shall be set.
*/
if (l_ecc_scalars_are_equal(sm->p_scalar, sm->scalar) ||
l_ecc_points_are_equal(sm->p_element, sm->element)) {
l_warn("peer scalar or element matched own, discarding frame");
return -ENOMSG;
}
sm->sc++;
/*
* K = scalar-op(rand, (element-op(scalar-op(peer-commit-scalar, PWE),
* PEER-COMMIT-ELEMENT)))
*/
k_point = l_ecc_point_new(sm->curve);
/* k_point = scalar-op(peer-commit-scalar, PWE) */
l_ecc_point_multiply(k_point, sm->p_scalar, sm->pwe);
/* k_point = element-op(k_point, PEER-COMMIT-ELEMENT) */
l_ecc_point_add(k_point, k_point, sm->p_element);
/* k_point = scalar-op(rand, k_point) */
l_ecc_point_multiply(k_point, sm->rand, k_point);
/*
* IEEE 802.11-2016 - Section 12.4.4.2.1 ECC group definition
* ECC groups make use of a mapping function, F, that maps a
* point (x, y) that satisfies the curve equation to its x-coordinate-
* i.e., if P = (x, y) then F(P) = x.
*/
klen = l_ecc_point_get_x(k_point, k, sizeof(k));
l_ecc_point_free(k_point);
if (klen < 0)
return sae_reject(sm, SAE_STATE_COMMITTED,
MMPDU_STATUS_CODE_UNSPECIFIED);
/*
* keyseed = H(salt, k)
*
* 802.11-2020 12.4.5.4:
* Hash to Element case:
* "... a salt consisting of the concatenation of the rejected groups
* from each peer's Rejected Groups element shall be
* passed to the KDF; those of the peer with the highest MAC address go
* first (if only one sent a Rejected Groups element then the salt will
* consist of that list). "
*
* Looping case:
* "...the salt shall consist of a series of octets of the value zero
* whose length equals the length of the digest of the hash function
* used to instantiate H()."
*
* NOTE: We use hkdf_extract here since it is just an hmac invocation
* and it handles the case of the zero key for us.
*/
if (sm->sae_type != CRYPTO_SAE_LOOPING && sm->rejected_groups) {
salt = sm->rejected_groups + 1;
salt_len = sm->rejected_groups[0] * sizeof(uint16_t);
}
hkdf_extract(hash, salt, salt_len, 1, keyseed, k, klen);
/*
* context = (commit-scalar + peer-commit-scalar) mod r
* Length = Q + 256
* kck_and_pmk = KDF-Hash-Length(keyseed, "SAE KCK and PMK", context)
* KCK = L(kck_and_pmk, 0, Q)
* PMK = L(kck_and_pmk, Q, 256)
*
* Q is the length of the digest of the H(), the hash function used
*/
tmp_scalar = l_ecc_scalar_new(sm->curve, NULL, 0);
order = l_ecc_curve_get_order(sm->curve);
l_ecc_scalar_add(tmp_scalar, sm->p_scalar, sm->scalar, order);
l_ecc_scalar_get_data(tmp_scalar, tmp, sizeof(tmp));
crypto_kdf(hash, keyseed, hash_len,
"SAE KCK and PMK", strlen("SAE KCK and PMK"),
tmp, nbytes, kck_and_pmk, hash_len + 32);
memcpy(sm->kck, kck_and_pmk, hash_len);
memcpy(sm->pmk, kck_and_pmk + hash_len, 32);
/*
* PMKID = L((commit-scalar + peer-commit-scalar) mod r, 0, 128)
*/
l_ecc_scalar_add(tmp_scalar, sm->scalar, sm->p_scalar, order);
l_ecc_scalar_get_data(tmp_scalar, tmp, sizeof(tmp));
l_ecc_scalar_free(order);
l_ecc_scalar_free(tmp_scalar);
/* don't set the handshakes pmkid until confirm is verified */
memcpy(sm->pmkid, tmp, 16);
if (!sae_send_confirm(sm))
return -EPROTO;
sm->state = SAE_STATE_CONFIRMED;
return 0;
}
static bool sae_verify_confirm(struct sae_sm *sm, const uint8_t *frame)
{
uint8_t check[SAE_MAX_HASH_LEN];
uint16_t rc = l_get_le16(frame);
ssize_t r;
r = sae_cn(sm, rc, sm->p_scalar, sm->p_element, sm->scalar,
sm->element, check);
if (r < 0)
return false;
if (memcmp(frame + 2, check, r))
return false;
sm->rc = rc;
return true;
}
static int sae_process_confirm(struct sae_sm *sm, const uint8_t *from,
const uint8_t *frame, size_t len)
{
const uint8_t *ptr = frame;
/*
* If processing is unsuccessful and the SAE Confirm message is not
* verified, protocol instance shall remain in Confirmed state.
*
* NOTE: We diverge from the protocol here and bail out early
*/
if (!sae_verify_confirm(sm, ptr)) {
l_error("SAE: Confirm could not be verified");
return sae_reject(sm, SAE_STATE_CONFIRMED,
MMPDU_STATUS_CODE_UNSPECIFIED);
}
/* Sc shall be set to the value 2^16 - 1 */
sm->sc = 0xffff;
handshake_state_set_pmkid(sm->handshake, sm->pmkid);
handshake_state_set_pmk(sm->handshake, sm->pmk, 32);
sm->state = SAE_STATE_ACCEPTED;
sm->tx_assoc(sm->user_data);
return 0;
}
static bool sae_send_commit(struct sae_sm *sm, bool retry)
{
struct handshake_state *hs = sm->handshake;
/* regular commit + 3x IEs (257 bytes) + 6 bytes header */
uint8_t commit[L_ECC_SCALAR_MAX_BYTES + L_ECC_POINT_MAX_BYTES + 777];
int r;
r = sae_build_commit(sm, hs->spa, hs->aa,
commit, sizeof(commit), retry);
if (r < 0)
return false;
sm->tx_auth(commit, r, sm->user_data);
return true;
}
static bool sae_assoc_timeout(struct auth_proto *ap)
{
struct sae_sm *sm = l_container_of(ap, struct sae_sm, ap);
if (sm->assoc_retry >= SAE_MAX_ASSOC_RETRY)
return false;
sm->assoc_retry++;
sm->tx_assoc(sm->user_data);
return true;
}
/*
* 802.11-2016 - Section 12.4.8.6.4
* If the Status code is ANTI_CLOGGING_TOKEN_REQUIRED, a new SAE Commit message
* shall be constructed with the Anti-Clogging Token from the received
* Authentication frame, and the commit-scalar and COMMIT-ELEMENT previously
* sent. The new SAE Commit message shall be transmitted to the peer, Sync shall
* be zeroed, and the t0 (retransmission) timer shall be set.
*/
static int sae_process_anti_clogging(struct sae_sm *sm, const uint8_t *ptr,
size_t len)
{
/*
* 802.11 doesn't talk about validating the group of the Anti-Clogging
* Request message. We assume here that the group is something that
* we would have potentially sent
*/
if (len < 2)
return -EBADMSG;
if (sae_valid_group(sm, l_get_le16(ptr)) < 0)
return -EBADMSG;
len -= 2;
ptr += 2;
/*
* 802.11-2020, Table 9-41:
* When the hash-to-element method is used to derive the PWE, the
* Anti-Clogging Token Container element is present if the
* Status Code field is ANTI_CLOGGING_TOKEN_REQUIRED
*/
if (sm->sae_type != CRYPTO_SAE_LOOPING) {
if (len < 3)
return -EBADMSG;
if (ptr[0] != IE_TYPE_EXTENSION || ptr[2] != 93 ||
ptr[1] < 2 || len < ptr[1] + 2u)
return -EBADMSG;
len = ptr[1] - 1;
ptr += 3;
}
/*
* IEEE 802.11-2016 - Section 12.4.6 Anti-clogging tokens
*
* "It is suggested that an Anti-Clogging Token not exceed 256 octets"
*
* Also ensure the token is at least 1 byte. The packet passed in will
* contain the group number, meaning the anti-clogging token length is
* going to be 2 bytes less than the passed in length. This is why we
* are checking 3 > len > 258.
*/
if (len < 1 || len > 256) {
l_error("anti-clogging token size invalid %zu", len);
return -EBADMSG;
}
l_free(sm->token);
sm->token = l_memdup(ptr, len);
sm->token_len = len;
sm->sync = 0;
sae_send_commit(sm, true);
return -EAGAIN;
}
/*
* 802.11-2016 - 12.4.8.6.3 Protocol instance behavior - Nothing state
*/
static int sae_verify_nothing(struct sae_sm *sm, uint16_t transaction,
uint16_t status, const uint8_t *frame,
size_t len)
{
/*
* TODO: This does not handle the transition from NOTHING -> CONFIRMED
* as this is only relevant to the AP or in Mesh mode which is not
* yet supported.
*/
if (transaction != SAE_STATE_COMMITTED)
return -EBADMSG;
/* frame shall be silently discarded and Del event sent */
if (status != 0)
return -EBADMSG;
if (len < 2)
return -EBADMSG;
/* reject with unsupported group */
if (l_get_le16(frame) != sm->group)
return sae_reject(sm, SAE_STATE_COMMITTED,
MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP);
return 0;
}
/*
* 802.11-2016 - 12.4.8.6.4 Protocol instance behavior - Committed state
*/
static int sae_verify_committed(struct sae_sm *sm, uint16_t transaction,
uint16_t status, const uint8_t *frame,
size_t len)
{
unsigned int skip;
struct ie_tlv_iter iter;
/*
* Upon receipt of a Con event...
* Then the protocol instance checks the value of Sync. If it
* is greater than dot11RSNASAESync, the protocol instance shall send a
* Del event to the parent process and transition back to Nothing state.
* If Sync is not greater than dot11RSNASAESync, the protocol instance
* shall increment Sync, transmit the last SAE Commit message sent to
* the peer...
*/
if (transaction == SAE_STATE_CONFIRMED) {
if (sm->sync > SAE_SYNC_MAX)
return -ETIMEDOUT;
sm->sync++;
sae_send_commit(sm, true);
return -EAGAIN;
}
if (status == MMPDU_STATUS_CODE_ANTI_CLOGGING_TOKEN_REQ)
return sae_process_anti_clogging(sm, frame, len);
if (status == MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP) {
/*
* TODO: hostapd in its current state does not include the
* group number as it should. This is a violation of the spec,
* but there isn't much we can do about it. We simply treat this
* response as if its rejecting our last commit message (which
* it most likely is). If/When this is fixed we should be
* checking that the group matches here, e.g.
*
* if (l_get_le16(frame) != sm->group)
* return false;
*
* According to 802.11 Section 12.4.8.6.4:
*
* "If the rejected group does not match the last offered group
* the protocol instance shall silently discard the message and
* set the t0 (retransmission) timer"
*/
if (len == 0)
l_warn("AP did not include group number in response!");
else if (len >= 2 && (l_get_le16(frame) != sm->group))
return -ENOMSG;
sae_rejected_groups_append(sm, L_CPU_TO_LE16(sm->group));
/*
* "If the rejected group matches the last offered group, the
* protocol instance shall choose a different group and generate
* the PWE and the secret values according to 12.4.5.2; it then
* generates and transmits a new SAE Commit message to the peer,
* zeros Sync, sets the t0 (retransmission) timer, and remains
* in Committed state"
*/
if (sae_choose_next_group(sm) < 0) {
/*
* "If there are no other groups to choose, the protocol
* instance shall send a Del event to the parent process
* and transitions back to Nothing state"
*/
sm->state = SAE_STATE_NOTHING;
goto reject_unsupp_group;
}
sm->sync = 0;
sae_send_commit(sm, false);
return -EAGAIN;
}
/*
* If the Status is some other nonzero value, the frame shall be
* silently discarded and the t0 (retransmission) timer shall be set.
*/
if (status != 0 && status != MMPDU_STATUS_CODE_SAE_HASH_TO_ELEMENT)
return -ENOMSG;
if (status != sae_status_code(sm))
return -EBADMSG;
if (len < 2)
return -EBADMSG;
if (l_get_le16(frame) != sm->group) {
l_error("SAE: Peer tried to change group -- Reject");
goto reject_unsupp_group;
}
len -= 2;
frame += 2;
skip = l_ecc_curve_get_scalar_bytes(sm->curve) * 3;
if (len < skip)
return -EBADMSG;
/* If H2E isn't being used, there should be no IEs in use */
if (status == 0)
return 0;
len -= skip;
frame += skip;
ie_tlv_iter_init(&iter, frame, len);
while (ie_tlv_iter_next(&iter)) {
switch (ie_tlv_iter_get_tag(&iter)) {
/*
* If the peer's SAE Commit message contains a Rejected Groups
* element, the list of rejected groups shall be checked to
* ensure that all of the groups in the list are groups that
* would be rejected. If any groups in the list would not be
* rejected then processing of the SAE Commit message
* terminates and the STA shall reject the peer's
* authentication.
*
* NOTE: We currently only support the Initiator role, and so
* do not reject any groups. We should never receive this
* element
*/
case IE_TYPE_REJECTED_GROUPS:
l_error("SAE: Unexpected Rejected Groups IE");
return sae_reject(sm, SAE_STATE_COMMITTED,
MMPDU_STATUS_CODE_UNSPECIFIED);
/* We don't request tokens, so we shouldn't get any */
case IE_TYPE_ANTI_CLOGGING_TOKEN_CONTAINER:
l_error("SAE: Unexpected Anti-Clogging Container IE");
return sae_reject(sm, SAE_STATE_COMMITTED,
MMPDU_STATUS_CODE_UNSPECIFIED);
}
}
return 0;
reject_unsupp_group:
return sae_reject(sm, SAE_STATE_COMMITTED,
MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP);
}
/*
* 802.11-2016 - 12.4.8.6.5 Protocol instance behavior - Confirmed state
*/
static int sae_verify_confirmed(struct sae_sm *sm, uint16_t trans,
uint16_t status, const uint8_t *frame,
size_t len)
{
if (trans == SAE_STATE_CONFIRMED) {
enum l_checksum_type hash =
crypto_sae_hash_from_ecc_prime_len(sm->sae_type,
l_ecc_curve_get_scalar_bytes(sm->curve));
size_t hash_len = l_checksum_digest_length(hash);
/* Most likely the password is wrong */
if (status == MMPDU_STATUS_CODE_UNSPECIFIED && len == 0)
return -ENOKEY;
if (status != MMPDU_STATUS_CODE_SUCCESS)
return -EPROTO;
if (len < hash_len + 2) {
l_error("SAE: Confirm packet too short");
return -EBADMSG;
}
return 0;
}
/*
* Upon receipt of a Com event, the t0 (retransmission) timer shall be
* canceled. If the Status is nonzero, the frame shall be silently
* discarded, the t0 (retransmission) timer set, and the protocol
* instance shall remain in the Confirmed state.
*/
if (status != 0)
return -ENOMSG;
/*
* If Sync is greater than dot11RSNASAESync, the protocol instance
* shall send the parent process a Del event and transitions back to
* Nothing state.
*/
if (sm->sync > SAE_SYNC_MAX)
return -ETIMEDOUT;
if (len < 2)
return -EBADMSG;
/* frame shall be silently discarded */
if (l_get_le16(frame) != sm->group)
return -EBADMSG;
/*
* the protocol instance shall increment Sync, increment Sc, and
* transmit its Commit and Confirm (with the new Sc value) messages.
*/
sm->sync++;
sm->sc++;
sae_send_commit(sm, true);
if (!sae_send_confirm(sm))
return -EPROTO;
return -EAGAIN;
}
/*
* 802.11-2016 - 12.4.8.6.6 Protocol instance behavior - Accepted state
*/
static int sae_verify_accepted(struct sae_sm *sm, uint16_t trans,
uint16_t status, const uint8_t *frame,
size_t len)
{
uint16_t sc;
/* spec does not specify what to do here, so print and discard */
if (trans != SAE_STATE_CONFIRMED) {
l_error("received transaction %u in accepted state", trans);
return -EBADMSG;
}
if (sm->sync > SAE_SYNC_MAX)
return -ETIMEDOUT;
if (len < 2)
return -EBADMSG;
sc = l_get_le16(frame);
/*
* ... the value of send-confirm shall be checked. If the value is not
* greater than Rc or is equal to 2^16 - 1, the received frame shall be
* silently discarded.
*/
if (sc <= sm->rc || sc == 0xffff)
return -EBADMSG;
/*
* If the verification fails, the received frame shall be silently
* discarded.
*/
if (!sae_verify_confirm(sm, frame))
return -EBADMSG;
/*
* If the verification succeeds, the Rc variable shall be set to the
* send-confirm portion of the frame, the Sync shall be incremented and
* a new SAE Confirm message shall be constructed (with Sc set to
* 2^16 - 1) and sent to the peer.
*/
sm->sync++;
sm->sc = 0xffff;
if (!sae_send_confirm(sm))
return -EPROTO;
return -EAGAIN;
}
static int sae_verify_packet(struct sae_sm *sm, uint16_t trans,
uint16_t status, const uint8_t *frame,
size_t len)
{
if (trans != SAE_STATE_COMMITTED && trans != SAE_STATE_CONFIRMED)
return -EBADMSG;
switch (sm->state) {
case SAE_STATE_NOTHING:
return sae_verify_nothing(sm, trans, status, frame, len);
case SAE_STATE_COMMITTED:
return sae_verify_committed(sm, trans, status, frame, len);
case SAE_STATE_CONFIRMED:
return sae_verify_confirmed(sm, trans, status, frame, len);
case SAE_STATE_ACCEPTED:
return sae_verify_accepted(sm, trans, status, frame, len);
}
/* should never get here */
return -EPROTO;
}
static int sae_rx_authenticate(struct auth_proto *ap,
const uint8_t *frame, size_t len)
{
struct sae_sm *sm = l_container_of(ap, struct sae_sm, ap);
const struct mmpdu_header *hdr = (const struct mmpdu_header *) frame;
const struct mmpdu_authentication *auth = mmpdu_body(hdr);
int ret;
len -= mmpdu_header_len(hdr);
ret = sae_verify_packet(sm, L_LE16_TO_CPU(auth->transaction_sequence),
L_LE16_TO_CPU(auth->status),
auth->ies, len - 6);
if (ret != 0)
return ret;
switch (L_LE16_TO_CPU(auth->transaction_sequence)) {
case SAE_STATE_COMMITTED:
return sae_process_commit(sm, hdr->address_2, auth->ies,
len - 6);
case SAE_STATE_CONFIRMED:
return sae_process_confirm(sm, hdr->address_2, auth->ies,
len - 6);
default:
l_error("invalid transaction sequence %u",
L_LE16_TO_CPU(auth->transaction_sequence));
}
/* should never get here */
return -EPROTO;
}
static int sae_rx_associate(struct auth_proto *ap, const uint8_t *frame,
size_t len)
{
const struct mmpdu_header *mpdu = (const struct mmpdu_header *)frame;
const struct mmpdu_association_response *body = mmpdu_body(mpdu);
if (body->status_code != 0)
return -EPROTO;
return 0;
}
static bool sae_start(struct auth_proto *ap)
{
struct sae_sm *sm = l_container_of(ap, struct sae_sm, ap);
if (sm->handshake->authenticator)
memcpy(sm->peer, sm->handshake->spa, 6);
else
memcpy(sm->peer, sm->handshake->aa, 6);
if (sm->sae_type == CRYPTO_SAE_LOOPING && !sm->handshake->passphrase) {
l_error("SAE: No passphrase set");
return false;
}
if (sae_choose_next_group(sm) < 0)
return false;
sm->state = SAE_STATE_COMMITTED;
return sae_send_commit(sm, false);
}
bool sae_sm_is_h2e(struct auth_proto *ap)
{
struct sae_sm *sm = l_container_of(ap, struct sae_sm, ap);
return sm->sae_type != CRYPTO_SAE_LOOPING;
}
static void sae_free(struct auth_proto *ap)
{
struct sae_sm *sm = l_container_of(ap, struct sae_sm, ap);
sae_reset_state(sm);
l_free(sm->token);
sm->token = NULL;
if (sm->rejected_groups)
free(sm->rejected_groups);
/* zero out whole structure, including keys */
explicit_bzero(sm, sizeof(struct sae_sm));
l_free(sm);
}
struct auth_proto *sae_sm_new(struct handshake_state *hs,
sae_tx_authenticate_func_t tx_auth,
sae_tx_associate_func_t tx_assoc,
void *user_data)
{
struct sae_sm *sm;
const void *rsnxe;
sm = l_new(struct sae_sm, 1);
sm->group_retry = -1;
sm->tx_auth = tx_auth;
sm->tx_assoc = tx_assoc;
sm->user_data = user_data;
sm->handshake = hs;
sm->state = SAE_STATE_NOTHING;
sm->ap.start = sae_start;
sm->ap.free = sae_free;
sm->ap.rx_authenticate = sae_rx_authenticate;
sm->ap.rx_associate = sae_rx_associate;
sm->ap.assoc_timeout = sae_assoc_timeout;
rsnxe = hs->authenticator ? hs->supplicant_rsnxe :
hs->authenticator_rsnxe;
if (ie_rsnxe_capable(rsnxe, IE_RSNX_SAE_H2E) && hs->ecc_sae_pts) {
l_debug("Using SAE H2E");
sm->sae_type = CRYPTO_SAE_HASH_TO_ELEMENT;
} else {
l_debug("Using SAE Hunting and Pecking");
sm->sae_type = CRYPTO_SAE_LOOPING;
}
return &sm->ap;
}
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