Sylvain Munaut | f1d3344 | 2011-04-23 15:34:11 +0200 | [diff] [blame] | 1 | /* |
| 2 | * a5.c |
| 3 | * |
| 4 | * Full reimplementation of A5/1,2 (split and threadsafe) |
| 5 | * |
| 6 | * The logic behind the algorithm is taken from "A pedagogical implementation |
| 7 | * of the GSM A5/1 and A5/2 "voice privacy" encryption algorithms." by |
| 8 | * Marc Briceno, Ian Goldberg, and David Wagner. |
| 9 | * |
| 10 | * Copyright (C) 2011 Sylvain Munaut <tnt@246tNt.com> |
| 11 | * |
| 12 | * All Rights Reserved |
| 13 | * |
| 14 | * This program is free software; you can redistribute it and/or modify |
| 15 | * it under the terms of the GNU General Public License as published by |
| 16 | * the Free Software Foundation; either version 2 of the License, or |
| 17 | * (at your option) any later version. |
| 18 | * |
| 19 | * This program is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 22 | * GNU General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU General Public License along |
| 25 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 26 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
| 27 | */ |
| 28 | |
| 29 | #include <string.h> |
| 30 | |
| 31 | #include <osmocom/gsm/a5.h> |
| 32 | |
| 33 | void |
| 34 | osmo_a5(int n, uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) |
| 35 | { |
| 36 | switch (n) |
| 37 | { |
| 38 | case 0: |
| 39 | if (dl) |
| 40 | memset(dl, 0x00, 114); |
| 41 | if (ul) |
| 42 | memset(ul, 0x00, 114); |
| 43 | break; |
| 44 | |
| 45 | case 1: |
| 46 | osmo_a5_1(key, fn, dl, ul); |
| 47 | break; |
| 48 | |
| 49 | case 2: |
| 50 | osmo_a5_2(key, fn, dl, ul); |
| 51 | break; |
| 52 | |
| 53 | default: |
| 54 | /* a5/[3..7] not supported here/yet */ |
| 55 | break; |
| 56 | } |
| 57 | } |
| 58 | |
| 59 | |
| 60 | /* ------------------------------------------------------------------------ */ |
| 61 | /* A5/1&2 common stuff */ |
| 62 | /* ------------------------------------------------------------------------ */ |
| 63 | |
| 64 | #define A5_R1_LEN 19 |
| 65 | #define A5_R2_LEN 22 |
| 66 | #define A5_R3_LEN 23 |
| 67 | #define A5_R4_LEN 17 /* A5/2 only */ |
| 68 | |
| 69 | #define A5_R1_MASK ((1<<A5_R1_LEN)-1) |
| 70 | #define A5_R2_MASK ((1<<A5_R2_LEN)-1) |
| 71 | #define A5_R3_MASK ((1<<A5_R3_LEN)-1) |
| 72 | #define A5_R4_MASK ((1<<A5_R4_LEN)-1) |
| 73 | |
| 74 | #define A5_R1_TAPS 0x072000 /* x^19 + x^5 + x^2 + x + 1 */ |
| 75 | #define A5_R2_TAPS 0x300000 /* x^22 + x + 1 */ |
| 76 | #define A5_R3_TAPS 0x700080 /* x^23 + x^15 + x^2 + x + 1 */ |
| 77 | #define A5_R4_TAPS 0x010800 /* x^17 + x^5 + 1 */ |
| 78 | |
| 79 | static inline uint32_t |
| 80 | _a5_12_parity(uint32_t x) |
| 81 | { |
| 82 | x ^= x >> 16; |
| 83 | x ^= x >> 8; |
| 84 | x ^= x >> 4; |
| 85 | x ^= x >> 2; |
| 86 | x ^= x >> 1; |
| 87 | return x & 1; |
| 88 | } |
| 89 | |
| 90 | static inline uint32_t |
| 91 | _a5_12_majority(uint32_t v1, uint32_t v2, uint32_t v3) |
| 92 | { |
| 93 | return (!!v1 + !!v2 + !!v3) >= 2; |
| 94 | } |
| 95 | |
| 96 | static inline uint32_t |
| 97 | _a5_12_clock(uint32_t r, uint32_t mask, uint32_t taps) |
| 98 | { |
| 99 | return ((r << 1) & mask) | _a5_12_parity(r & taps); |
| 100 | } |
| 101 | |
| 102 | |
| 103 | /* ------------------------------------------------------------------------ */ |
| 104 | /* A5/1 */ |
| 105 | /* ------------------------------------------------------------------------ */ |
| 106 | |
| 107 | #define A51_R1_CLKBIT 0x000100 |
| 108 | #define A51_R2_CLKBIT 0x000400 |
| 109 | #define A51_R3_CLKBIT 0x000400 |
| 110 | |
| 111 | static inline void |
| 112 | _a5_1_clock(uint32_t r[], int force) |
| 113 | { |
| 114 | int cb[3], maj; |
| 115 | |
| 116 | cb[0] = !!(r[0] & A51_R1_CLKBIT); |
| 117 | cb[1] = !!(r[1] & A51_R2_CLKBIT); |
| 118 | cb[2] = !!(r[2] & A51_R3_CLKBIT); |
| 119 | |
| 120 | maj = _a5_12_majority(cb[0], cb[1], cb[2]); |
| 121 | |
| 122 | if (force || (maj == cb[0])) |
| 123 | r[0] = _a5_12_clock(r[0], A5_R1_MASK, A5_R1_TAPS); |
| 124 | |
| 125 | if (force || (maj == cb[1])) |
| 126 | r[1] = _a5_12_clock(r[1], A5_R2_MASK, A5_R2_TAPS); |
| 127 | |
| 128 | if (force || (maj == cb[2])) |
| 129 | r[2] = _a5_12_clock(r[2], A5_R3_MASK, A5_R3_TAPS); |
| 130 | } |
| 131 | |
| 132 | static inline uint8_t |
| 133 | _a5_1_get_output(uint32_t r[]) |
| 134 | { |
| 135 | return (r[0] >> (A5_R1_LEN-1)) ^ |
| 136 | (r[1] >> (A5_R2_LEN-1)) ^ |
| 137 | (r[2] >> (A5_R3_LEN-1)); |
| 138 | } |
| 139 | |
| 140 | void |
| 141 | osmo_a5_1(uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) |
| 142 | { |
| 143 | uint32_t r[3] = {0, 0, 0}; |
| 144 | uint32_t fn_count; |
| 145 | uint32_t b; |
| 146 | int i; |
| 147 | |
| 148 | /* Key load */ |
| 149 | for (i=0; i<64; i++) |
| 150 | { |
| 151 | b = ( key[7 - (i>>3)] >> (i&7) ) & 1; |
| 152 | |
| 153 | _a5_1_clock(r, 1); |
| 154 | |
| 155 | r[0] ^= b; |
| 156 | r[1] ^= b; |
| 157 | r[2] ^= b; |
| 158 | } |
| 159 | |
| 160 | /* Frame count load */ |
| 161 | fn_count = osmo_a5_fn_count(fn); |
| 162 | |
| 163 | for (i=0; i<22; i++) |
| 164 | { |
| 165 | b = (fn_count >> i) & 1; |
| 166 | |
| 167 | _a5_1_clock(r, 1); |
| 168 | |
| 169 | r[0] ^= b; |
| 170 | r[1] ^= b; |
| 171 | r[2] ^= b; |
| 172 | } |
| 173 | |
| 174 | /* Mix */ |
| 175 | for (i=0; i<100; i++) |
| 176 | { |
| 177 | _a5_1_clock(r, 0); |
| 178 | } |
| 179 | |
| 180 | /* Output */ |
| 181 | for (i=0; i<114; i++) { |
| 182 | _a5_1_clock(r, 0); |
| 183 | if (dl) |
| 184 | dl[i] = _a5_1_get_output(r); |
| 185 | } |
| 186 | |
| 187 | for (i=0; i<114; i++) { |
| 188 | _a5_1_clock(r, 0); |
| 189 | if (ul) |
| 190 | ul[i] = _a5_1_get_output(r); |
| 191 | } |
| 192 | } |
| 193 | |
| 194 | |
| 195 | /* ------------------------------------------------------------------------ */ |
| 196 | /* A5/2 */ |
| 197 | /* ------------------------------------------------------------------------ */ |
| 198 | |
| 199 | #define A52_R4_CLKBIT0 0x000400 |
| 200 | #define A52_R4_CLKBIT1 0x000008 |
| 201 | #define A52_R4_CLKBIT2 0x000080 |
| 202 | |
| 203 | static inline void |
| 204 | _a5_2_clock(uint32_t r[], int force) |
| 205 | { |
| 206 | int cb[3], maj; |
| 207 | |
| 208 | cb[0] = !!(r[3] & A52_R4_CLKBIT0); |
| 209 | cb[1] = !!(r[3] & A52_R4_CLKBIT1); |
| 210 | cb[2] = !!(r[3] & A52_R4_CLKBIT2); |
| 211 | |
| 212 | maj = (cb[0] + cb[1] + cb[2]) >= 2; |
| 213 | |
| 214 | if (force || (maj == cb[0])) |
| 215 | r[0] = _a5_12_clock(r[0], A5_R1_MASK, A5_R1_TAPS); |
| 216 | |
| 217 | if (force || (maj == cb[1])) |
| 218 | r[1] = _a5_12_clock(r[1], A5_R2_MASK, A5_R2_TAPS); |
| 219 | |
| 220 | if (force || (maj == cb[2])) |
| 221 | r[2] = _a5_12_clock(r[2], A5_R3_MASK, A5_R3_TAPS); |
| 222 | |
| 223 | r[3] = _a5_12_clock(r[3], A5_R4_MASK, A5_R4_TAPS); |
| 224 | } |
| 225 | |
| 226 | static inline uint8_t |
| 227 | _a5_2_get_output(uint32_t r[], uint8_t *db) |
| 228 | { |
| 229 | uint8_t cb, tb; |
| 230 | |
| 231 | tb = (r[0] >> (A5_R1_LEN-1)) ^ |
| 232 | (r[1] >> (A5_R2_LEN-1)) ^ |
| 233 | (r[2] >> (A5_R3_LEN-1)); |
| 234 | |
| 235 | cb = *db; |
| 236 | |
| 237 | *db = ( tb ^ |
| 238 | _a5_12_majority( r[0] & 0x08000, ~r[0] & 0x04000, r[0] & 0x1000) ^ |
| 239 | _a5_12_majority(~r[1] & 0x10000, r[1] & 0x02000, r[1] & 0x0200) ^ |
| 240 | _a5_12_majority( r[2] & 0x40000, r[2] & 0x10000, ~r[2] & 0x2000) |
| 241 | ); |
| 242 | |
| 243 | return cb; |
| 244 | } |
| 245 | |
| 246 | void |
| 247 | osmo_a5_2(uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul) |
| 248 | { |
| 249 | uint32_t r[4] = {0, 0, 0, 0}; |
| 250 | uint32_t fn_count; |
| 251 | uint32_t b; |
| 252 | uint8_t db = 0, o; |
| 253 | int i; |
| 254 | |
| 255 | /* Key load */ |
| 256 | for (i=0; i<64; i++) |
| 257 | { |
| 258 | b = ( key[7 - (i>>3)] >> (i&7) ) & 1; |
| 259 | |
| 260 | _a5_2_clock(r, 1); |
| 261 | |
| 262 | r[0] ^= b; |
| 263 | r[1] ^= b; |
| 264 | r[2] ^= b; |
| 265 | r[3] ^= b; |
| 266 | } |
| 267 | |
| 268 | /* Frame count load */ |
| 269 | fn_count = osmo_a5_fn_count(fn); |
| 270 | |
| 271 | for (i=0; i<22; i++) |
| 272 | { |
| 273 | b = (fn_count >> i) & 1; |
| 274 | |
| 275 | _a5_2_clock(r, 1); |
| 276 | |
| 277 | r[0] ^= b; |
| 278 | r[1] ^= b; |
| 279 | r[2] ^= b; |
| 280 | r[3] ^= b; |
| 281 | } |
| 282 | |
| 283 | r[0] |= 1 << 15; |
| 284 | r[1] |= 1 << 16; |
| 285 | r[2] |= 1 << 18; |
| 286 | r[3] |= 1 << 10; |
| 287 | |
| 288 | /* Mix */ |
| 289 | for (i=0; i<100; i++) |
| 290 | { |
| 291 | _a5_2_clock(r, 0); |
| 292 | } |
| 293 | |
| 294 | _a5_2_get_output(r, &db); |
| 295 | |
| 296 | |
| 297 | /* Output */ |
| 298 | for (i=0; i<114; i++) { |
| 299 | _a5_2_clock(r, 0); |
| 300 | o = _a5_2_get_output(r, &db); |
| 301 | if (dl) |
| 302 | dl[i] = o; |
| 303 | } |
| 304 | |
| 305 | for (i=0; i<114; i++) { |
| 306 | _a5_2_clock(r, 0); |
| 307 | o = _a5_2_get_output(r, &db); |
| 308 | if (ul) |
| 309 | ul[i] = o; |
| 310 | } |
| 311 | } |