diff options
Diffstat (limited to 'src/gsm')
| -rw-r--r-- | src/gsm/a5.c | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/src/gsm/a5.c b/src/gsm/a5.c index 31c2ba95..36978c48 100644 --- a/src/gsm/a5.c +++ b/src/gsm/a5.c @@ -26,10 +26,28 @@ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. */ +/*! \addtogroup a5 + * @{ + */ + +/*! \file gsm/a5.c + * \brief Osmocom GSM A5 ciphering algorithm implementation + */ + #include <string.h> #include <osmocom/gsm/a5.h> +/*! \brief Main method to generate a A5/x cipher stream + * \param[in] n Which A5/x method to use + * \param[in] key 8 byte array for the key (as received from the SIM) + * \param[in] fn Frame number + * \param[out] dl Pointer to array of ubits to return Downlink cipher stream + * \param[out] ul Pointer to array of ubits to return Uplink cipher stream + * + * Currently A5/[0-2] are supported. + * Either (or both) of dl/ul can be NULL if not needed. + */ void osmo_a5(int n, const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) { @@ -76,6 +94,10 @@ osmo_a5(int n, const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) #define A5_R3_TAPS 0x700080 /* x^23 + x^15 + x^2 + x + 1 */ #define A5_R4_TAPS 0x010800 /* x^17 + x^5 + 1 */ +/*! \brief Computes parity of a 32-bit word + * \param[in] x 32 bit word + * \return Parity bit (xor of all bits) as 0 or 1 + */ static inline uint32_t _a5_12_parity(uint32_t x) { @@ -87,12 +109,24 @@ _a5_12_parity(uint32_t x) return x & 1; } +/*! \brief Compute majority bit from 3 taps + * \param[in] v1 LFSR state ANDed with tap-bit + * \param[in] v2 LFSR state ANDed with tap-bit + * \param[in] v3 LFSR state ANDed with tap-bit + * \return The majority bit (0 or 1) + */ static inline uint32_t _a5_12_majority(uint32_t v1, uint32_t v2, uint32_t v3) { return (!!v1 + !!v2 + !!v3) >= 2; } +/*! \brief Compute the next LFSR state + * \param[in] r Current state + * \param[in] mask LFSR mask + * \param[in] taps LFSR taps + * \return Next state + */ static inline uint32_t _a5_12_clock(uint32_t r, uint32_t mask, uint32_t taps) { @@ -108,6 +142,10 @@ _a5_12_clock(uint32_t r, uint32_t mask, uint32_t taps) #define A51_R2_CLKBIT 0x000400 #define A51_R3_CLKBIT 0x000400 +/*! \brief GSM A5/1 Clocking function + * \param[in] r Register state + * \param[in] force Non-zero value disable conditional clocking + */ static inline void _a5_1_clock(uint32_t r[], int force) { @@ -129,6 +167,10 @@ _a5_1_clock(uint32_t r[], int force) r[2] = _a5_12_clock(r[2], A5_R3_MASK, A5_R3_TAPS); } +/*! \brief GSM A5/1 Output function + * \param[in] r Register state + * \return The A5/1 output function bit + */ static inline uint8_t _a5_1_get_output(uint32_t r[]) { @@ -137,6 +179,14 @@ _a5_1_get_output(uint32_t r[]) (r[2] >> (A5_R3_LEN-1)); } +/*! \brief Generate a GSM A5/1 cipher stream + * \param[in] key 8 byte array for the key (as received from the SIM) + * \param[in] fn Frame number + * \param[out] dl Pointer to array of ubits to return Downlink cipher stream + * \param[out] ul Pointer to array of ubits to return Uplink cipher stream + * + * Either (or both) of dl/ul can be NULL if not needed. + */ void osmo_a5_1(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) { @@ -200,6 +250,10 @@ osmo_a5_1(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) #define A52_R4_CLKBIT1 0x000008 #define A52_R4_CLKBIT2 0x000080 +/*! \brief GSM A5/2 Clocking function + * \param[in] r Register state + * \param[in] force Non-zero value disable conditional clocking + */ static inline void _a5_2_clock(uint32_t r[], int force) { @@ -223,6 +277,10 @@ _a5_2_clock(uint32_t r[], int force) r[3] = _a5_12_clock(r[3], A5_R4_MASK, A5_R4_TAPS); } +/*! \brief GSM A5/2 Output function + * \param[in] r Register state + * \return The A5/2 output function bit + */ static inline uint8_t _a5_2_get_output(uint32_t r[]) { @@ -238,6 +296,14 @@ _a5_2_get_output(uint32_t r[]) return b; } +/*! \brief Generate a GSM A5/1 cipher stream + * \param[in] key 8 byte array for the key (as received from the SIM) + * \param[in] fn Frame number + * \param[out] dl Pointer to array of ubits to return Downlink cipher stream + * \param[out] ul Pointer to array of ubits to return Uplink cipher stream + * + * Either (or both) of dl/ul can be NULL if not needed. + */ void osmo_a5_2(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) { @@ -298,3 +364,5 @@ osmo_a5_2(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) ul[i] = _a5_2_get_output(r); } } + +/*! }@ */ |