diff options
| author | Harald Welte <laforge@osmocom.org> | 2023-05-30 15:57:08 +0200 |
|---|---|---|
| committer | laforge <laforge@osmocom.org> | 2023-06-02 08:29:55 +0000 |
| commit | 76f4c5cf5ca769b2913521965410599387c8acd9 (patch) | |
| tree | fa6dfc4b22f65d92647f66a0865546ff3b3ed408 /src/gsm/auth_core.c | |
| parent | d8e530952719fafe8aa512df085f3f568fde5cf2 (diff) | |
libosmogsm: Factor out the C2 derivation function
3GPP specifies the C2 derivation function (generating GSM SRES from UMTS XRES)
independent of the MILENAGE algorithm. So instead of open-coding it in
milenage.c:gsm_milenage(), let's create a separate public function
osmo_auth_c2() similar to the already-existing osmo_auth_c3() function.
gsm_milenage() can then simply use that function.
Change-Id: I0e7cd55f5578f891cb6cc1b0442920ba5beddae4
Diffstat (limited to 'src/gsm/auth_core.c')
| -rw-r--r-- | src/gsm/auth_core.c | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/src/gsm/auth_core.c b/src/gsm/auth_core.c index 2b6f35a7..ad5967d4 100644 --- a/src/gsm/auth_core.c +++ b/src/gsm/auth_core.c @@ -363,4 +363,33 @@ void osmo_auth_c3(uint8_t kc[], const uint8_t ck[], const uint8_t ik[]) 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); + } +} + /*! @} */ |