laforge has uploaded this change for review. (
https://gerrit.osmocom.org/c/libosmocore/+/33092 )
Change subject: libosmogsm: Factor out the C2 derivation function
......................................................................
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
---
M include/osmocom/crypt/auth.h
M src/gsm/auth_core.c
M src/gsm/libosmogsm.map
M src/gsm/milenage/milenage.c
4 files changed, 47 insertions(+), 7 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/92/33092/1
diff --git a/include/osmocom/crypt/auth.h b/include/osmocom/crypt/auth.h
index 2f8804b..a42ad7a 100644
--- a/include/osmocom/crypt/auth.h
+++ b/include/osmocom/crypt/auth.h
@@ -142,5 +142,6 @@
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[]);
+void osmo_auth_c2(uint8_t sres[4], const uint8_t *res, size_t res_len, uint8_t
sres_deriv_func);
/* @} */
diff --git a/src/gsm/auth_core.c b/src/gsm/auth_core.c
index 1fa1d79..e99f71d 100644
--- a/src/gsm/auth_core.c
+++ b/src/gsm/auth_core.c
@@ -343,4 +343,32 @@
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 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);
+
+ 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);
+ }
+}
+
/*! @} */
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 8de3b54..dc7663e 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -561,6 +561,7 @@
osmo_auth_load;
osmo_auth_register;
osmo_auth_supported;
+osmo_auth_c2;
osmo_auth_c3;
osmo_sub_auth_type_names;
diff --git a/src/gsm/milenage/milenage.c b/src/gsm/milenage/milenage.c
index 3c14ab9..ba9ab33 100644
--- a/src/gsm/milenage/milenage.c
+++ b/src/gsm/milenage/milenage.c
@@ -244,19 +244,13 @@
int gsm_milenage(const u8 *opc, const u8 *k, const u8 *_rand, u8 *sres, u8 *kc)
{
u8 res[8], ck[16], ik[16];
- int i;
if (milenage_f2345(opc, k, _rand, res, ck, ik, NULL, NULL))
return -1;
osmo_auth_c3(kc, ck, ik);
+ osmo_auth_c2(sres, res, sizeof(res), 1);
-#ifdef GSM_MILENAGE_ALT_SRES
- os_memcpy(sres, res, 4);
-#else /* GSM_MILENAGE_ALT_SRES */
- for (i = 0; i < 4; i++)
- sres[i] = res[i] ^ res[i + 4];
-#endif /* GSM_MILENAGE_ALT_SRES */
return 0;
}
--
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Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: I0e7cd55f5578f891cb6cc1b0442920ba5beddae4
Gerrit-Change-Number: 33092
Gerrit-PatchSet: 1
Gerrit-Owner: laforge <[email protected]>
Gerrit-MessageType: newchange
