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libosmocore/src/gsm/auth_core.c

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/* (C) 2010-2023 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.
*
*/
#include "config.h"
#include <errno.h>
#include <stdint.h>
#include <string.h>
#include <osmocom/core/utils.h>
#include <osmocom/core/linuxlist.h>
#include <osmocom/core/plugin.h>
#include <osmocom/crypt/auth.h>
/*! \addtogroup auth
* @{
* GSM/GPRS/3G authentication core infrastructure
*
* \file auth_core.c */
static LLIST_HEAD(osmo_auths);
/* generate auth_data2 from auth_data (for legacy API/ABI compatibility */
static int auth_data2auth_data2(struct osmo_sub_auth_data2 *out, const struct osmo_sub_auth_data *in)
{
out->type = in->type;
out->algo = in->algo;
switch (in->type) {
case OSMO_AUTH_TYPE_NONE:
return 0;
case OSMO_AUTH_TYPE_GSM:
memcpy(out->u.gsm.ki, in->u.gsm.ki, sizeof(out->u.gsm.ki));
break;
case OSMO_AUTH_TYPE_UMTS:
memcpy(out->u.umts.opc, in->u.umts.opc, sizeof(in->u.umts.opc));
out->u.umts.opc_len = sizeof(in->u.umts.opc);
memcpy(out->u.umts.k, in->u.umts.k, sizeof(in->u.umts.k));
out->u.umts.k_len = sizeof(in->u.umts.k);
memcpy(out->u.umts.amf, in->u.umts.amf, sizeof(out->u.umts.amf));
out->u.umts.sqn = in->u.umts.sqn;
out->u.umts.opc_is_op = in->u.umts.opc_is_op;
out->u.umts.ind_bitlen = in->u.umts.ind_bitlen;
out->u.umts.ind = in->u.umts.ind;
out->u.umts.sqn_ms = in->u.umts.sqn_ms;
break;
default:
return -EINVAL;
}
return 0;
}
static struct osmo_auth_impl *selected_auths[_OSMO_AUTH_ALG_NUM];
/*! Register an authentication algorithm implementation with the core
* \param[in] impl Structure describing implementation and it's callbacks
* \returns 0 on success, or a negative error code on failure
*
* This function is called by an authentication implementation plugin to
* register itself with the authentication core.
*/
int osmo_auth_register(struct osmo_auth_impl *impl)
{
if (impl->algo >= ARRAY_SIZE(selected_auths))
return -ERANGE;
llist_add_tail(&impl->list, &osmo_auths);
/* check if we want to select this implementation over others */
if (!selected_auths[impl->algo] ||
(selected_auths[impl->algo]->priority > impl->priority))
selected_auths[impl->algo] = impl;
return 0;
}
/*! Load all available authentication plugins from the given path
* \param[in] path Path name of the directory containing the plugins
* \returns number of plugins loaded in case of success, negative in case of error
*
* This function will load all plugins contained in the specified path.
*/
int osmo_auth_load(const char *path)
{
/* load all plugins available from path */
#if !defined(EMBEDDED)
return osmo_plugin_load_all(path);
#else
return -1;
#endif
}
/*! Determine if a given authentication algorithm is supported
* \param[in] algo Algorithm which should be checked
* \returns 1 if algo is supported, 0 if not, negative error on failure
*
* This function is used by an application to determine at runtime if a
* given authentication algorithm is supported or not.
*/
int osmo_auth_supported(enum osmo_auth_algo algo)
{
if (algo >= ARRAY_SIZE(selected_auths))
return -ERANGE;
if (selected_auths[algo])
return 1;
return 0;
}
/* 3GPP TS 33.102 §6.8.2.3 C5 function to derive UMTS IK from GSM Kc */
static inline void c5_function(uint8_t *ik, const uint8_t *kc)
{
unsigned int i;
for (i = 0; i < 4; i++)
ik[i] = kc[i] ^ kc[i+4];
memcpy(ik+4, kc, 8);
for (i = 12; i < 16; i++)
ik[i] = ik[i-12];
}
/* 3GPP TS 33.102 §6.8.2.3 C4 function to derive UMTS CK from GSM Kc */
void osmo_c4(uint8_t *ck, const uint8_t *kc)
{
memcpy(ck, kc, 8);
memcpy(ck+8, kc, 8);
}
/*! Generate 3G CK + IK from 2G authentication vector
* \param vec Authentication Vector to be modified
* \returns 1 if the vector was changed, 0 otherwise
*
* This function performs the C5 and C4 functions to derive the UMTS key
* material from the GSM key material in the supplied vector, _if_ the input
* vector doesn't yet have UMTS authentication capability.
*/
int osmo_auth_3g_from_2g(struct osmo_auth_vector *vec)
{
if ((vec->auth_types & OSMO_AUTH_TYPE_GSM) &&
!(vec->auth_types & OSMO_AUTH_TYPE_UMTS)) {
c5_function(vec->ik, vec->kc);
osmo_c4(vec->ck, vec->kc);
/* We cannot actually set OSMO_AUTH_TYPE_UMTS as we have no
* AUTN and no RES, and thus can only perform GSM
* authentication with this tuple.
*/
return 1;
}
return 0;
}
/*! Generate authentication vector
* \param[out] vec Generated authentication vector. See below!
* \param[in] aud Subscriber-specific key material
* \param[in] _rand Random challenge to be used
* \returns 0 on success, negative error on failure
*
* This function performs the core cryptographic function of the AUC,
* computing authentication triples/quintuples based on the permanent
* subscriber data and a random value. The result is what is forwarded
* by the AUC via HLR and VLR to the MSC which will then be able to
* invoke authentication with the MS.
*
* Contrary to the older osmo_auth_gen_vec(), the caller must specify
* the desired RES length in the vec->res_len field prior to calling
* this function. The requested length must match the capabilities of
* the chosen algorithm (e.g. 4/8 for MILENAGE).
*/
int osmo_auth_gen_vec2(struct osmo_auth_vector *vec,
struct osmo_sub_auth_data2 *aud,
const uint8_t *_rand)
{
struct osmo_auth_impl *impl = selected_auths[aud->algo];
int rc;
if (!impl)
return -ENOENT;
rc = impl->gen_vec(vec, aud, _rand);
if (rc < 0)
return rc;
memcpy(vec->rand, _rand, sizeof(vec->rand));
return 0;
}
/*! Generate authentication vector
* \param[out] vec Generated authentication vector
* \param[in] aud Subscriber-specific key material
* \param[in] _rand Random challenge to be used
* \returns 0 on success, negative error on failure
*
* This function performs the core cryptographic function of the AUC,
* computing authentication triples/quintuples based on the permanent
* subscriber data and a random value. The result is what is forwarded
* by the AUC via HLR and VLR to the MSC which will then be able to
* invoke authentication with the MS
*/
int osmo_auth_gen_vec(struct osmo_auth_vector *vec,
struct osmo_sub_auth_data *aud,
const uint8_t *_rand)
{
struct osmo_sub_auth_data2 aud2;
int rc;
if (aud->type == OSMO_AUTH_TYPE_UMTS) {
/* old API callers are not expected to initialize this struct field,
* and always expect an 8-byte RES value */
vec->res_len = 8;
}
rc = auth_data2auth_data2(&aud2, aud);
if (rc < 0)
return rc;
rc = osmo_auth_gen_vec2(vec, &aud2, _rand);
if (aud->type == OSMO_AUTH_TYPE_UMTS)
aud->u.umts.sqn = aud2.u.umts.sqn;
return rc;
}
/*! Generate authentication vector and re-sync sequence
* \param[out] vec Generated authentication vector. See below!
* \param[in] aud Subscriber-specific key material
* \param[in] auts AUTS value sent by the SIM/MS
* \param[in] rand_auts RAND value sent by the SIM/MS
* \param[in] _rand Random challenge to be used to generate vector
* \returns 0 on success, negative error on failure
*
* This function performs a special variant of the core cryptographic
* function of the AUC: computing authentication triples/quintuples
* based on the permanent subscriber data, a random value as well as the
* AUTS and RAND values returned by the SIM/MS. This special variant is
* needed if the sequence numbers between MS and AUC have for some
* reason become different.
*
* Contrary to the older osmo_auth_gen_vec_auts(), the caller must specify
* the desired RES length in the vec->res_len field prior to calling
* this function. The requested length must match the capabilities of
* the chosen algorithm (e.g. 4/8 for MILENAGE).
*/
int osmo_auth_gen_vec_auts2(struct osmo_auth_vector *vec,
struct osmo_sub_auth_data2 *aud,
const uint8_t *auts, const uint8_t *rand_auts,
const uint8_t *_rand)
{
struct osmo_auth_impl *impl = selected_auths[aud->algo];
int rc;
if (!impl || !impl->gen_vec_auts)
return -ENOENT;
rc = impl->gen_vec_auts(vec, aud, auts, rand_auts, _rand);
if (rc < 0)
return rc;
memcpy(vec->rand, _rand, sizeof(vec->rand));
return 0;
}
/*! Generate authentication vector and re-sync sequence
* \param[out] vec Generated authentication vector
* \param[in] aud Subscriber-specific key material
* \param[in] auts AUTS value sent by the SIM/MS
* \param[in] rand_auts RAND value sent by the SIM/MS
* \param[in] _rand Random challenge to be used to generate vector
* \returns 0 on success, negative error on failure
*
* This function performs a special variant of the core cryptographic
* function of the AUC: computing authentication triples/quintuples
* based on the permanent subscriber data, a random value as well as the
* AUTS and RAND values returned by the SIM/MS. This special variant is
* needed if the sequence numbers between MS and AUC have for some
* reason become different.
*/
int osmo_auth_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)
{
struct osmo_sub_auth_data2 aud2;
int rc;
if (aud->type == OSMO_AUTH_TYPE_UMTS) {
/* old API callers are not expected to initialize this struct field,
* and always expect an 8-byte RES value */
vec->res_len = 8;
}
rc = auth_data2auth_data2(&aud2, aud);
if (rc < 0)
return rc;
rc = osmo_auth_gen_vec_auts2(vec, &aud2, auts, rand_auts, _rand);
if (aud->type == OSMO_AUTH_TYPE_UMTS) {
aud->u.umts.sqn = aud2.u.umts.sqn;
aud->u.umts.sqn_ms = aud2.u.umts.sqn_ms;
}
return rc;
}
static const struct value_string auth_alg_vals[] = {
{ OSMO_AUTH_ALG_NONE, "None" },
{ OSMO_AUTH_ALG_COMP128v1, "COMP128v1" },
{ OSMO_AUTH_ALG_COMP128v2, "COMP128v2" },
{ OSMO_AUTH_ALG_COMP128v3, "COMP128v3" },
{ OSMO_AUTH_ALG_XOR_3G, "XOR-3G" },
{ OSMO_AUTH_ALG_MILENAGE, "MILENAGE" },
{ OSMO_AUTH_ALG_XOR_2G, "XOR-2G" },
{ OSMO_AUTH_ALG_TUAK, "TUAK" },
{ 0, NULL }
};
/*! Get human-readable name of authentication algorithm */
const char *osmo_auth_alg_name(enum osmo_auth_algo alg)
{
return get_value_string(auth_alg_vals, alg);
}
/*! Parse human-readable name of authentication algorithm */
enum osmo_auth_algo osmo_auth_alg_parse(const char *name)
{
return get_string_value(auth_alg_vals, name);
}
const struct value_string osmo_sub_auth_type_names[] = {
{ OSMO_AUTH_TYPE_NONE, "None" },
{ OSMO_AUTH_TYPE_GSM, "GSM" },
{ OSMO_AUTH_TYPE_UMTS, "UMTS" },
{ 0, NULL }
};
/* Derive GSM AKA ciphering key Kc from UMTS AKA CK and IK (auth function c3 from 3GPP TS 33.103 §
* 4.6.1).
* \param[out] kc GSM AKA Kc, 8 byte target buffer.
* \param[in] ck UMTS AKA CK, 16 byte input buffer.
* \param[in] ik UMTS AKA IK, 16 byte input buffer.
*/
void osmo_auth_c3(uint8_t kc[], const uint8_t ck[], const uint8_t ik[])
{
int i;
for (i = 0; i < 8; i++)
kc[i] = ck[i] ^ ck[i + 8] ^ ik[i] ^ ik[i + 8];
}
/*! Derive GSM SRES from UMTS [X]RES (auth function c2 from 3GPP TS 33.103 Section 6.8.1.2
* \param[out] sres GSM SRES value, 4 byte target buffer
* \param[in] res UMTS XRES, 4..16 bytes input buffer
* \param[in] res_len length of res parameter (in bytes)
* \param[in] sres_deriv_func SRES derivation function (1 or 2, see 3GPP TS 55.205 Section 4
*/
void osmo_auth_c2(uint8_t sres[4], const uint8_t *res, size_t res_len, uint8_t sres_deriv_func)
{
uint8_t xres[16];
OSMO_ASSERT(sres_deriv_func == 1 || sres_deriv_func == 2);
OSMO_ASSERT(res_len <= sizeof(xres));
memcpy(xres, res, res_len);
/* zero-pad the end, if XRES is < 16 bytes */
if (res_len < sizeof(xres))
memset(xres+res_len, 0, sizeof(xres)-res_len);
if (sres_deriv_func == 1) {
/* SRES derivation function #1 */
for (unsigned int i = 0; i < 4; i++)
sres[i] = xres[i] ^ xres[4+i] ^ xres[8+i] ^ xres[12+i];
} else {
/* SRES derivation function #2 */
memcpy(sres, xres, 4);
}
}
/*! @} */
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