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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 | |
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 | |
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 succeded, <0 if something went wrong |
87 | */ |
88 | static int _get_more_prng_bytes(struct prng_context *ctx) |
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 (fips_enabled) { |
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 */ |
188 | static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx) |
189 | { |
190 | unsigned char *ptr = buf; |
191 | unsigned int byte_count = (unsigned int)nbytes; |
192 | int err; |
193 | |
194 | |
195 | if (nbytes < 0) |
196 | return -EINVAL; |
197 | |
198 | spin_lock_bh(&ctx->prng_lock); |
199 | |
200 | err = -EINVAL; |
201 | if (ctx->flags & PRNG_NEED_RESET) |
202 | goto done; |
203 | |
204 | /* |
205 | * If the FIXED_SIZE flag is on, only return whole blocks of |
206 | * pseudo random data |
207 | */ |
208 | err = -EINVAL; |
209 | if (ctx->flags & PRNG_FIXED_SIZE) { |
210 | if (nbytes < DEFAULT_BLK_SZ) |
211 | goto done; |
212 | byte_count = DEFAULT_BLK_SZ; |
213 | } |
214 | |
215 | err = byte_count; |
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) < 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 | for (; ctx->rand_data_valid < DEFAULT_BLK_SZ; |
236 | ctx->rand_data_valid++) { |
237 | *ptr = ctx->rand_data[ctx->rand_data_valid]; |
238 | ptr++; |
239 | byte_count--; |
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) < 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 | unsigned char *key, size_t klen, |
283 | unsigned char *V, unsigned char *DT) |
284 | { |
285 | int ret; |
286 | 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, u8 *rdata, |
355 | unsigned int dlen) |
356 | { |
357 | struct prng_context *prng = crypto_rng_ctx(tfm); |
358 | |
359 | return get_prng_bytes(rdata, dlen, prng); |
360 | } |
361 | |
362 | /* |
363 | * This is the cprng_registered reset method the seed value is |
364 | * interpreted as the tuple { V KEY DT} |
365 | * V and KEY are required during reset, and DT is optional, detected |
366 | * as being present by testing the length of the seed |
367 | */ |
368 | static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen) |
369 | { |
370 | struct prng_context *prng = crypto_rng_ctx(tfm); |
371 | u8 *key = seed + DEFAULT_BLK_SZ; |
372 | u8 *dt = NULL; |
373 | |
374 | if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) |
375 | return -EINVAL; |
376 | |
377 | if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ)) |
378 | dt = key + DEFAULT_PRNG_KSZ; |
379 | |
380 | reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt); |
381 | |
382 | if (prng->flags & PRNG_NEED_RESET) |
383 | return -EINVAL; |
384 | return 0; |
385 | } |
386 | |
387 | static struct crypto_alg rng_alg = { |
388 | .cra_name = "stdrng", |
389 | .cra_driver_name = "ansi_cprng", |
390 | .cra_priority = 100, |
391 | .cra_flags = CRYPTO_ALG_TYPE_RNG, |
392 | .cra_ctxsize = sizeof(struct prng_context), |
393 | .cra_type = &crypto_rng_type, |
394 | .cra_module = THIS_MODULE, |
395 | .cra_list = LIST_HEAD_INIT(rng_alg.cra_list), |
396 | .cra_init = cprng_init, |
397 | .cra_exit = cprng_exit, |
398 | .cra_u = { |
399 | .rng = { |
400 | .rng_make_random = cprng_get_random, |
401 | .rng_reset = cprng_reset, |
402 | .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ, |
403 | } |
404 | } |
405 | }; |
406 | |
407 | |
408 | /* Module initalization */ |
409 | static int __init prng_mod_init(void) |
410 | { |
411 | if (fips_enabled) |
412 | rng_alg.cra_priority += 200; |
413 | |
414 | return crypto_register_alg(&rng_alg); |
415 | } |
416 | |
417 | static void __exit prng_mod_fini(void) |
418 | { |
419 | crypto_unregister_alg(&rng_alg); |
420 | return; |
421 | } |
422 | |
423 | MODULE_LICENSE("GPL"); |
424 | MODULE_DESCRIPTION("Software Pseudo Random Number Generator"); |
425 | MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>"); |
426 | module_param(dbg, int, 0); |
427 | MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)"); |
428 | module_init(prng_mod_init); |
429 | module_exit(prng_mod_fini); |
430 | MODULE_ALIAS("stdrng"); |
431 |
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