SAE: Add support for FFC groups

This allows FFC groups to be used with SAE. Though, these groups are not
included in the default sae_groups value based on what is available
since the FFC groups have the additional requirement of using a safe
prime with the current implementation (or specification of the group
order).

Signed-hostap: Jouni Malinen <j@w1.fi>

diff --git a/hostapd/Android.mk b/hostapd/Android.mk
index 7c974d7..89dbb51 100644 (file)
--- a/hostapd/Android.mk
+++ b/hostapd/Android.mk
@@ -204,6 +204,7 @@ ifdef CONFIG_SAE
 L_CFLAGS += -DCONFIG_SAE
 OBJS += src/common/sae.c
 NEED_ECC=y
+NEED_DH_GROUPS=y
 endif
 
 ifdef CONFIG_IEEE80211N

diff --git a/hostapd/Makefile b/hostapd/Makefile
index 88b1b0a..8404e0c 100644 (file)
--- a/hostapd/Makefile
+++ b/hostapd/Makefile
@@ -176,6 +176,7 @@ ifdef CONFIG_SAE
 CFLAGS += -DCONFIG_SAE
 OBJS += ../src/common/sae.o
 NEED_ECC=y
+NEED_DH_GROUPS=y
 endif
 
 ifdef CONFIG_WNM

diff --git a/src/common/sae.c b/src/common/sae.c
index d5e5e48..b7da54d 100644 (file)
--- a/src/common/sae.c
+++ b/src/common/sae.c
@@ -12,23 +12,58 @@
 #include "crypto/crypto.h"
 #include "crypto/sha256.h"
 #include "crypto/random.h"
+#include "crypto/dh_groups.h"
 #include "ieee802_11_defs.h"
 #include "sae.h"
 
 
 int sae_set_group(struct sae_data *sae, int group)
 {
-       crypto_ec_deinit(sae->ec);
+       sae_clear_data(sae);
+
+       /* First, check if this is an ECC group */
        sae->ec = crypto_ec_init(group);
-       if (!sae->ec)
-               return -1;
+       if (sae->ec) {
+               sae->group = group;
+               sae->prime_len = crypto_ec_prime_len(sae->ec);
+               sae->prime = crypto_ec_get_prime(sae->ec);
+               sae->order = crypto_ec_get_order(sae->ec);
+               return 0;
+       }
 
-       sae->group = group;
-       sae->prime_len = crypto_ec_prime_len(sae->ec);
-       sae->prime = crypto_ec_get_prime(sae->ec);
-       sae->order = crypto_ec_get_order(sae->ec);
+       /* Not an ECC group, check FFC */
+       sae->dh = dh_groups_get(group);
+       if (sae->dh) {
+               sae->group = group;
+               sae->prime_len = sae->dh->prime_len;
+               if (sae->prime_len > SAE_MAX_PRIME_LEN) {
+                       sae_clear_data(sae);
+                       return -1;
+               }
 
-       return 0;
+               sae->prime_buf = crypto_bignum_init_set(sae->dh->prime,
+                                                       sae->prime_len);
+               if (sae->prime_buf == NULL) {
+                       sae_clear_data(sae);
+                       return -1;
+               }
+               sae->prime = sae->prime_buf;
+
+               /* Assume r = (p-1)/2 for this group */
+               sae->safe_prime = 1;
+               sae->order_buf = crypto_bignum_init();
+               if (sae->order_buf == NULL ||
+                   crypto_bignum_rshift(sae->prime, 1, sae->order_buf) < 0) {
+                       sae_clear_data(sae);
+                       return -1;
+               }
+               sae->order = sae->order_buf;
+
+               return 0;
+       }
+
+       /* Unsupported group */
+       return -1;
 }
 
 
@@ -37,10 +72,25 @@ void sae_clear_data(struct sae_data *sae)
        if (sae == NULL)
                return;
        crypto_ec_deinit(sae->ec);
+       crypto_bignum_deinit(sae->prime_buf, 0);
+       crypto_bignum_deinit(sae->order_buf, 0);
        os_memset(sae, 0, sizeof(*sae));
 }
 
 
+static int val_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 val_zero_or_one(const u8 *val, size_t len)
 {
        size_t i;
@@ -115,6 +165,27 @@ static struct crypto_bignum * sae_get_rand_and_mask(struct sae_data *sae)
 }
 
 
+static struct crypto_bignum * sae_get_rand_and_mask_dh(struct sae_data *sae)
+{
+       u8 mask[SAE_MAX_PRIME_LEN], order[SAE_MAX_PRIME_LEN];
+       struct crypto_bignum *bn;
+       size_t prime_len_bits = sae->prime_len * 8;
+
+       if (crypto_bignum_to_bin(sae->order, order, sizeof(order),
+                                sae->prime_len) < 0 ||
+           sae_get_rand(order, prime_len_bits, sae->sae_rand) < 0 ||
+           sae_get_rand(order, prime_len_bits, mask) < 0)
+               return NULL;
+
+       wpa_hexdump_key(MSG_DEBUG, "SAE: rand",
+                       sae->sae_rand, sae->prime_len);
+       wpa_hexdump_key(MSG_DEBUG, "SAE: mask", mask, sae->prime_len);
+       bn = crypto_bignum_init_set(mask, sae->prime_len);
+       os_memset(mask, 0, sizeof(mask));
+       return bn;
+}
+
+
 static void sae_pwd_seed_key(const u8 *addr1, const u8 *addr2, u8 *key)
 {
        wpa_printf(MSG_DEBUG, "SAE: PWE derivation - addr1=" MACSTR
@@ -304,9 +375,9 @@ fail:
 }
 
 
-int sae_prepare_commit(const u8 *addr1, const u8 *addr2,
-                      const u8 *password, size_t password_len,
-                      struct sae_data *sae)
+static int sae_prepare_commit_ec(const u8 *addr1, const u8 *addr2,
+                                const u8 *password, size_t password_len,
+                                struct sae_data *sae)
 {
        struct crypto_ec_point *pwe;
        int ret = 0;
@@ -324,6 +395,224 @@ int sae_prepare_commit(const u8 *addr1, const u8 *addr2,
 }
 
 
+static int sae_test_pwd_seed_dh(struct sae_data *sae, const u8 *pwd_seed,
+                               struct crypto_bignum *pwe)
+{
+       u8 pwd_value[SAE_MAX_PRIME_LEN];
+       size_t bits = sae->prime_len * 8;
+       u8 exp[1];
+       struct crypto_bignum *a, *b;
+       int res;
+
+       wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-seed", pwd_seed, SHA256_MAC_LEN);
+
+       /* pwd-value = KDF-z(pwd-seed, "SAE Hunting and Pecking", p) */
+       sha256_prf_bits(pwd_seed, SHA256_MAC_LEN, "SAE Hunting and Pecking",
+                       sae->dh->prime, sae->prime_len, pwd_value, bits);
+       if (bits % 8)
+               buf_shift_right(pwd_value, sizeof(pwd_value), 8 - bits % 8);
+       wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-value", pwd_value, sae->prime_len);
+
+       if (os_memcmp(pwd_value, sae->dh->prime, sae->prime_len) >= 0) {
+               wpa_printf(MSG_DEBUG, "SAE: pwd-value >= p");
+               return 0;
+       }
+
+       /* PWE = pwd-value^((p-1)/r) modulo p */
+
+       a = crypto_bignum_init_set(pwd_value, sae->prime_len);
+
+       if (sae->safe_prime) {
+               /*
+                * r = (p-1)/2 for the group used here, so this becomes:
+                * PWE = pwd-value^2 modulo p
+                */
+               exp[0] = 2;
+               b = crypto_bignum_init_set(exp, sizeof(exp));
+               if (a == NULL || b == NULL)
+                       res = -1;
+               else
+                       res = crypto_bignum_exptmod(a, b, sae->prime, pwe);
+       } else {
+               struct crypto_bignum *tmp;
+
+               exp[0] = 1;
+               b = crypto_bignum_init_set(exp, sizeof(exp));
+               tmp = crypto_bignum_init();
+               if (a == NULL || b == NULL || tmp == NULL ||
+                   crypto_bignum_sub(sae->prime, b, tmp) < 0 ||
+                   crypto_bignum_div(tmp, sae->order, b) < 0)
+                       res = -1;
+               else
+                       res = crypto_bignum_exptmod(a, b, sae->prime, pwe);
+               crypto_bignum_deinit(tmp, 0);
+       }
+
+       crypto_bignum_deinit(a, 0);
+       crypto_bignum_deinit(b, 0);
+
+       if (res < 0) {
+               wpa_printf(MSG_DEBUG, "SAE: Failed to calculate PWE");
+               return -1;
+       }
+
+       res = crypto_bignum_to_bin(pwe, sae->pwe, sizeof(sae->pwe),
+                                  sae->prime_len);
+       if (res < 0) {
+               wpa_printf(MSG_DEBUG, "SAE: Not room for PWE");
+               return -1;
+       }
+       wpa_hexdump_key(MSG_DEBUG, "SAE: PWE candidate", sae->pwe, res);
+
+       /* if (PWE > 1) --> found */
+       if (val_zero_or_one(sae->pwe, sae->prime_len)) {
+               wpa_printf(MSG_DEBUG, "SAE: PWE <= 1");
+               return 0;
+       }
+
+       wpa_printf(MSG_DEBUG, "SAE: PWE found");
+       return 1;
+}
+
+
+static int sae_derive_pwe_dh(struct sae_data *sae, const u8 *addr1,
+                            const u8 *addr2, const u8 *password,
+                            size_t password_len, struct crypto_bignum *pwe)
+{
+       u8 counter;
+       u8 addrs[2 * ETH_ALEN];
+       const u8 *addr[2];
+       size_t len[2];
+       int found = 0;
+
+       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);
+
+       for (counter = 1; !found; counter++) {
+               u8 pwd_seed[SHA256_MAC_LEN];
+               int res;
+
+               if (counter > 200) {
+                       /* This should not happen in practice */
+                       wpa_printf(MSG_DEBUG, "SAE: Failed to derive PWE");
+                       break;
+               }
+
+               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_dh(sae, pwd_seed, pwe);
+               if (res < 0)
+                       break;
+               if (res > 0) {
+                       wpa_printf(MSG_DEBUG, "SAE: Use this PWE");
+                       found = 1;
+               }
+       }
+
+       return found ? 0 : -1;
+}
+
+
+static int sae_derive_commit_dh(struct sae_data *sae, struct crypto_bignum *pwe)
+{
+       struct crypto_bignum *x, *bn_rand, *mask, *elem;
+       int ret = -1;
+
+       mask = sae_get_rand_and_mask_dh(sae);
+       if (mask == NULL) {
+               wpa_printf(MSG_DEBUG, "SAE: Could not get rand/mask");
+               return -1;
+       }
+
+       x = crypto_bignum_init();
+       bn_rand = crypto_bignum_init_set(sae->sae_rand, sae->prime_len);
+       elem = crypto_bignum_init();
+       if (x == NULL || bn_rand == NULL || elem == NULL)
+               goto fail;
+
+       /* commit-scalar = (rand + mask) modulo r */
+       crypto_bignum_add(bn_rand, mask, x);
+       crypto_bignum_mod(x, sae->order, x);
+       crypto_bignum_to_bin(x, sae->own_commit_scalar,
+                            sizeof(sae->own_commit_scalar), sae->prime_len);
+       wpa_hexdump(MSG_DEBUG, "SAE: commit-scalar",
+                   sae->own_commit_scalar, sae->prime_len);
+
+       /* COMMIT-ELEMENT = inverse(scalar-op(mask, PWE)) */
+       if (crypto_bignum_exptmod(pwe, mask, sae->prime, elem) < 0 ||
+           crypto_bignum_inverse(elem, sae->prime, elem) < 0 ||
+           crypto_bignum_to_bin(elem, sae->own_commit_element,
+                                sizeof(sae->own_commit_element),
+                                sae->prime_len) < 0) {
+               wpa_printf(MSG_DEBUG, "SAE: Could not compute commit-element");
+               goto fail;
+       }
+
+       wpa_hexdump(MSG_DEBUG, "SAE: commit-element",
+                   sae->own_commit_element, sae->prime_len);
+
+       ret = 0;
+fail:
+       crypto_bignum_deinit(elem, 0);
+       crypto_bignum_deinit(mask, 1);
+       crypto_bignum_deinit(bn_rand, 1);
+       crypto_bignum_deinit(x, 1);
+       return ret;
+}
+
+
+static int sae_prepare_commit_dh(const u8 *addr1, const u8 *addr2,
+                                const u8 *password, size_t password_len,
+                                struct sae_data *sae)
+{
+       struct crypto_bignum *pwe;
+       int ret = 0;
+
+       pwe = crypto_bignum_init();
+       if (pwe == NULL ||
+           sae_derive_pwe_dh(sae, addr1, addr2, password, password_len, pwe) <
+           0 ||
+           sae_derive_commit_dh(sae, pwe) < 0)
+               ret = -1;
+
+       crypto_bignum_deinit(pwe, 1);
+
+       return ret;
+}
+
+
+int sae_prepare_commit(const u8 *addr1, const u8 *addr2,
+                      const u8 *password, size_t password_len,
+                      struct sae_data *sae)
+{
+       if (sae->ec) {
+               return sae_prepare_commit_ec(addr1, addr2, password,
+                                            password_len, sae);
+       }
+
+       if (sae->dh) {
+               return sae_prepare_commit_dh(addr1, addr2, password,
+                                            password_len, sae);
+       }
+
+       return -1;
+}
+
+
 static int sae_check_peer_commit(struct sae_data *sae)
 {
        u8 order[SAE_MAX_PRIME_LEN], prime[SAE_MAX_PRIME_LEN];
@@ -341,6 +630,16 @@ static int sae_check_peer_commit(struct sae_data *sae)
                return -1;
        }
 
+       if (sae->dh) {
+               if (os_memcmp(sae->peer_commit_element, prime, sae->prime_len)
+                   >= 0 ||
+                   val_zero_or_one(sae->peer_commit_element, sae->prime_len)) {
+                       wpa_printf(MSG_DEBUG, "SAE: Invalid peer element");
+                       return -1;
+               }
+               return 0;
+       }
+
        /* element x and y coordinates < p */
        if (os_memcmp(sae->peer_commit_element, prime, sae->prime_len) >= 0 ||
            os_memcmp(sae->peer_commit_element + sae->prime_len, prime,
@@ -354,7 +653,7 @@ static int sae_check_peer_commit(struct sae_data *sae)
 }
 
 
-static int sae_derive_k(struct sae_data *sae, u8 *k)
+static int sae_derive_k_ec(struct sae_data *sae, u8 *k)
 {
        struct crypto_ec_point *pwe, *peer_elem, *K;
        struct crypto_bignum *rand_bn, *peer_scalar;
@@ -403,6 +702,58 @@ fail:
 }
 
 
+static int sae_derive_k_dh(struct sae_data *sae, u8 *k)
+{
+       struct crypto_bignum *pwe, *peer_elem, *K, *rand_bn, *peer_scalar;
+       int ret = -1;
+
+       pwe = crypto_bignum_init_set(sae->pwe, sae->prime_len);
+       peer_scalar = crypto_bignum_init_set(sae->peer_commit_scalar,
+                                            sae->prime_len);
+       peer_elem = crypto_bignum_init_set(sae->peer_commit_element,
+                                          sae->prime_len);
+       K = crypto_bignum_init();
+       rand_bn = crypto_bignum_init_set(sae->sae_rand, sae->prime_len);
+       if (pwe == NULL || peer_elem == NULL || peer_scalar == NULL ||
+           K == NULL || rand_bn == NULL)
+               goto fail;
+
+       /*
+        * K = scalar-op(rand, (elem-op(scalar-op(peer-commit-scalar, PWE),
+        *                                        PEER-COMMIT-ELEMENT)))
+        * If K is identity element (one), reject.
+        * k = F(K) (= x coordinate)
+        */
+
+       if (crypto_bignum_exptmod(pwe, peer_scalar, sae->prime, K) < 0 ||
+           crypto_bignum_mulmod(K, peer_elem, sae->prime, K) < 0 ||
+           crypto_bignum_exptmod(K, rand_bn, sae->prime, K) < 0 ||
+           crypto_bignum_to_bin(K, k, SAE_MAX_PRIME_LEN, sae->prime_len) < 0 ||
+           val_one(k, sae->prime_len)) {
+               wpa_printf(MSG_DEBUG, "SAE: Failed to calculate K and k");
+               goto fail;
+       }
+
+       wpa_hexdump_key(MSG_DEBUG, "SAE: k", k, sae->prime_len);
+
+       ret = 0;
+fail:
+       crypto_bignum_deinit(pwe, 1);
+       crypto_bignum_deinit(peer_elem, 0);
+       crypto_bignum_deinit(K, 1);
+       crypto_bignum_deinit(rand_bn, 1);
+       return ret;
+}
+
+
+static int sae_derive_k(struct sae_data *sae, u8 *k)
+{
+       if (sae->ec)
+               return sae_derive_k_ec(sae, k);
+       return sae_derive_k_dh(sae, k);
+}
+
+
 static int sae_derive_keys(struct sae_data *sae, const u8 *k)
 {
        u8 null_key[SAE_KEYSEED_KEY_LEN], val[SAE_MAX_PRIME_LEN];
@@ -467,7 +818,8 @@ void sae_write_commit(struct sae_data *sae, struct wpabuf *buf,
        if (token)
                wpabuf_put_buf(buf, token);
        wpabuf_put_data(buf, sae->own_commit_scalar, sae->prime_len);
-       wpabuf_put_data(buf, sae->own_commit_element, 2 * sae->prime_len);
+       wpabuf_put_data(buf, sae->own_commit_element,
+                       (sae->ec ? 2 : 1) * sae->prime_len);
 }
 
 
@@ -509,10 +861,15 @@ u16 sae_parse_commit(struct sae_data *sae, const u8 *data, size_t len,
                           group);
                return WLAN_STATUS_FINITE_CYCLIC_GROUP_NOT_SUPPORTED;
        }
+       if (sae->dh && !allowed_groups) {
+               wpa_printf(MSG_DEBUG, "SAE: Do not allow FFC group %u without "
+                          "explicit configuration enabling it", group);
+               return WLAN_STATUS_FINITE_CYCLIC_GROUP_NOT_SUPPORTED;
+       }
        pos += 2;
 
-       if (pos + 3 * sae->prime_len < end) {
-               size_t tlen = end - (pos + 3 * sae->prime_len);
+       if (pos + (sae->ec ? 3 : 2) * sae->prime_len < end) {
+               size_t tlen = end - (pos + (sae->ec ? 3 : 2) * sae->prime_len);
                wpa_hexdump(MSG_DEBUG, "SAE: Anti-Clogging Token", pos, tlen);
                if (token)
                        *token = pos;
@@ -544,6 +901,19 @@ u16 sae_parse_commit(struct sae_data *sae, const u8 *data, size_t len,
                    sae->peer_commit_scalar, sae->prime_len);
        pos += sae->prime_len;
 
+       if (sae->dh) {
+               if (pos + sae->prime_len > end) {
+                       wpa_printf(MSG_DEBUG, "SAE: Not enough data for "
+                                  "commit-element");
+                       return WLAN_STATUS_UNSPECIFIED_FAILURE;
+               }
+               os_memcpy(sae->peer_commit_element, pos, sae->prime_len);
+               wpa_hexdump(MSG_DEBUG, "SAE: Peer commit-element",
+                           sae->peer_commit_element, sae->prime_len);
+
+               return WLAN_STATUS_SUCCESS;
+       }
+
        if (pos + 2 * sae->prime_len > end) {
                wpa_printf(MSG_DEBUG, "SAE: Not enough data for "
                           "commit-element");
@@ -581,11 +951,11 @@ void sae_write_confirm(struct sae_data *sae, struct wpabuf *buf)
        addr[1] = sae->own_commit_scalar;
        len[1] = sae->prime_len;
        addr[2] = sae->own_commit_element;
-       len[2] = 2 * sae->prime_len;
+       len[2] = (sae->ec ? 2 : 1) * sae->prime_len;
        addr[3] = sae->peer_commit_scalar;
        len[3] = sae->prime_len;
        addr[4] = sae->peer_commit_element;
-       len[4] = 2 * sae->prime_len;
+       len[4] = (sae->ec ? 2 : 1) * sae->prime_len;
        hmac_sha256_vector(sae->kck, sizeof(sae->kck), 5, addr, len,
                           wpabuf_put(buf, SHA256_MAC_LEN));
 }
@@ -619,11 +989,11 @@ int sae_check_confirm(struct sae_data *sae, const u8 *data, size_t len)
        addr[1] = sae->peer_commit_scalar;
        elen[1] = sae->prime_len;
        addr[2] = sae->peer_commit_element;
-       elen[2] = 2 * sae->prime_len;
+       elen[2] = (sae->ec ? 2 : 1) * sae->prime_len;
        addr[3] = sae->own_commit_scalar;
        elen[3] = sae->prime_len;
        addr[4] = sae->own_commit_element;
-       elen[4] = 2 * sae->prime_len;
+       elen[4] = (sae->ec ? 2 : 1) * sae->prime_len;
        hmac_sha256_vector(sae->kck, sizeof(sae->kck), 5, addr, elen, verifier);
 
        if (os_memcmp(verifier, data + 2, SHA256_MAC_LEN) != 0) {

diff --git a/src/common/sae.h b/src/common/sae.h
index 46ca84d..bcd50a0 100644 (file)
--- a/src/common/sae.h
+++ b/src/common/sae.h
@@ -13,7 +13,7 @@
 #define SAE_PMK_LEN 32
 #define SAE_PMKID_LEN 16
 #define SAE_KEYSEED_KEY_LEN 32
-#define SAE_MAX_PRIME_LEN 66
+#define SAE_MAX_PRIME_LEN 512
 #define SAE_COMMIT_MAX_LEN (2 + 3 * SAE_MAX_PRIME_LEN)
 #define SAE_CONFIRM_MAX_LEN (2 + SAE_MAX_PRIME_LEN)
 
@@ -31,8 +31,12 @@ struct sae_data {
        int group;
        struct crypto_ec *ec;
        int prime_len;
+       const struct dh_group *dh;
        const struct crypto_bignum *prime;
        const struct crypto_bignum *order;
+       struct crypto_bignum *prime_buf;
+       struct crypto_bignum *order_buf;
+       int safe_prime;
 };
 
 int sae_set_group(struct sae_data *sae, int group);

diff --git a/wpa_supplicant/Android.mk b/wpa_supplicant/Android.mk
index 7dce6e6..1cf6444 100644 (file)
--- a/wpa_supplicant/Android.mk
+++ b/wpa_supplicant/Android.mk
@@ -183,6 +183,7 @@ ifdef CONFIG_SAE
 L_CFLAGS += -DCONFIG_SAE
 OBJS += src/common/sae.c
 NEED_ECC=y
+NEED_DH_GROUPS=y
 endif
 
 ifdef CONFIG_TDLS

diff --git a/wpa_supplicant/Makefile b/wpa_supplicant/Makefile
index 4348e52..672e62b 100644 (file)
--- a/wpa_supplicant/Makefile
+++ b/wpa_supplicant/Makefile
@@ -176,6 +176,7 @@ ifdef CONFIG_SAE
 CFLAGS += -DCONFIG_SAE
 OBJS += ../src/common/sae.o
 NEED_ECC=y
+NEED_DH_GROUPS=y
 endif
 
 ifdef CONFIG_WNM