EAP-pwd: Remove unused checks for cofactor > 1 cases

None of the ECC groups supported in the implementation had a cofactor
greater than 1, so these checks are unreachable and for all cases, the
cofactor is known to be 1. Furthermore, RFC 5931 explicitly disallow use
of ECC groups with cofactor larger than 1, so this checks cannot be
needed for any curve that is compliant with the RFC.

Remove the unneeded group cofactor checks to simplify the
implementation.

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

diff --git a/src/eap_common/eap_pwd_common.c b/src/eap_common/eap_pwd_common.c
index 00f85a390181a23d13d88a52df15da64cf9e033a..884150e6c1eb5620af27060946bbe6ef17014d39 100644 (file)
--- a/src/eap_common/eap_pwd_common.c
+++ b/src/eap_common/eap_pwd_common.c
@@ -151,7 +151,7 @@ int compute_password_element(EAP_PWD_group *grp, u16 num,
        u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_*
                       * mask */
        size_t primebytelen = 0, primebitlen;
-       struct crypto_bignum *x_candidate = NULL, *cofactor = NULL;
+       struct crypto_bignum *x_candidate = NULL;
        const struct crypto_bignum *prime;
        u8 mask, found_ctr = 0, is_odd = 0;
 
@@ -161,21 +161,15 @@ int compute_password_element(EAP_PWD_group *grp, u16 num,
        os_memset(x_bin, 0, sizeof(x_bin));
 
        prime = crypto_ec_get_prime(grp->group);
-       cofactor = crypto_bignum_init();
        grp->pwe = crypto_ec_point_init(grp->group);
        tmp1 = crypto_bignum_init();
        pm1 = crypto_bignum_init();
        one = crypto_bignum_init_set((const u8 *) "\x01", 1);
-       if (!cofactor || !grp->pwe || !tmp1 || !pm1 || !one) {
+       if (!grp->pwe || !tmp1 || !pm1 || !one) {
                wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums");
                goto fail;
        }
 
-       if (crypto_ec_cofactor(grp->group, cofactor) < 0) {
-               wpa_printf(MSG_INFO, "EAP-pwd: unable to get cofactor for "
-                          "curve");
-               goto fail;
-       }
        primebitlen = crypto_ec_prime_len_bits(grp->group);
        primebytelen = crypto_ec_prime_len(grp->group);
        if ((prfbuf = os_malloc(primebytelen)) == NULL) {
@@ -340,19 +334,6 @@ int compute_password_element(EAP_PWD_group *grp, u16 num,
                goto fail;
        }
 
-       if (!crypto_bignum_is_one(cofactor)) {
-               /* make sure the point is not in a small sub-group */
-               if (crypto_ec_point_mul(grp->group, grp->pwe, cofactor,
-                                       grp->pwe) != 0) {
-                       wpa_printf(MSG_INFO,
-                                  "EAP-pwd: cannot multiply generator by order");
-                       goto fail;
-               }
-               if (crypto_ec_point_is_at_infinity(grp->group, grp->pwe)) {
-                       wpa_printf(MSG_INFO, "EAP-pwd: point is at infinity");
-                       goto fail;
-               }
-       }
        wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %02d tries", found_ctr);
 
        if (0) {
@@ -362,7 +343,6 @@ int compute_password_element(EAP_PWD_group *grp, u16 num,
                ret = 1;
        }
        /* cleanliness and order.... */
-       crypto_bignum_deinit(cofactor, 1);
        crypto_bignum_deinit(x_candidate, 1);
        crypto_bignum_deinit(pm1, 0);
        crypto_bignum_deinit(tmp1, 1);
@@ -464,7 +444,6 @@ struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
        struct crypto_ec_point *element;
        const struct crypto_bignum *prime;
        size_t prime_len;
-       struct crypto_bignum *cofactor = NULL;
 
        prime = crypto_ec_get_prime(group->group);
        prime_len = crypto_ec_prime_len(group->group);
@@ -489,35 +468,7 @@ struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
                goto fail;
        }
 
-       cofactor = crypto_bignum_init();
-       if (!cofactor || crypto_ec_cofactor(group->group, cofactor) < 0) {
-               wpa_printf(MSG_INFO,
-                          "EAP-pwd: Unable to get cofactor for curve");
-               goto fail;
-       }
-
-       if (!crypto_bignum_is_one(cofactor)) {
-               struct crypto_ec_point *point;
-               int ok = 1;
-
-               /* check to ensure peer's element is not in a small sub-group */
-               point = crypto_ec_point_init(group->group);
-               if (!point ||
-                   crypto_ec_point_mul(group->group, element,
-                                       cofactor, point) != 0 ||
-                   crypto_ec_point_is_at_infinity(group->group, point))
-                       ok = 0;
-               crypto_ec_point_deinit(point, 0);
-
-               if (!ok) {
-                       wpa_printf(MSG_INFO,
-                                  "EAP-pwd: Small sub-group check on peer element failed");
-                       goto fail;
-               }
-       }
-
 out:
-       crypto_bignum_deinit(cofactor, 0);
        return element;
 fail:
        crypto_ec_point_deinit(element, 0);

diff --git a/src/eap_peer/eap_pwd.c b/src/eap_peer/eap_pwd.c
index 4be4fcf35f653579435fc5c12136ed250f638410..46894a52fec7d970e7ca7384f4b88f7b9404ccd3 100644 (file)
--- a/src/eap_peer/eap_pwd.c
+++ b/src/eap_peer/eap_pwd.c
@@ -309,7 +309,7 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
                                const u8 *payload, size_t payload_len)
 {
        struct crypto_ec_point *K = NULL;
-       struct crypto_bignum *mask = NULL, *cofactor = NULL;
+       struct crypto_bignum *mask = NULL;
        const u8 *ptr = payload;
        u8 *scalar, *element;
        size_t prime_len, order_len;
@@ -527,21 +527,14 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
 
        data->private_value = crypto_bignum_init();
        data->my_element = crypto_ec_point_init(data->grp->group);
-       cofactor = crypto_bignum_init();
        data->my_scalar = crypto_bignum_init();
        mask = crypto_bignum_init();
-       if (!data->private_value || !data->my_element || !cofactor ||
+       if (!data->private_value || !data->my_element ||
            !data->my_scalar || !mask) {
                wpa_printf(MSG_INFO, "EAP-PWD (peer): scalar allocation fail");
                goto fin;
        }
 
-       if (crypto_ec_cofactor(data->grp->group, cofactor) < 0) {
-               wpa_printf(MSG_INFO, "EAP-pwd (peer): unable to get cofactor "
-                          "for curve");
-               goto fin;
-       }
-
        if (eap_pwd_get_rand_mask(data->grp, data->private_value, mask,
                                  data->my_scalar) < 0)
                goto fin;
@@ -595,17 +588,8 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
                goto fin;
        }
 
-       /* ensure that the shared key isn't in a small sub-group */
-       if (!crypto_bignum_is_one(cofactor)) {
-               if (crypto_ec_point_mul(data->grp->group, K, cofactor, K) < 0) {
-                       wpa_printf(MSG_INFO, "EAP-PWD (peer): cannot multiply "
-                                  "shared key point by order");
-                       goto fin;
-               }
-       }
-
        /*
-        * This check is strictly speaking just for the case above where
+        * This check is strictly speaking just for the case where
         * co-factor > 1 but it was suggested that even though this is probably
         * never going to happen it is a simple and safe check "just to be
         * sure" so let's be safe.
@@ -644,7 +628,6 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
 
 fin:
        crypto_bignum_deinit(mask, 1);
-       crypto_bignum_deinit(cofactor, 1);
        crypto_ec_point_deinit(K, 1);
        if (data->outbuf == NULL)
                eap_pwd_state(data, FAILURE);

diff --git a/src/eap_server/eap_server_pwd.c b/src/eap_server/eap_server_pwd.c
index 9799c81971bfdf38c6257a568d319ef1a0f37cee..81ecd773fbf8243d73dc305734edeee60a6910bf 100644 (file)
--- a/src/eap_server/eap_server_pwd.c
+++ b/src/eap_server/eap_server_pwd.c
@@ -648,7 +648,6 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
                            const u8 *payload, size_t payload_len)
 {
        const u8 *ptr;
-       struct crypto_bignum *cofactor = NULL;
        struct crypto_ec_point *K = NULL;
        int res = 0;
        size_t prime_len, order_len;
@@ -667,20 +666,13 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
        }
 
        data->k = crypto_bignum_init();
-       cofactor = crypto_bignum_init();
        K = crypto_ec_point_init(data->grp->group);
-       if (!data->k || !cofactor || !K) {
+       if (!data->k || !K) {
                wpa_printf(MSG_INFO, "EAP-PWD (server): peer data allocation "
                           "fail");
                goto fin;
        }
 
-       if (crypto_ec_cofactor(data->grp->group, cofactor) < 0) {
-               wpa_printf(MSG_INFO, "EAP-PWD (server): unable to get "
-                          "cofactor for curve");
-               goto fin;
-       }
-
        /* element, x then y, followed by scalar */
        ptr = payload;
        data->peer_element = eap_pwd_get_element(data->grp, ptr);
@@ -718,18 +710,8 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
                goto fin;
        }
 
-       /* ensure that the shared key isn't in a small sub-group */
-       if (!crypto_bignum_is_one(cofactor)) {
-               if (crypto_ec_point_mul(data->grp->group, K, cofactor,
-                                       K) != 0) {
-                       wpa_printf(MSG_INFO, "EAP-PWD (server): cannot "
-                                  "multiply shared key point by order!\n");
-                       goto fin;
-               }
-       }
-
        /*
-        * This check is strictly speaking just for the case above where
+        * This check is strictly speaking just for the case where
         * co-factor > 1 but it was suggested that even though this is probably
         * never going to happen it is a simple and safe check "just to be
         * sure" so let's be safe.
@@ -748,7 +730,6 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
 
 fin:
        crypto_ec_point_deinit(K, 1);
-       crypto_bignum_deinit(cofactor, 1);
 
        if (res)
                eap_pwd_state(data, PWD_Confirm_Req);