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add osmo_auth_c3() (separate from gsm_milenage()) 

To send a Ciphering Mode Command, we may need to derive a Kc from UMTS AKA
tokens. gsm_milenage() derives Kc from 3G tokens, but also derives an SRES.
For SRES, it requires an OPC, which may need to be derived from OP first. All
we need is a Kc, so we could feed a zero OPC ...  but to simplify the function
call for cases where just a Kc is required, separate the c3 function out from
gsm_milenage(), as osmo_auth_c3(). Obviously call osmo_auth_c3() from
gsm_milenage() (meaning that osmo-hlr's 55.205 derived auc tests still cover
exactly that implementation).

Prepares: If04e405426c55a81341747a9b450a69188525d5c (osmo-msc)
Related: OS#2745
Change-Id: I85a1d6ae95ad9e5ce9524ef7fc06414848afc2aa
This commit is contained in:
Neels Hofmeyr 2017-12-18 03:12:01 +01:00 committed by Harald Welte
parent d589f1dcfd
commit aa84b71f0f
4 changed files with 18 additions and 3 deletions
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2
include/osmocom/crypt/auth.h
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@ -105,4 +105,6 @@ void osmo_c4(uint8_t *ck, const uint8_t *kc);
const char *osmo_auth_alg_name(enum osmo_auth_algo alg);
enum osmo_auth_algo osmo_auth_alg_parse(const char *name);
void osmo_auth_c3(uint8_t kc[], const uint8_t ck[], const uint8_t ik[]);
/* @} */

13
src/gsm/auth_core.c
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@ -236,4 +236,17 @@ const struct value_string osmo_sub_auth_type_names[] = {
{ 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];
}
/*! @} */

1
src/gsm/libosmogsm.map
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@ -340,6 +340,7 @@ osmo_auth_3g_from_2g;
osmo_auth_load;
osmo_auth_register;
osmo_auth_supported;
osmo_auth_c3;
osmo_sub_auth_type_names;
osmo_rsl2sitype;

5
src/gsm/milenage/milenage.c
View File

@ -29,7 +29,7 @@
#include "common.h"
#include "aes_wrap.h"
#include "milenage.h"
#include <osmocom/crypt/auth.h>
/**
* milenage_f1 - Milenage f1 and f1* algorithms
@ -249,8 +249,7 @@ int gsm_milenage(const u8 *opc, const u8 *k, const u8 *_rand, u8 *sres, u8 *kc)
if (milenage_f2345(opc, k, _rand, res, ck, ik, NULL, NULL))
return -1;
for (i = 0; i < 8; i++)
kc[i] = ck[i] ^ ck[i + 8] ^ ik[i] ^ ik[i + 8];
osmo_auth_c3(kc, ck, ik);
#ifdef GSM_MILENAGE_ALT_SRES
os_memcpy(sres, res, 4);