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>

hostapd/Android.mk

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

hostapd/Makefile

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

src/ap/ieee802_11.c

@@ -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;
-
+	sae_write_commit(sta->sae, buf);
-	wpabuf_put_le16(buf, 19); /* Finite Cyclic Group */
-	/* TODO: Anti-Clogging Token (if requested) */
-	/* TODO: Scalar */
-	/* TODO: Element */
 
 	return buf;
 }

src/common/sae.c

@@ -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);
+}

src/common/sae.h

@@ -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 */

wpa_supplicant/Android.mk

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

wpa_supplicant/Makefile

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

wpa_supplicant/sme.c

@@ -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 */
+	sae_write_commit(&wpa_s->sme.sae, buf);
-	/* TODO: Anti-Clogging Token (if requested) */
-	/* TODO: Scalar */
-	/* TODO: Element */
 
 	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)