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/*! \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);
}
/*! @} */
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