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 #include "internal.h"
24
25 #define DEFAULT_PRNG_KEY "0123456789abcdef"
26 #define DEFAULT_PRNG_KSZ 16
27 #define DEFAULT_BLK_SZ 16
28 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
29
30 /*
31 * Flags for the prng_context flags field
32 */
33
34 #define PRNG_FIXED_SIZE 0x1
35 #define PRNG_NEED_RESET 0x2
36
37 /*
38 * Note: DT is our counter value
39 * I is our intermediate value
40 * V is our seed vector
41 * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
42 * for implementation details
43 */
44
45
46 struct prng_context {
47 spinlock_t prng_lock;
48 unsigned char rand_data[DEFAULT_BLK_SZ];
49 unsigned char last_rand_data[DEFAULT_BLK_SZ];
50 unsigned char DT[DEFAULT_BLK_SZ];
51 unsigned char I[DEFAULT_BLK_SZ];
52 unsigned char V[DEFAULT_BLK_SZ];
53 u32 rand_data_valid;
54 struct crypto_cipher *tfm;
55 u32 flags;
56 };
57
58 static int dbg;
59
hexdump(char * note,unsigned char * buf,unsigned int len)60 static void hexdump(char *note, unsigned char *buf, unsigned int len)
61 {
62 if (dbg) {
63 printk(KERN_CRIT "%s", note);
64 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
65 16, 1,
66 buf, len, false);
67 }
68 }
69
70 #define dbgprint(format, args...) do {\
71 if (dbg)\
72 printk(format, ##args);\
73 } while (0)
74
xor_vectors(unsigned char * in1,unsigned char * in2,unsigned char * out,unsigned int size)75 static void xor_vectors(unsigned char *in1, unsigned char *in2,
76 unsigned char *out, unsigned int size)
77 {
78 int i;
79
80 for (i = 0; i < size; i++)
81 out[i] = in1[i] ^ in2[i];
82
83 }
84 /*
85 * Returns DEFAULT_BLK_SZ bytes of random data per call
86 * returns 0 if generation succeeded, <0 if something went wrong
87 */
_get_more_prng_bytes(struct prng_context * ctx,int cont_test)88 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
89 {
90 int i;
91 unsigned char tmp[DEFAULT_BLK_SZ];
92 unsigned char *output = NULL;
93
94
95 dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
96 ctx);
97
98 hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
99 hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
100 hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
101
102 /*
103 * This algorithm is a 3 stage state machine
104 */
105 for (i = 0; i < 3; i++) {
106
107 switch (i) {
108 case 0:
109 /*
110 * Start by encrypting the counter value
111 * This gives us an intermediate value I
112 */
113 memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
114 output = ctx->I;
115 hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
116 break;
117 case 1:
118
119 /*
120 * Next xor I with our secret vector V
121 * encrypt that result to obtain our
122 * pseudo random data which we output
123 */
124 xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
125 hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
126 output = ctx->rand_data;
127 break;
128 case 2:
129 /*
130 * First check that we didn't produce the same
131 * random data that we did last time around through this
132 */
133 if (!memcmp(ctx->rand_data, ctx->last_rand_data,
134 DEFAULT_BLK_SZ)) {
135 if (cont_test) {
136 panic("cprng %p Failed repetition check!\n",
137 ctx);
138 }
139
140 printk(KERN_ERR
141 "ctx %p Failed repetition check!\n",
142 ctx);
143
144 ctx->flags |= PRNG_NEED_RESET;
145 return -EINVAL;
146 }
147 memcpy(ctx->last_rand_data, ctx->rand_data,
148 DEFAULT_BLK_SZ);
149
150 /*
151 * Lastly xor the random data with I
152 * and encrypt that to obtain a new secret vector V
153 */
154 xor_vectors(ctx->rand_data, ctx->I, tmp,
155 DEFAULT_BLK_SZ);
156 output = ctx->V;
157 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
158 break;
159 }
160
161
162 /* do the encryption */
163 crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
164
165 }
166
167 /*
168 * Now update our DT value
169 */
170 for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
171 ctx->DT[i] += 1;
172 if (ctx->DT[i] != 0)
173 break;
174 }
175
176 dbgprint("Returning new block for context %p\n", ctx);
177 ctx->rand_data_valid = 0;
178
179 hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
180 hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
181 hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
182 hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
183
184 return 0;
185 }
186
187 /* Our exported functions */
get_prng_bytes(char * buf,size_t nbytes,struct prng_context * ctx,int do_cont_test)188 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
189 int do_cont_test)
190 {
191 unsigned char *ptr = buf;
192 unsigned int byte_count = (unsigned int)nbytes;
193 int err;
194
195
196 spin_lock_bh(&ctx->prng_lock);
197
198 err = -EINVAL;
199 if (ctx->flags & PRNG_NEED_RESET)
200 goto done;
201
202 /*
203 * If the FIXED_SIZE flag is on, only return whole blocks of
204 * pseudo random data
205 */
206 err = -EINVAL;
207 if (ctx->flags & PRNG_FIXED_SIZE) {
208 if (nbytes < DEFAULT_BLK_SZ)
209 goto done;
210 byte_count = DEFAULT_BLK_SZ;
211 }
212
213 err = byte_count;
214
215 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
216 byte_count, ctx);
217
218
219 remainder:
220 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
221 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
222 memset(buf, 0, nbytes);
223 err = -EINVAL;
224 goto done;
225 }
226 }
227
228 /*
229 * Copy any data less than an entire block
230 */
231 if (byte_count < DEFAULT_BLK_SZ) {
232 empty_rbuf:
233 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
234 *ptr = ctx->rand_data[ctx->rand_data_valid];
235 ptr++;
236 byte_count--;
237 ctx->rand_data_valid++;
238 if (byte_count == 0)
239 goto done;
240 }
241 }
242
243 /*
244 * Now copy whole blocks
245 */
246 for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
247 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
248 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
249 memset(buf, 0, nbytes);
250 err = -EINVAL;
251 goto done;
252 }
253 }
254 if (ctx->rand_data_valid > 0)
255 goto empty_rbuf;
256 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
257 ctx->rand_data_valid += DEFAULT_BLK_SZ;
258 ptr += DEFAULT_BLK_SZ;
259 }
260
261 /*
262 * Now go back and get any remaining partial block
263 */
264 if (byte_count)
265 goto remainder;
266
267 done:
268 spin_unlock_bh(&ctx->prng_lock);
269 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
270 err, ctx);
271 return err;
272 }
273
free_prng_context(struct prng_context * ctx)274 static void free_prng_context(struct prng_context *ctx)
275 {
276 crypto_free_cipher(ctx->tfm);
277 }
278
reset_prng_context(struct prng_context * ctx,unsigned char * key,size_t klen,unsigned char * V,unsigned char * DT)279 static int reset_prng_context(struct prng_context *ctx,
280 unsigned char *key, size_t klen,
281 unsigned char *V, unsigned char *DT)
282 {
283 int ret;
284 unsigned char *prng_key;
285
286 spin_lock_bh(&ctx->prng_lock);
287 ctx->flags |= PRNG_NEED_RESET;
288
289 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
290
291 if (!key)
292 klen = DEFAULT_PRNG_KSZ;
293
294 if (V)
295 memcpy(ctx->V, V, DEFAULT_BLK_SZ);
296 else
297 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
298
299 if (DT)
300 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
301 else
302 memset(ctx->DT, 0, DEFAULT_BLK_SZ);
303
304 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
305 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
306
307 ctx->rand_data_valid = DEFAULT_BLK_SZ;
308
309 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
310 if (ret) {
311 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
312 crypto_cipher_get_flags(ctx->tfm));
313 goto out;
314 }
315
316 ret = 0;
317 ctx->flags &= ~PRNG_NEED_RESET;
318 out:
319 spin_unlock_bh(&ctx->prng_lock);
320 return ret;
321 }
322
cprng_init(struct crypto_tfm * tfm)323 static int cprng_init(struct crypto_tfm *tfm)
324 {
325 struct prng_context *ctx = crypto_tfm_ctx(tfm);
326
327 spin_lock_init(&ctx->prng_lock);
328 ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
329 if (IS_ERR(ctx->tfm)) {
330 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
331 ctx);
332 return PTR_ERR(ctx->tfm);
333 }
334
335 if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
336 return -EINVAL;
337
338 /*
339 * after allocation, we should always force the user to reset
340 * so they don't inadvertently use the insecure default values
341 * without specifying them intentially
342 */
343 ctx->flags |= PRNG_NEED_RESET;
344 return 0;
345 }
346
cprng_exit(struct crypto_tfm * tfm)347 static void cprng_exit(struct crypto_tfm *tfm)
348 {
349 free_prng_context(crypto_tfm_ctx(tfm));
350 }
351
cprng_get_random(struct crypto_rng * tfm,u8 * rdata,unsigned int dlen)352 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
353 unsigned int dlen)
354 {
355 struct prng_context *prng = crypto_rng_ctx(tfm);
356
357 return get_prng_bytes(rdata, dlen, prng, 0);
358 }
359
360 /*
361 * This is the cprng_registered reset method the seed value is
362 * interpreted as the tuple { V KEY DT}
363 * V and KEY are required during reset, and DT is optional, detected
364 * as being present by testing the length of the seed
365 */
cprng_reset(struct crypto_rng * tfm,u8 * seed,unsigned int slen)366 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
367 {
368 struct prng_context *prng = crypto_rng_ctx(tfm);
369 u8 *key = seed + DEFAULT_BLK_SZ;
370 u8 *dt = NULL;
371
372 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
373 return -EINVAL;
374
375 if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
376 dt = key + DEFAULT_PRNG_KSZ;
377
378 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
379
380 if (prng->flags & PRNG_NEED_RESET)
381 return -EINVAL;
382 return 0;
383 }
384
385 static struct crypto_alg rng_alg = {
386 .cra_name = "stdrng",
387 .cra_driver_name = "ansi_cprng",
388 .cra_priority = 100,
389 .cra_flags = CRYPTO_ALG_TYPE_RNG,
390 .cra_ctxsize = sizeof(struct prng_context),
391 .cra_type = &crypto_rng_type,
392 .cra_module = THIS_MODULE,
393 .cra_list = LIST_HEAD_INIT(rng_alg.cra_list),
394 .cra_init = cprng_init,
395 .cra_exit = cprng_exit,
396 .cra_u = {
397 .rng = {
398 .rng_make_random = cprng_get_random,
399 .rng_reset = cprng_reset,
400 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
401 }
402 }
403 };
404
405 #ifdef CONFIG_CRYPTO_FIPS
fips_cprng_get_random(struct crypto_rng * tfm,u8 * rdata,unsigned int dlen)406 static int fips_cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
407 unsigned int dlen)
408 {
409 struct prng_context *prng = crypto_rng_ctx(tfm);
410
411 return get_prng_bytes(rdata, dlen, prng, 1);
412 }
413
fips_cprng_reset(struct crypto_rng * tfm,u8 * seed,unsigned int slen)414 static int fips_cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
415 {
416 u8 rdata[DEFAULT_BLK_SZ];
417 u8 *key = seed + DEFAULT_BLK_SZ;
418 int rc;
419
420 struct prng_context *prng = crypto_rng_ctx(tfm);
421
422 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
423 return -EINVAL;
424
425 /* fips strictly requires seed != key */
426 if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
427 return -EINVAL;
428
429 rc = cprng_reset(tfm, seed, slen);
430
431 if (!rc)
432 goto out;
433
434 /* this primes our continuity test */
435 rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
436 prng->rand_data_valid = DEFAULT_BLK_SZ;
437
438 out:
439 return rc;
440 }
441
442 static struct crypto_alg fips_rng_alg = {
443 .cra_name = "fips(ansi_cprng)",
444 .cra_driver_name = "fips_ansi_cprng",
445 .cra_priority = 300,
446 .cra_flags = CRYPTO_ALG_TYPE_RNG,
447 .cra_ctxsize = sizeof(struct prng_context),
448 .cra_type = &crypto_rng_type,
449 .cra_module = THIS_MODULE,
450 .cra_list = LIST_HEAD_INIT(rng_alg.cra_list),
451 .cra_init = cprng_init,
452 .cra_exit = cprng_exit,
453 .cra_u = {
454 .rng = {
455 .rng_make_random = fips_cprng_get_random,
456 .rng_reset = fips_cprng_reset,
457 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
458 }
459 }
460 };
461 #endif
462
463 /* Module initalization */
prng_mod_init(void)464 static int __init prng_mod_init(void)
465 {
466 int rc = 0;
467
468 rc = crypto_register_alg(&rng_alg);
469 #ifdef CONFIG_CRYPTO_FIPS
470 if (rc)
471 goto out;
472
473 rc = crypto_register_alg(&fips_rng_alg);
474
475 out:
476 #endif
477 return rc;
478 }
479
prng_mod_fini(void)480 static void __exit prng_mod_fini(void)
481 {
482 crypto_unregister_alg(&rng_alg);
483 #ifdef CONFIG_CRYPTO_FIPS
484 crypto_unregister_alg(&fips_rng_alg);
485 #endif
486 return;
487 }
488
489 MODULE_LICENSE("GPL");
490 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
491 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
492 module_param(dbg, int, 0);
493 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
494 module_init(prng_mod_init);
495 module_exit(prng_mod_fini);
496 MODULE_ALIAS("stdrng");
497