SAE: Add generation of the commit message fields

This adds derivation of PWE and the needed commit values so that the
full SAE commit message can be built.

Signed-hostap: Jouni Malinen <j@w1.fi>
This commit is contained in:
Jouni Malinen 2012-12-30 22:06:11 +02:00
parent 750efe6ea6
commit 8e31e9550a
8 changed files with 357 additions and 14 deletions

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@ -202,6 +202,7 @@ endif
ifdef CONFIG_SAE
L_CFLAGS += -DCONFIG_SAE
OBJS += src/common/sae.c
endif
ifdef CONFIG_IEEE80211N

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@ -174,6 +174,7 @@ endif
ifdef CONFIG_SAE
CFLAGS += -DCONFIG_SAE
OBJS += ../src/common/sae.o
endif
ifdef CONFIG_WNM

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@ -323,14 +323,18 @@ static struct wpabuf * auth_build_sae_commit(struct hostapd_data *hapd,
{
struct wpabuf *buf;
buf = wpabuf_alloc(2);
if (sae_prepare_commit(hapd->own_addr, sta->addr,
(u8 *) hapd->conf->ssid.wpa_passphrase,
os_strlen(hapd->conf->ssid.wpa_passphrase),
sta->sae) < 0) {
wpa_printf(MSG_DEBUG, "SAE: Could not pick PWE");
return NULL;
}
buf = wpabuf_alloc(SAE_COMMIT_MAX_LEN);
if (buf == NULL)
return NULL;
wpabuf_put_le16(buf, 19); /* Finite Cyclic Group */
/* TODO: Anti-Clogging Token (if requested) */
/* TODO: Scalar */
/* TODO: Element */
sae_write_commit(sta->sae, buf);
return buf;
}

311
src/common/sae.c Normal file
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@ -0,0 +1,311 @@
/*
* Simultaneous authentication of equals
* Copyright (c) 2012, Jouni Malinen <j@w1.fi>
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
*/
#include "includes.h"
/* TODO: move OpenSSL dependencies into crypto/crypto_openssl.c */
#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/obj_mac.h>
#include "common.h"
#include "crypto/sha256.h"
#include "crypto/random.h"
#include "sae.h"
static const u8 group19_prime[] = {
0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x01,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
};
static const u8 group19_order[] = {
0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xBC, 0xE6, 0xFA, 0xAD, 0xA7, 0x17, 0x9E, 0x84,
0xF3, 0xB9, 0xCA, 0xC2, 0xFC, 0x63, 0x25, 0x51
};
static int val_zero_or_one(const u8 *val, size_t len)
{
size_t i;
for (i = 0; i < len - 1; i++) {
if (val[i])
return 0;
}
return val[len - 1] <= 1;
}
static int sae_get_rand(u8 *val)
{
int iter = 0;
do {
if (random_get_bytes(val, sizeof(group19_prime)) < 0)
return -1;
if (iter++ > 100)
return -1;
} while (os_memcmp(val, group19_order, sizeof(group19_prime)) >= 0 ||
val_zero_or_one(val, sizeof(group19_prime)));
return 0;
}
static void sae_bn_to_bin(const BIGNUM *bn, u8 *bin, size_t len)
{
int offset = len - BN_num_bytes(bn);
os_memset(bin, 0, offset);
BN_bn2bin(bn, bin + offset);
}
static int sae_ec_point_to_bin(BN_CTX *bnctx, EC_GROUP *group, EC_POINT *point,
u8 *bin)
{
BIGNUM *x, *y;
int ret = -1;
x = BN_new();
y = BN_new();
if (x && y &&
EC_POINT_get_affine_coordinates_GFp(group, point, x, y, bnctx)) {
sae_bn_to_bin(x, bin, 32);
sae_bn_to_bin(y, bin + 32, 32);
ret = 0;
}
BN_free(x);
BN_free(y);
return ret;
}
static void sae_pwd_seed_key(const u8 *addr1, const u8 *addr2, u8 *key)
{
wpa_printf(MSG_DEBUG, "SAE: PWE derivation - addr1=" MACSTR
" addr2=" MACSTR, MAC2STR(addr1), MAC2STR(addr2));
if (os_memcmp(addr1, addr2, ETH_ALEN) > 0) {
os_memcpy(key, addr1, ETH_ALEN);
os_memcpy(key + ETH_ALEN, addr2, ETH_ALEN);
} else {
os_memcpy(key, addr2, ETH_ALEN);
os_memcpy(key + ETH_ALEN, addr1, ETH_ALEN);
}
}
static int sae_test_pwd_seed(BN_CTX *bnctx, EC_GROUP *group, const u8 *pwd_seed,
EC_POINT *pwe, u8 *pwe_bin)
{
u8 pwd_value[32];
BIGNUM *x;
int y_bit;
wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-seed", pwd_seed, 32);
/* pwd-value = KDF-z(pwd-seed, "SAE Hunting and Pecking", p) */
sha256_prf(pwd_seed, 32, "SAE Hunting and Pecking",
group19_prime, sizeof(group19_prime),
pwd_value, sizeof(pwd_value));
wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-value",
pwd_value, sizeof(pwd_value));
if (os_memcmp(pwd_value, group19_prime, sizeof(group19_prime)) >= 0)
return 0;
y_bit = pwd_seed[SHA256_MAC_LEN - 1] & 0x01;
x = BN_bin2bn(pwd_value, sizeof(pwd_value), NULL);
if (x == NULL)
return -1;
if (!EC_POINT_set_compressed_coordinates_GFp(group, pwe, x, y_bit,
bnctx) ||
!EC_POINT_is_on_curve(group, pwe, bnctx)) {
BN_free(x);
wpa_printf(MSG_DEBUG, "SAE: No solution found");
return 0;
}
BN_free(x);
wpa_printf(MSG_DEBUG, "SAE: PWE found");
if (sae_ec_point_to_bin(bnctx, group, pwe, pwe_bin) < 0)
return -1;
wpa_hexdump_key(MSG_DEBUG, "SAE: PWE x", pwe_bin, 32);
wpa_hexdump_key(MSG_DEBUG, "SAE: PWE y", pwe_bin + 32, 32);
return 1;
}
static int sae_derive_pwe(BN_CTX *bnctx, EC_GROUP *group, const u8 *addr1,
const u8 *addr2, const u8 *password,
size_t password_len, EC_POINT *pwe, u8 *pwe_bin)
{
u8 counter, k = 4;
u8 addrs[2 * ETH_ALEN];
const u8 *addr[2];
size_t len[2];
int found = 0;
EC_POINT *pwe_tmp;
u8 pwe_bin_tmp[2 * 32];
pwe_tmp = EC_POINT_new(group);
if (pwe_tmp == NULL)
return -1;
wpa_hexdump_ascii_key(MSG_DEBUG, "SAE: password",
password, password_len);
/*
* H(salt, ikm) = HMAC-SHA256(salt, ikm)
* pwd-seed = H(MAX(STA-A-MAC, STA-B-MAC) || MIN(STA-A-MAC, STA-B-MAC),
* password || counter)
*/
sae_pwd_seed_key(addr1, addr2, addrs);
addr[0] = password;
len[0] = password_len;
addr[1] = &counter;
len[1] = sizeof(counter);
/*
* Continue for at least k iterations to protect against side-channel
* attacks that attempt to determine the number of iterations required
* in the loop.
*/
for (counter = 1; counter < k || !found; counter++) {
u8 pwd_seed[SHA256_MAC_LEN];
int res;
wpa_printf(MSG_DEBUG, "SAE: counter = %u", counter);
if (hmac_sha256_vector(addrs, sizeof(addrs), 2, addr, len,
pwd_seed) < 0)
break;
res = sae_test_pwd_seed(bnctx, group, pwd_seed,
found ? pwe_tmp : pwe,
found ? pwe_bin_tmp : pwe_bin);
if (res < 0)
break;
if (res == 0)
continue;
if (found) {
wpa_printf(MSG_DEBUG, "SAE: Ignore this PWE (one was "
"already selected)");
} else {
wpa_printf(MSG_DEBUG, "SAE: Use this PWE");
found = 1;
}
if (counter > 200) {
/* This should not happen in practice */
wpa_printf(MSG_DEBUG, "SAE: Failed to derive PWE");
break;
}
}
EC_POINT_clear_free(pwe_tmp);
return found ? 0 : -1;
}
static int sae_derive_commit(struct sae_data *sae, BN_CTX *bnctx,
EC_GROUP *group, EC_POINT *pwe)
{
BIGNUM *x, *bn_rand, *bn_mask, *order;
EC_POINT *elem;
u8 mask[32];
int ret = -1;
if (sae_get_rand(sae->sae_rand) < 0 || sae_get_rand(mask) < 0)
return -1;
wpa_hexdump_key(MSG_DEBUG, "SAE: rand",
sae->sae_rand, sizeof(sae->sae_rand));
wpa_hexdump_key(MSG_DEBUG, "SAE: mask", mask, sizeof(mask));
x = BN_new();
bn_rand = BN_bin2bn(sae->sae_rand, 32, NULL);
bn_mask = BN_bin2bn(mask, sizeof(mask), NULL);
order = BN_bin2bn(group19_order, sizeof(group19_order), NULL);
elem = EC_POINT_new(group);
if (x == NULL || bn_rand == NULL || bn_mask == NULL || order == NULL ||
elem == NULL)
goto fail;
/* commit-scalar = (rand + mask) modulo r */
BN_add(x, bn_rand, bn_mask);
BN_mod(x, x, order, bnctx);
sae_bn_to_bin(x, sae->own_commit_scalar, 32);
wpa_hexdump(MSG_DEBUG, "SAE: commit-scalar",
sae->own_commit_scalar, 32);
/* COMMIT-ELEMENT = inverse(scalar-op(mask, PWE)) */
if (!EC_POINT_mul(group, elem, NULL, pwe, bn_mask, bnctx) ||
!EC_POINT_invert(group, elem, bnctx) ||
sae_ec_point_to_bin(bnctx, group, elem, sae->own_commit_element) <
0)
goto fail;
wpa_hexdump(MSG_DEBUG, "SAE: commit-element x",
sae->own_commit_element, 32);
wpa_hexdump(MSG_DEBUG, "SAE: commit-element y",
sae->own_commit_element + 32, 32);
ret = 0;
fail:
EC_POINT_free(elem);
BN_free(order);
BN_clear_free(bn_mask);
os_memset(mask, 0, sizeof(mask));
BN_clear_free(bn_rand);
BN_clear_free(x);
return ret;
}
int sae_prepare_commit(const u8 *addr1, const u8 *addr2,
const u8 *password, size_t password_len,
struct sae_data *sae)
{
BN_CTX *bnctx;
EC_POINT *pwe;
EC_GROUP *group;
int ret = 0;
bnctx = BN_CTX_new();
group = EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1);
pwe = EC_POINT_new(group);
if (bnctx == NULL || group == NULL || pwe == NULL ||
sae_derive_pwe(bnctx, group, addr1, addr2, password, password_len,
pwe, sae->pwe) < 0 ||
sae_derive_commit(sae, bnctx, group, pwe) < 0)
ret = -1;
EC_POINT_clear_free(pwe);
EC_GROUP_free(group);
BN_CTX_free(bnctx);
return ret;
}
void sae_write_commit(struct sae_data *sae, struct wpabuf *buf)
{
wpabuf_put_le16(buf, 19); /* Finite Cyclic Group */
/* TODO: Anti-Clogging Token (if requested) */
wpabuf_put_data(buf, sae->own_commit_scalar, 32);
wpabuf_put_data(buf, sae->own_commit_element, 2 * 32);
}

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@ -9,9 +9,20 @@
#ifndef SAE_H
#define SAE_H
#define SAE_COMMIT_MAX_LEN (2 + 3 * 32)
struct sae_data {
enum { SAE_INIT, SAE_COMMIT, SAE_CONFIRM } state;
u16 send_confirm;
u8 own_commit_scalar[32];
u8 own_commit_element[2 * 32];
u8 pwe[2 * 32];
u8 sae_rand[32];
};
int sae_prepare_commit(const u8 *addr1, const u8 *addr2,
const u8 *password, size_t password_len,
struct sae_data *sae);
void sae_write_commit(struct sae_data *sae, struct wpabuf *buf);
#endif /* SAE_H */

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@ -181,6 +181,7 @@ endif
ifdef CONFIG_SAE
L_CFLAGS += -DCONFIG_SAE
OBJS += src/common/sae.c
endif
ifdef CONFIG_TDLS

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@ -174,6 +174,7 @@ endif
ifdef CONFIG_SAE
CFLAGS += -DCONFIG_SAE
OBJS += ../src/common/sae.o
endif
ifdef CONFIG_WNM

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@ -1,6 +1,6 @@
/*
* wpa_supplicant - SME
* Copyright (c) 2009-2010, Jouni Malinen <j@w1.fi>
* Copyright (c) 2009-2012, Jouni Malinen <j@w1.fi>
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
@ -42,20 +42,32 @@ static void sme_stop_sa_query(struct wpa_supplicant *wpa_s);
#ifdef CONFIG_SAE
static struct wpabuf * sme_auth_build_sae_commit(struct wpa_supplicant *wpa_s)
static struct wpabuf * sme_auth_build_sae_commit(struct wpa_supplicant *wpa_s,
struct wpa_ssid *ssid,
const u8 *bssid)
{
struct wpabuf *buf;
buf = wpabuf_alloc(4 + 2);
if (ssid->passphrase == NULL) {
wpa_printf(MSG_DEBUG, "SAE: No password available");
return NULL;
}
if (sae_prepare_commit(wpa_s->own_addr, bssid,
(u8 *) ssid->passphrase,
os_strlen(ssid->passphrase),
&wpa_s->sme.sae) < 0) {
wpa_printf(MSG_DEBUG, "SAE: Could not pick PWE");
return NULL;
}
buf = wpabuf_alloc(4 + SAE_COMMIT_MAX_LEN);
if (buf == NULL)
return NULL;
wpabuf_put_le16(buf, 1); /* Transaction seq# */
wpabuf_put_le16(buf, WLAN_STATUS_SUCCESS);
wpabuf_put_le16(buf, 19); /* Finite Cyclic Group */
/* TODO: Anti-Clogging Token (if requested) */
/* TODO: Scalar */
/* TODO: Element */
sae_write_commit(&wpa_s->sme.sae, buf);
return buf;
}
@ -326,7 +338,8 @@ static void sme_send_authentication(struct wpa_supplicant *wpa_s,
#ifdef CONFIG_SAE
if (params.auth_alg == WPA_AUTH_ALG_SAE) {
if (start)
resp = sme_auth_build_sae_commit(wpa_s);
resp = sme_auth_build_sae_commit(wpa_s, ssid,
bss->bssid);
else
resp = sme_auth_build_sae_confirm(wpa_s);
if (resp == NULL)