libosmogsm: add support for XOR authentication

Change-Id: I1afaf0a9e2dce43aec87964bacefb21ed4d3d565
Related: OS#2475

2 files changed, 188 insertions, 1 deletions

diff --git a/src/gsm/Makefile.am b/src/gsm/Makefile.am
index 0aa0de37..f13ba9d3 100644
--- a/src/gsm/Makefile.am
+++ b/src/gsm/Makefile.am
@@ -26,7 +26,7 @@ libgsmint_la_SOURCES =  a5.c rxlev_stat.c tlv_parser.c comp128.c comp128v23.c \
 			gprs_cipher_core.c gprs_rlc.c gsm0480.c abis_nm.c gsm0502.c \
 			gsm0411_utils.c gsm0411_smc.c gsm0411_smr.c gsm0414.c \
 			lapd_core.c lapdm.c kasumi.c gsm29205.c gsm_04_08_gprs.c \
-			auth_core.c auth_comp128v1.c auth_comp128v23.c \
+			auth_core.c auth_comp128v1.c auth_comp128v23.c auth_xor.c \
 			auth_milenage.c milenage/aes-encblock.c gea.c \
 			milenage/aes-internal.c milenage/aes-internal-enc.c \
 			milenage/milenage.c gan.c ipa.c gsm0341.c apn.c \
diff --git a/src/gsm/auth_xor.c b/src/gsm/auth_xor.c
new file mode 100644
index 00000000..36e006e6
--- /dev/null
+++ b/src/gsm/auth_xor.c
@@ -0,0 +1,187 @@
+/*! \file auth_xor.c
+ * GSM/GPRS/3G authentication core infrastructure */
+/*
+ * (C) 2018 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2017 by sysmocom s.f.m.c. GmbH
+ *
+ * All Rights Reserved
+ *
+ * Author: Daniel Willmann <dwillmann@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+
+#include <osmocom/core/bit64gen.h>
+#include <osmocom/crypt/auth.h>
+
+/*! \addtogroup auth
+ *  @{
+ */
+
+static void xor(uint8_t *out, const uint8_t *a, const uint8_t *b, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++)
+		out[i] = a[i] ^ b[i];
+}
+
+/* 3GPP TS 34.108, section 8.1.2.1 */
+static int xor_gen_vec(struct osmo_auth_vector *vec,
+		       struct osmo_sub_auth_data *aud,
+		       const uint8_t *_rand)
+{
+	uint8_t xdout[16], cdout[8];
+	uint8_t ak[6], xmac[8];
+	int i;
+
+	/* Step 1: xdout = (ki or k) ^ rand */
+	if (aud->type == OSMO_AUTH_TYPE_GSM)
+		xor(xdout, aud->u.gsm.ki, _rand, sizeof(xdout));
+	else if (aud->type == OSMO_AUTH_TYPE_UMTS)
+		xor(xdout, aud->u.umts.k, _rand, sizeof(xdout));
+	else
+		return -ENOTSUP;
+
+	/**
+	 * Step 2: res = xdout
+	 *
+	 * Suggested length for res is 128 bits, i.e. 16 bytes,
+	 * but also can be in range: 30 < n < 128 bits.
+	 */
+	memcpy(vec->res, xdout, sizeof(xdout));
+	vec->res_len = sizeof(xdout);
+
+	/* ck = xdout[1-15,0] */
+	memcpy(vec->ck, xdout + 1, sizeof(xdout) - 1);
+	vec->ck[15] = xdout[0];
+
+	/* ik = xdout[2-15,0-1] */
+	memcpy(vec->ik, xdout + 2, sizeof(xdout) - 2);
+	memcpy(vec->ik + sizeof(xdout) - 2, xdout, 2);
+
+	/* ak = xdout[3-8] */
+	memcpy(ak, xdout + 3, sizeof(ak));
+
+	/**
+	 * 3GPP TS 33.102, clause 6.8.1.2, b
+	 * sres = c2(res) = res[0-3] ^ res[4-7] ^ res[8-11] ^ res[12-15]
+	 */
+	for (i = 0; i < 4; i++) {
+		vec->sres[i]  = vec->res[i] ^ vec->res[i + 4];
+		vec->sres[i] ^= vec->res[i + 8] ^ vec->res[i + 12];
+	}
+
+	/**
+	 * 3GPP TS 33.102, clause 6.8.1.2, c
+	 * kc = c3(ck, ik) = ck[0-7] ^ ck[8-15] ^ ik[0-7] ^ ik[8-15]
+	 * FIXME: do we really have CK/IK for GSM?
+	 */
+	osmo_auth_c3(vec->kc, vec->ck, vec->ik);
+
+	/* The further part is UMTS specific */
+	if (aud->type != OSMO_AUTH_TYPE_UMTS) {
+		vec->auth_types = OSMO_AUTH_TYPE_GSM;
+		return 0;
+	}
+
+	/**
+	 * Step 3: cdout = sqn[0-5] || amf[0-1]
+	 * NOTE (for USIM): sqn[0-5] = autn[0-5] ^ ak[0-5]
+	 */
+	osmo_store64be_ext(aud->u.umts.sqn, cdout, 6);
+	memcpy(cdout + 6, aud->u.umts.amf, 2);
+
+	/* Step 4: xmac = xdout[0-8] ^ cdout[0-8] */
+	xor(xmac, xdout, cdout, sizeof(xmac));
+
+	/**
+	 * Step 5: autn = sqn ^ ak || amf || mac
+	 * NOTE: cdout still contains SQN from step 3
+	 */
+	xor(vec->autn, cdout, ak, sizeof(ak));
+	memcpy(vec->autn + 6, aud->u.umts.amf, 2);
+	memcpy(vec->autn + 8, xmac, sizeof(xmac));
+
+	vec->auth_types = OSMO_AUTH_TYPE_UMTS | OSMO_AUTH_TYPE_GSM;
+
+	return 0;
+}
+
+/* 3GPP TS 34.108, section 8.1.2.2 */
+static int xor_gen_vec_auts(struct osmo_auth_vector *vec,
+			    struct osmo_sub_auth_data *aud,
+			    const uint8_t *auts,
+			    const uint8_t *rand_auts,
+			    const uint8_t *_rand)
+{
+	uint8_t xdout[16], cdout[8];
+	uint8_t ak[6], xmac[8];
+	uint8_t sqnms[6];
+
+	/* Step 1: xdout = (ki or k) ^ rand */
+	if (aud->type == OSMO_AUTH_TYPE_GSM)
+		xor(xdout, aud->u.gsm.ki, _rand, sizeof(xdout));
+	else if (aud->type == OSMO_AUTH_TYPE_UMTS)
+		xor(xdout, aud->u.umts.k, _rand, sizeof(xdout));
+	else
+		return -ENOTSUP;
+
+	/* Step 2: ak = xdout[2-8] */
+	memcpy(ak, xdout + 3, 6);
+
+	/* sqnms = auts[0-5] ^ ak[0-5] */
+	xor(sqnms, auts, ak, sizeof(ak));
+
+	/* cdout = sqnms || amf* (dummy) */
+	memcpy(cdout, sqnms, 6);
+	memset(cdout + 6, 0x00, 2);
+
+	/* xmac = xdout[0-7] ^ cdout[0-7] */
+	xor(xmac, xdout, cdout, 8);
+
+	/* Compare the last 64 bits of received AUTS with the locally-generated MAC-S */
+	if (memcmp(auts + 6, xmac, 8))
+		return -1;
+
+	/* Update the "largest used SQN" from the USIM,
+	 * milenage_gen_vec() will increment it. */
+	aud->u.umts.sqn_ms = osmo_load64be_ext(sqnms, 6) >> 16;
+	aud->u.umts.sqn = aud->u.umts.sqn_ms;
+
+	return xor_gen_vec(vec, aud, _rand);
+}
+
+static struct osmo_auth_impl xor_alg = {
+	.algo = OSMO_AUTH_ALG_XOR,
+	.name = "XOR (libosmogsm built-in)",
+	.priority = 1000,
+	.gen_vec = &xor_gen_vec,
+	.gen_vec_auts = &xor_gen_vec_auts,
+};
+
+static __attribute__((constructor)) void on_dso_load_xor(void)
+{
+	osmo_auth_register(&xor_alg);
+}
+
+/*! @} */