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Linux/crypto/ansi_cprng.c

  1 /*
  2  * PRNG: Pseudo Random Number Generator
  3  *       Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
  4  *       AES 128 cipher
  5  *
  6  *  (C) Neil Horman <nhorman@tuxdriver.com>
  7  *
  8  *  This program is free software; you can redistribute it and/or modify it
  9  *  under the terms of the GNU General Public License as published by the
 10  *  Free Software Foundation; either version 2 of the License, or (at your
 11  *  any later version.
 12  *
 13  *
 14  */
 15 
 16 #include <crypto/internal/rng.h>
 17 #include <linux/err.h>
 18 #include <linux/init.h>
 19 #include <linux/module.h>
 20 #include <linux/moduleparam.h>
 21 #include <linux/string.h>
 22 
 23 #define DEFAULT_PRNG_KEY "0123456789abcdef"
 24 #define DEFAULT_PRNG_KSZ 16
 25 #define DEFAULT_BLK_SZ 16
 26 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
 27 
 28 /*
 29  * Flags for the prng_context flags field
 30  */
 31 
 32 #define PRNG_FIXED_SIZE 0x1
 33 #define PRNG_NEED_RESET 0x2
 34 
 35 /*
 36  * Note: DT is our counter value
 37  *       I is our intermediate value
 38  *       V is our seed vector
 39  * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
 40  * for implementation details
 41  */
 42 
 43 
 44 struct prng_context {
 45         spinlock_t prng_lock;
 46         unsigned char rand_data[DEFAULT_BLK_SZ];
 47         unsigned char last_rand_data[DEFAULT_BLK_SZ];
 48         unsigned char DT[DEFAULT_BLK_SZ];
 49         unsigned char I[DEFAULT_BLK_SZ];
 50         unsigned char V[DEFAULT_BLK_SZ];
 51         u32 rand_data_valid;
 52         struct crypto_cipher *tfm;
 53         u32 flags;
 54 };
 55 
 56 static int dbg;
 57 
 58 static void hexdump(char *note, unsigned char *buf, unsigned int len)
 59 {
 60         if (dbg) {
 61                 printk(KERN_CRIT "%s", note);
 62                 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
 63                                 16, 1,
 64                                 buf, len, false);
 65         }
 66 }
 67 
 68 #define dbgprint(format, args...) do {\
 69 if (dbg)\
 70         printk(format, ##args);\
 71 } while (0)
 72 
 73 static void xor_vectors(unsigned char *in1, unsigned char *in2,
 74                         unsigned char *out, unsigned int size)
 75 {
 76         int i;
 77 
 78         for (i = 0; i < size; i++)
 79                 out[i] = in1[i] ^ in2[i];
 80 
 81 }
 82 /*
 83  * Returns DEFAULT_BLK_SZ bytes of random data per call
 84  * returns 0 if generation succeeded, <0 if something went wrong
 85  */
 86 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
 87 {
 88         int i;
 89         unsigned char tmp[DEFAULT_BLK_SZ];
 90         unsigned char *output = NULL;
 91 
 92 
 93         dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
 94                 ctx);
 95 
 96         hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
 97         hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
 98         hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
 99 
100         /*
101          * This algorithm is a 3 stage state machine
102          */
103         for (i = 0; i < 3; i++) {
104 
105                 switch (i) {
106                 case 0:
107                         /*
108                          * Start by encrypting the counter value
109                          * This gives us an intermediate value I
110                          */
111                         memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
112                         output = ctx->I;
113                         hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
114                         break;
115                 case 1:
116 
117                         /*
118                          * Next xor I with our secret vector V
119                          * encrypt that result to obtain our
120                          * pseudo random data which we output
121                          */
122                         xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
123                         hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
124                         output = ctx->rand_data;
125                         break;
126                 case 2:
127                         /*
128                          * First check that we didn't produce the same
129                          * random data that we did last time around through this
130                          */
131                         if (!memcmp(ctx->rand_data, ctx->last_rand_data,
132                                         DEFAULT_BLK_SZ)) {
133                                 if (cont_test) {
134                                         panic("cprng %p Failed repetition check!\n",
135                                                 ctx);
136                                 }
137 
138                                 printk(KERN_ERR
139                                         "ctx %p Failed repetition check!\n",
140                                         ctx);
141 
142                                 ctx->flags |= PRNG_NEED_RESET;
143                                 return -EINVAL;
144                         }
145                         memcpy(ctx->last_rand_data, ctx->rand_data,
146                                 DEFAULT_BLK_SZ);
147 
148                         /*
149                          * Lastly xor the random data with I
150                          * and encrypt that to obtain a new secret vector V
151                          */
152                         xor_vectors(ctx->rand_data, ctx->I, tmp,
153                                 DEFAULT_BLK_SZ);
154                         output = ctx->V;
155                         hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
156                         break;
157                 }
158 
159 
160                 /* do the encryption */
161                 crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
162 
163         }
164 
165         /*
166          * Now update our DT value
167          */
168         for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
169                 ctx->DT[i] += 1;
170                 if (ctx->DT[i] != 0)
171                         break;
172         }
173 
174         dbgprint("Returning new block for context %p\n", ctx);
175         ctx->rand_data_valid = 0;
176 
177         hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
178         hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
179         hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
180         hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
181 
182         return 0;
183 }
184 
185 /* Our exported functions */
186 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
187                                 int do_cont_test)
188 {
189         unsigned char *ptr = buf;
190         unsigned int byte_count = (unsigned int)nbytes;
191         int err;
192 
193 
194         spin_lock_bh(&ctx->prng_lock);
195 
196         err = -EINVAL;
197         if (ctx->flags & PRNG_NEED_RESET)
198                 goto done;
199 
200         /*
201          * If the FIXED_SIZE flag is on, only return whole blocks of
202          * pseudo random data
203          */
204         err = -EINVAL;
205         if (ctx->flags & PRNG_FIXED_SIZE) {
206                 if (nbytes < DEFAULT_BLK_SZ)
207                         goto done;
208                 byte_count = DEFAULT_BLK_SZ;
209         }
210 
211         /*
212          * Return 0 in case of success as mandated by the kernel
213          * crypto API interface definition.
214          */
215         err = 0;
216 
217         dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
218                 byte_count, ctx);
219 
220 
221 remainder:
222         if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
223                 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
224                         memset(buf, 0, nbytes);
225                         err = -EINVAL;
226                         goto done;
227                 }
228         }
229 
230         /*
231          * Copy any data less than an entire block
232          */
233         if (byte_count < DEFAULT_BLK_SZ) {
234 empty_rbuf:
235                 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
236                         *ptr = ctx->rand_data[ctx->rand_data_valid];
237                         ptr++;
238                         byte_count--;
239                         ctx->rand_data_valid++;
240                         if (byte_count == 0)
241                                 goto done;
242                 }
243         }
244 
245         /*
246          * Now copy whole blocks
247          */
248         for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
249                 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
250                         if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
251                                 memset(buf, 0, nbytes);
252                                 err = -EINVAL;
253                                 goto done;
254                         }
255                 }
256                 if (ctx->rand_data_valid > 0)
257                         goto empty_rbuf;
258                 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
259                 ctx->rand_data_valid += DEFAULT_BLK_SZ;
260                 ptr += DEFAULT_BLK_SZ;
261         }
262 
263         /*
264          * Now go back and get any remaining partial block
265          */
266         if (byte_count)
267                 goto remainder;
268 
269 done:
270         spin_unlock_bh(&ctx->prng_lock);
271         dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
272                 err, ctx);
273         return err;
274 }
275 
276 static void free_prng_context(struct prng_context *ctx)
277 {
278         crypto_free_cipher(ctx->tfm);
279 }
280 
281 static int reset_prng_context(struct prng_context *ctx,
282                               const unsigned char *key, size_t klen,
283                               const unsigned char *V, const unsigned char *DT)
284 {
285         int ret;
286         const unsigned char *prng_key;
287 
288         spin_lock_bh(&ctx->prng_lock);
289         ctx->flags |= PRNG_NEED_RESET;
290 
291         prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
292 
293         if (!key)
294                 klen = DEFAULT_PRNG_KSZ;
295 
296         if (V)
297                 memcpy(ctx->V, V, DEFAULT_BLK_SZ);
298         else
299                 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
300 
301         if (DT)
302                 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
303         else
304                 memset(ctx->DT, 0, DEFAULT_BLK_SZ);
305 
306         memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
307         memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
308 
309         ctx->rand_data_valid = DEFAULT_BLK_SZ;
310 
311         ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
312         if (ret) {
313                 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
314                         crypto_cipher_get_flags(ctx->tfm));
315                 goto out;
316         }
317 
318         ret = 0;
319         ctx->flags &= ~PRNG_NEED_RESET;
320 out:
321         spin_unlock_bh(&ctx->prng_lock);
322         return ret;
323 }
324 
325 static int cprng_init(struct crypto_tfm *tfm)
326 {
327         struct prng_context *ctx = crypto_tfm_ctx(tfm);
328 
329         spin_lock_init(&ctx->prng_lock);
330         ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
331         if (IS_ERR(ctx->tfm)) {
332                 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
333                                 ctx);
334                 return PTR_ERR(ctx->tfm);
335         }
336 
337         if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
338                 return -EINVAL;
339 
340         /*
341          * after allocation, we should always force the user to reset
342          * so they don't inadvertently use the insecure default values
343          * without specifying them intentially
344          */
345         ctx->flags |= PRNG_NEED_RESET;
346         return 0;
347 }
348 
349 static void cprng_exit(struct crypto_tfm *tfm)
350 {
351         free_prng_context(crypto_tfm_ctx(tfm));
352 }
353 
354 static int cprng_get_random(struct crypto_rng *tfm,
355                             const u8 *src, unsigned int slen,
356                             u8 *rdata, unsigned int dlen)
357 {
358         struct prng_context *prng = crypto_rng_ctx(tfm);
359 
360         return get_prng_bytes(rdata, dlen, prng, 0);
361 }
362 
363 /*
364  *  This is the cprng_registered reset method the seed value is
365  *  interpreted as the tuple { V KEY DT}
366  *  V and KEY are required during reset, and DT is optional, detected
367  *  as being present by testing the length of the seed
368  */
369 static int cprng_reset(struct crypto_rng *tfm,
370                        const u8 *seed, unsigned int slen)
371 {
372         struct prng_context *prng = crypto_rng_ctx(tfm);
373         const u8 *key = seed + DEFAULT_BLK_SZ;
374         const u8 *dt = NULL;
375 
376         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
377                 return -EINVAL;
378 
379         if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
380                 dt = key + DEFAULT_PRNG_KSZ;
381 
382         reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
383 
384         if (prng->flags & PRNG_NEED_RESET)
385                 return -EINVAL;
386         return 0;
387 }
388 
389 #ifdef CONFIG_CRYPTO_FIPS
390 static int fips_cprng_get_random(struct crypto_rng *tfm,
391                                  const u8 *src, unsigned int slen,
392                                  u8 *rdata, unsigned int dlen)
393 {
394         struct prng_context *prng = crypto_rng_ctx(tfm);
395 
396         return get_prng_bytes(rdata, dlen, prng, 1);
397 }
398 
399 static int fips_cprng_reset(struct crypto_rng *tfm,
400                             const u8 *seed, unsigned int slen)
401 {
402         u8 rdata[DEFAULT_BLK_SZ];
403         const u8 *key = seed + DEFAULT_BLK_SZ;
404         int rc;
405 
406         struct prng_context *prng = crypto_rng_ctx(tfm);
407 
408         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
409                 return -EINVAL;
410 
411         /* fips strictly requires seed != key */
412         if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
413                 return -EINVAL;
414 
415         rc = cprng_reset(tfm, seed, slen);
416 
417         if (!rc)
418                 goto out;
419 
420         /* this primes our continuity test */
421         rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
422         prng->rand_data_valid = DEFAULT_BLK_SZ;
423 
424 out:
425         return rc;
426 }
427 #endif
428 
429 static struct rng_alg rng_algs[] = { {
430         .generate               = cprng_get_random,
431         .seed                   = cprng_reset,
432         .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
433         .base                   =       {
434                 .cra_name               = "stdrng",
435                 .cra_driver_name        = "ansi_cprng",
436                 .cra_priority           = 100,
437                 .cra_ctxsize            = sizeof(struct prng_context),
438                 .cra_module             = THIS_MODULE,
439                 .cra_init               = cprng_init,
440                 .cra_exit               = cprng_exit,
441         }
442 #ifdef CONFIG_CRYPTO_FIPS
443 }, {
444         .generate               = fips_cprng_get_random,
445         .seed                   = fips_cprng_reset,
446         .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
447         .base                   =       {
448                 .cra_name               = "fips(ansi_cprng)",
449                 .cra_driver_name        = "fips_ansi_cprng",
450                 .cra_priority           = 300,
451                 .cra_ctxsize            = sizeof(struct prng_context),
452                 .cra_module             = THIS_MODULE,
453                 .cra_init               = cprng_init,
454                 .cra_exit               = cprng_exit,
455         }
456 #endif
457 } };
458 
459 /* Module initalization */
460 static int __init prng_mod_init(void)
461 {
462         return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
463 }
464 
465 static void __exit prng_mod_fini(void)
466 {
467         crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
468 }
469 
470 MODULE_LICENSE("GPL");
471 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
472 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
473 module_param(dbg, int, 0);
474 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
475 module_init(prng_mod_init);
476 module_exit(prng_mod_fini);
477 MODULE_ALIAS_CRYPTO("stdrng");
478 MODULE_ALIAS_CRYPTO("ansi_cprng");
479 

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