/*! \file auth_milenage.c
* GSM/GPRS/3G authentication core infrastructure */
/*
* (C) 2011 by Harald Welte <laforge@gnumonks.org>
*
* All Rights Reserved
*
* SPDX-License-Identifier: GPL-2.0+
*
* 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 <osmocom/crypt/auth.h>
#include <osmocom/core/bits.h>
#include "milenage/common.h"
#include "milenage/milenage.h"
/*! \addtogroup auth
* @{
*/
static const uint8_t *gen_opc_if_needed(const struct osmo_sub_auth_data *aud, uint8_t *gen_opc)
{
int rc;
/* Check if we only know OP and compute OPC if required */
if (aud->type == OSMO_AUTH_TYPE_UMTS && aud->u.umts.opc_is_op) {
rc = milenage_opc_gen(gen_opc, aud->u.umts.k, aud->u.umts.opc);
if (rc < 0)
return NULL;
return gen_opc;
} else
return aud->u.umts.opc;
}
static int milenage_gen_vec(struct osmo_auth_vector *vec,
struct osmo_sub_auth_data *aud,
const uint8_t *_rand)
{
size_t res_len = sizeof(vec->res);
uint64_t next_sqn;
uint8_t gen_opc[16];
const uint8_t *opc;
uint8_t sqn[6];
uint64_t ind_mask;
uint64_t seq_1;
int rc;
opc = gen_opc_if_needed(aud, gen_opc);
if (!opc)
return -1;
/* Determine next SQN, according to 3GPP TS 33.102:
* SQN consists of SEQ and a lower significant part of IND bits:
*
* |----------SEQ------------|
* |------------------------SQN-----------|
* |-----IND----|
*
* The IND part is used as "slots": e.g. a given HLR client will always
* get the same IND part, called ind here, with incrementing SEQ. In
* the USIM, each IND slot enforces that its SEQ are used in ascending
* order -- as long as that constraint is satisfied, the SQN may jump
* forwards and backwards. For example, for ind_bitlen == 5, asking the
* USIM for SQN = 32, 64, 33 is allowed, because 32 and 64 are
* SEQ || (ind == 0), and though 33 is below 64, it is ind == 1 and
* allowed. Not allowed would be 32, 96, 64, because 64 would go
* backwards after 96, both being ind == 0.
*
* From the last used SQN, we want to increment SEQ + 1, and then pick
* the matching IND part.
*
* IND size is suggested in TS 33.102 as 5 bits. SQN is 48 bits long.
* If ind_bitlen is passed too large here, the algorithms will break
* down. But at which point should we return an error? A sane limit
* seems to be ind_bitlen == 10, but to protect against failure,
* limiting ind_bitlen to 28 is enough, 28 being the number of bits
* suggested for the delta in 33.102, which is discussed to still
* require 2^15 > 32000 authentications to wrap the SQN back to the
* start.
*
* Note that if a caller with ind == 1 generates N vectors, the SQN
* stored after this will reflect SEQ + N. If then another caller with
* ind == 2 generates another N vectors, this will then use SEQ + N
* onwards and end up with SEQ + N + N. In other words, most of each
* SEQ's IND slots will remain unused. When looking at SQN being 48
* bits wide, after dropping ind_bitlen (say 5) from it, we will still
* have a sequence range of 2^43 = 8.8e12, eight trillion sequences,
* which is large enough to not bother further. With the maximum
* ind_bitlen of 28 enforced below, we still get more than 1 million
* sequences, which is also sufficiently large.
*
* An ind_bitlen of zero may be passed from legacy callers that are not
* aware of the IND extension. For these, below algorithm works out as
* before, simply incrementing SQN by 1.
*
* This is also a mechanism for tools like the osmo-auc-gen to directly
* request a given SQN to be used. With ind_bitlen == 0 the caller can
* be sure that this code will increment SQN by exactly one before
* generating a tuple, thus a caller would simply pass
* { .ind_bitlen = 0, .ind = 0, .sqn = (desired_sqn - 1) }
*/
if (aud->u.umts.ind_bitlen > OSMO_MILENAGE_IND_BITLEN_MAX)
return -2;
seq_1 = 1LL << aud->u.umts.ind_bitlen;
ind_mask = ~(seq_1 - 1);
/* the ind index must not affect the SEQ part */
if (aud->u.umts.ind >= seq_1)
return -3;
/* keep the incremented SQN local until gsm_milenage() succeeded. */
next_sqn = ((aud->u.umts.sqn + seq_1) & ind_mask) + aud->u.umts.ind;
osmo_store64be_ext(next_sqn, sqn, 6);
milenage_generate(opc, aud->u.umts.amf, aud->u.umts.k,
sqn, _rand,
vec->autn, vec->ik, vec->ck, vec->res, &res_len);
vec->res_len = res_len;
rc = gsm_milenage(opc, aud->u.umts.k, _rand, vec->sres, vec->kc);
if (rc < 0)
return rc;
vec->auth_types = OSMO_AUTH_TYPE_UMTS | OSMO_AUTH_TYPE_GSM;
/* for storage in the caller's AUC database */
aud->u.umts.sqn = next_sqn;
return 0;
}
static int milenage_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 sqn_out[6];
uint8_t gen_opc[16];
const uint8_t *opc;
int rc;
opc = gen_opc_if_needed(aud, gen_opc);
rc = milenage_auts(opc, aud->u.umts.k, rand_auts, auts, sqn_out);
if (rc < 0)
return rc;
aud->u.umts.sqn_ms = osmo_load64be_ext(sqn_out, 6) >> 16;
/* Update our "largest used SQN" from the USIM -- milenage_gen_vec()
* below will increment SQN. */
aud->u.umts.sqn = aud->u.umts.sqn_ms;
return milenage_gen_vec(vec, aud, _rand);
}
static struct osmo_auth_impl milenage_alg = {
.algo = OSMO_AUTH_ALG_MILENAGE,
.name = "MILENAGE (libosmogsm built-in)",
.priority = 1000,
.gen_vec = &milenage_gen_vec,
.gen_vec_auts = &milenage_gen_vec_auts,
};
static __attribute__((constructor)) void on_dso_load_milenage(void)
{
osmo_auth_register(&milenage_alg);
}
/*! @} */