iwd/src/eap-aka.c

/*
 *
 *  Wireless daemon for Linux
 *
 *  Copyright (C) 2017  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 <ctype.h>
#include <stdio.h>
#include <errno.h>
#include <ell/ell.h>

#include "crypto.h"
#include "simutil.h"

/*
 * EAP-AKA specific values
 */
#define EAP_AKA_KI_LEN		16
#define EAP_AKA_OPC_LEN		16
#define EAP_AKA_AMF_LEN		2
#define EAP_AKA_SQN_LEN		6
#define EAP_AKA_IK_LEN		16
#define EAP_AKA_CK_LEN		16
#define EAP_AKA_AUTN_LEN	16
#define EAP_AKA_RES_LEN		8
#define EAP_AKA_K_RE_LEN	32

#define EAP_AKA_ST_CHALLENGE	0x01
#define EAP_AKA_ST_AUTH_REJECT	0x02
#define EAP_AKA_ST_SYNC_FAILURE	0x04
#define EAP_AKA_ST_IDENTITY	0x05
#define EAP_AKA_ST_NOTIFICATION	0x0c
#define EAP_AKA_ST_CLIENT_ERROR	0x0e

/*
 * Internal client state, tracked to ensure that we are receiving the right
 * messages at the right time.
 */
enum eap_aka_state {
	EAP_AKA_STATE_UNCONNECTED = 0,
	EAP_AKA_STATE_IDENTITY,
	EAP_AKA_STATE_CHALLENGE,
	EAP_AKA_STATE_SUCCESS,
	EAP_AKA_STATE_ERROR
};

struct eap_aka_handle {
	enum eap_aka_state state;
	/* Identity from SIM */
	char *identity;

	/* Derived master key */
	uint8_t mk[EAP_SIM_MK_LEN];

	/* Derived K_encr key from PRNG */
	uint8_t k_encr[EAP_SIM_K_ENCR_LEN];

	/* Derived K_aut key from PRNG */
	uint8_t k_aut[EAP_SIM_K_AUT_LEN];

	/* Derived MSK from PRNG */
	uint8_t msk[EAP_SIM_MSK_LEN];

	/* Derived EMSK from PRNG */
	uint8_t emsk[EAP_SIM_EMSK_LEN];

	/* Flag set if AT_ANY_ID_REQ was present */
	bool any_id_req : 1;

	/* Flag to indicate protected status indications */
	bool protected : 1;

	/* Subscriber key */
	uint8_t ki[EAP_AKA_KI_LEN];

	/* Key derived from OP and ki */
	uint8_t opc[EAP_AKA_OPC_LEN];

	/* Authentication management field */
	uint8_t amf[EAP_AKA_AMF_LEN];

	/* Sequence number */
	uint8_t sqn[EAP_AKA_SQN_LEN];

	/* Integrity key */
	uint8_t ik[EAP_AKA_IK_LEN];

	/* Signed response */
	uint8_t res[EAP_AKA_RES_LEN];

	/* Confidentiality key */
	uint8_t ck[EAP_AKA_CK_LEN];

	/* Authentication value from AuC */
	uint8_t autn[EAP_AKA_AUTN_LEN];
};

static int eap_aka_probe(struct eap_state *eap, const char *name)
{
	struct eap_aka_handle *aka;

	if (strcasecmp(name, "AKA"))
		return -ENOTSUP;

	aka = l_new(struct eap_aka_handle, 1);

	eap_set_data(eap, aka);

	return 0;
}

static void eap_aka_remove(struct eap_state *eap)
{
	struct eap_aka_handle *aka = eap_get_data(eap);

	l_free(aka->identity);
	l_free(aka);

	eap_set_data(eap, NULL);
}

static bool derive_aka_mk(const char *identity, uint8_t *ik, uint8_t *ck,
		uint8_t *mk)
{
	int ret;
	struct iovec iov[5];
	struct l_checksum *checksum = l_checksum_new(L_CHECKSUM_SHA1);

	if (!checksum) {
		l_error("could not create SHA1 checksum");
		return false;
	}

	iov[0].iov_base = (void *)identity;
	iov[0].iov_len = strlen(identity);
	iov[1].iov_base = (void *)ik;
	iov[1].iov_len = EAP_AKA_IK_LEN;
	iov[2].iov_base = (void *)ck;
	iov[2].iov_len = EAP_AKA_CK_LEN;

	if (!l_checksum_updatev(checksum, iov, 3))
		goto mk_error;

	ret = l_checksum_get_digest(checksum, mk, EAP_SIM_MK_LEN);
	l_checksum_free(checksum);

	return (ret == EAP_SIM_MK_LEN);

mk_error:
	l_checksum_free(checksum);
	l_error("error deriving master key");
	return false;
}

/*
 * Handles EAP-AKA Challenge subtype
 */
static void handle_challenge(struct eap_state *eap, const uint8_t *pkt,
		size_t len)
{
	struct eap_aka_handle *aka = eap_get_data(eap);
	struct eap_sim_tlv_iter iter;
	uint8_t prng_buf[160];
	size_t resp_len = 40;
	uint8_t response[resp_len + 4];
	uint8_t *pos = response;
	const uint8_t *rand = NULL;
	const uint8_t *autn = NULL;

	if (len < 3) {
		l_error("packet is too small");
		goto chal_error;
	}

	if (aka->state != EAP_AKA_STATE_IDENTITY) {
		l_error("invalid packet for EAP-AKA state");
		goto chal_error;
	}

	eap_sim_tlv_iter_init(&iter, pkt + 3, len - 3);

	while (eap_sim_tlv_iter_next(&iter)) {
		const uint8_t *contents = eap_sim_tlv_iter_get_data(&iter);
		uint16_t length = eap_sim_tlv_iter_get_length(&iter);

		switch (eap_sim_tlv_iter_get_type(&iter)) {
		case EAP_SIM_AT_AUTN:
			if (length < EAP_AKA_AUTN_LEN + 2) {
				l_error("malformed AT_AUTN");
				goto chal_error;
			}

			autn = contents + 2;

			break;

		case EAP_SIM_AT_RAND:
			if (length < EAP_SIM_RAND_LEN + 2) {
				l_error("malformed AT_RAND");
				goto chal_error;
			}

			rand = contents + 2;

			break;

		case EAP_SIM_AT_RESULT_IND:
			if (length < 2) {
				l_error("malformed AT_RESULT_IND");
				goto chal_error;
			}

			aka->protected = 1;
			resp_len += 4;

			break;

		case EAP_SIM_AT_NEXT_PSEUDONYM:
		case EAP_SIM_AT_NEXT_REAUTH_ID:
		case EAP_SIM_AT_IV:
		case EAP_SIM_AT_ENCR_DATA:
		case EAP_SIM_AT_PADDING:
		case EAP_SIM_AT_CHECKCODE:
		case EAP_SIM_AT_MAC:
		/*
		 * AT_BIDDING is defined in RFC 5448 (AKA'). It is used to
		 * communicate support for AKA', if supported.
		 */
		case EAP_SIM_AT_BIDDING:
			/* RFC 4187, Section 10.1 */
			break;

		default:
			l_error("attribute %u was found in Challenge",
					eap_sim_tlv_iter_get_type(&iter));
			goto chal_error;
		}
	}

	eap_aka_get_milenage(aka->opc, aka->ki, rand, aka->sqn, aka->amf,
			aka->autn, aka->ck, aka->ik, aka->res);

	if (memcmp(autn, aka->autn, EAP_AKA_AUTN_LEN)) {
		l_error("EAP_SIM_AT_AUTN is not valid");
		goto chal_error;
	}

	if (!derive_aka_mk(aka->identity, aka->ik, aka->ck, aka->mk)) {
		l_error("error deriving MK");
		goto chal_fatal;
	}

	eap_sim_fips_prf(aka->mk, 20, prng_buf, 160);

	if (!eap_sim_get_encryption_keys(prng_buf, aka->k_encr, aka->k_aut,
			aka->msk, aka->emsk)) {
		l_error("could not derive encryption keys");
		goto chal_fatal;
	}

	if (!eap_sim_verify_mac(eap, EAP_TYPE_AKA, pkt, len, aka->k_aut, NULL,
			0)) {
		l_error("MAC was not valid");
		goto chal_error;
	}

	aka->state = EAP_AKA_STATE_CHALLENGE;

	pos += eap_sim_build_header(eap, EAP_TYPE_AKA, EAP_AKA_ST_CHALLENGE,
			pos, resp_len);
	pos += eap_sim_add_attribute(pos, EAP_SIM_AT_RES,
			EAP_SIM_PAD_LENGTH_BITS, aka->res, EAP_AKA_RES_LEN);

	if (aka->protected)
		pos += eap_sim_add_attribute(pos, EAP_SIM_AT_RESULT_IND,
				EAP_SIM_PAD_NONE, NULL, 2);

	pos += eap_sim_add_attribute(pos, EAP_SIM_AT_MAC, EAP_SIM_PAD_NONE,
			NULL, EAP_SIM_MAC_LEN);

	if (!eap_sim_derive_mac(response, resp_len, aka->k_aut,
			pos - EAP_SIM_MAC_LEN)) {
		l_error("error deriving MAC");
		goto chal_fatal;
	}

	eap_send_response(eap, EAP_TYPE_AKA, response, resp_len);

	if (!aka->protected) {
		eap_method_success(eap);
		eap_set_key_material(eap, aka->msk, 32, NULL, 0, NULL, 0);

		aka->state = EAP_AKA_STATE_SUCCESS;
	}

	return;

chal_fatal:
	eap_method_error(eap);
	aka->state = EAP_AKA_STATE_ERROR;
	return;

chal_error:
	eap_sim_client_error(eap, EAP_TYPE_AKA, EAP_SIM_ERROR_PROCESS);
}

/*
 * Handles Notification subtype
 */
static void handle_notification(struct eap_state *eap, const uint8_t *pkt,
		size_t len)
{
	struct eap_aka_handle *aka = eap_get_data(eap);
	struct eap_sim_tlv_iter iter;
	int32_t value = -1;

	if (len < 3) {
		l_error("packet is too small");
		goto notif_error;
	}

	eap_sim_tlv_iter_init(&iter, pkt + 3, len - 3);

	while (eap_sim_tlv_iter_next(&iter)) {
		const uint8_t *contents = eap_sim_tlv_iter_get_data(&iter);
		uint16_t length = eap_sim_tlv_iter_get_length(&iter);

		switch (eap_sim_tlv_iter_get_type(&iter)) {
		case EAP_SIM_AT_NOTIFICATION:
			if (length < 2) {
				l_error("malformed AT_NOTIFICATION");
				goto notif_error;
			}

			value = l_get_be16(contents);
			break;

		case EAP_SIM_AT_IV:
		case EAP_SIM_AT_ENCR_DATA:
		case EAP_SIM_AT_PADDING:
		case EAP_SIM_AT_MAC:
			/* RFC 4186, Section 10.1 */
			break;

		default:
			l_error("attribute type %u not allowed in Notification",
					eap_sim_tlv_iter_get_type(&iter));
			goto notif_error;
		}
	}

	if (value == EAP_SIM_SUCCESS && aka->protected &&
			aka->state == EAP_AKA_STATE_CHALLENGE) {
		/* header + MAC + MAC header */
		uint8_t response[8 + EAP_SIM_MAC_LEN + 4];
		uint8_t *pos = response;

		/*
		 * Server sent successful result indication
		 */
		eap_method_success(eap);
		eap_set_key_material(eap, aka->msk, 32, NULL, 0, NULL, 0);

		/*
		 * Build response packet
		 */
		pos += eap_sim_build_header(eap, EAP_TYPE_AKA,
				EAP_AKA_ST_NOTIFICATION, pos, 20);
		pos += eap_sim_add_attribute(pos, EAP_SIM_AT_MAC,
				EAP_SIM_PAD_NONE, NULL, EAP_SIM_MAC_LEN);

		if (!eap_sim_derive_mac(response, pos - response, aka->k_aut,
				response + 12)) {
			l_error("could not derive MAC");
			eap_method_error(eap);
			aka->state = EAP_AKA_STATE_ERROR;
			return;
		}

		eap_send_response(eap, EAP_TYPE_AKA, response, pos - response);

		aka->state = EAP_AKA_STATE_SUCCESS;

		return;
	} else if (value == EAP_SIM_SUCCESS) {
		/*
		 * Unexpected success notification, what should
		 * be done here?
		 */
		l_error("Unexpected success notification");
	} else {
		/*
		 * All other values are error conditions.
		 * Nothing unique can be done for any error so
		 * print the code and signal EAP failure.
		 */
		l_error("Error authenticating: code=%u", value);
	}

notif_error:
	eap_sim_client_error(eap, EAP_TYPE_AKA, EAP_SIM_ERROR_PROCESS);
}

static void handle_identity(struct eap_state *eap, const uint8_t *pkt,
		size_t len)
{
	struct eap_aka_handle *aka = eap_get_data(eap);
	uint8_t response[8 + strlen(aka->identity) + 4];
	uint8_t *pos = response;

	if (aka->state != EAP_AKA_STATE_UNCONNECTED) {
		l_error("invalid packet for EAP-AKA state");
		eap_sim_client_error(eap, EAP_TYPE_AKA, EAP_SIM_ERROR_PROCESS);
		return;
	}

	aka->state = EAP_AKA_STATE_IDENTITY;
	/*
	 * Build response packet
	 */
	pos += eap_sim_build_header(eap, EAP_TYPE_AKA, EAP_AKA_ST_IDENTITY, pos,
			20);
	pos += eap_sim_add_attribute(pos, EAP_SIM_AT_IDENTITY,
			EAP_SIM_PAD_LENGTH, (uint8_t *)aka->identity,
			strlen(aka->identity));

	eap_send_response(eap, EAP_TYPE_AKA, response, pos - response);
}

static void eap_aka_handle_request(struct eap_state *eap,
					const uint8_t *pkt, size_t len)
{
	if (len < 1) {
		l_error("packet is too small");
		goto req_error;
	}

	switch (pkt[0]) {
	case EAP_AKA_ST_IDENTITY:
		handle_identity(eap, pkt, len);
		break;

	case EAP_AKA_ST_CHALLENGE:
		handle_challenge(eap, pkt, len);
		break;

	case EAP_AKA_ST_NOTIFICATION:
		handle_notification(eap, pkt, len);
		break;

	default:
		l_error("unknown EAP-SIM subtype: %u", pkt[0]);
		goto req_error;
	}

	return;

req_error:
	eap_sim_client_error(eap, EAP_TYPE_AKA, EAP_SIM_ERROR_PROCESS);
}

static bool eap_aka_load_settings(struct eap_state *eap,
					struct l_settings *settings,
					const char *prefix)
{
	struct eap_aka_handle *aka = eap_get_data(eap);
	char setting[64];
	const char *imsi;
	const char *ki;
	const char *opc;
	const char *amf;
	const char *sqn;
	size_t len;

	snprintf(setting, sizeof(setting), "%sAKA-IMSI", prefix);
	imsi = l_settings_get_value(settings, "Security", setting);
	if (imsi)
		aka->identity = l_strdup(imsi);

	snprintf(setting, sizeof(setting), "%sAKA-KI", prefix);
	ki = l_settings_get_value(settings, "Security", setting);
	if (ki) {
		uint8_t *val = l_util_from_hexstring(ki, &len);

		memcpy(aka->ki, val, len);
		l_free(val);
	}

	snprintf(setting, sizeof(setting), "%sAKA-OPC", prefix);
	opc = l_settings_get_value(settings, "Security", setting);
	if (opc) {
		uint8_t *val = l_util_from_hexstring(opc, &len);

		memcpy(aka->opc, val, len);
		l_free(val);
	}

	snprintf(setting, sizeof(setting), "%sAKA-AMF", prefix);
	amf = l_settings_get_value(settings, "Security", setting);
	if (amf) {
		uint8_t *val = l_util_from_hexstring(amf, &len);

		memcpy(aka->amf, val, len);
		l_free(val);
	}

	snprintf(setting, sizeof(setting), "%sAKA-SQN", prefix);
	sqn = l_settings_get_value(settings, "Security", setting);
	if (sqn) {
		uint8_t *val = l_util_from_hexstring(sqn, &len);

		memcpy(aka->sqn, val, len);
		l_free(val);
	}

	return true;
}

static struct eap_method eap_aka = {
	.request_type = EAP_TYPE_AKA,
	.exports_msk = true,
	.name = "AKA",
	.probe = eap_aka_probe,
	.remove = eap_aka_remove,
	.handle_request = eap_aka_handle_request,
	.load_settings = eap_aka_load_settings,
};

static int eap_aka_init(void)
{
	l_debug("");
	return eap_register_method(&eap_aka);
}

static void eap_aka_exit(void)
{
	l_debug("");
	eap_unregister_method(&eap_aka);
}

EAP_METHOD_BUILTIN(eap_aka, eap_aka_init, eap_aka_exit)