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 succeded, <0 if something went wrong
87 */
_get_more_prng_bytes(struct prng_context * ctx)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 printk(KERN_ERR
136 "ctx %p Failed repetition check!\n",
137 ctx);
138 ctx->flags |= PRNG_NEED_RESET;
139 return -EINVAL;
140 }
141 memcpy(ctx->last_rand_data, ctx->rand_data,
142 DEFAULT_BLK_SZ);
143
144 /*
145 * Lastly xor the random data with I
146 * and encrypt that to obtain a new secret vector V
147 */
148 xor_vectors(ctx->rand_data, ctx->I, tmp,
149 DEFAULT_BLK_SZ);
150 output = ctx->V;
151 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
152 break;
153 }
154
155
156 /* do the encryption */
157 crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
158
159 }
160
161 /*
162 * Now update our DT value
163 */
164 for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
165 ctx->DT[i] += 1;
166 if (ctx->DT[i] != 0)
167 break;
168 }
169
170 dbgprint("Returning new block for context %p\n", ctx);
171 ctx->rand_data_valid = 0;
172
173 hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
174 hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
175 hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
176 hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
177
178 return 0;
179 }
180
181 /* Our exported functions */
get_prng_bytes(char * buf,size_t nbytes,struct prng_context * ctx)182 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx)
183 {
184 unsigned long flags;
185 unsigned char *ptr = buf;
186 unsigned int byte_count = (unsigned int)nbytes;
187 int err;
188
189
190 if (nbytes < 0)
191 return -EINVAL;
192
193 spin_lock_irqsave(&ctx->prng_lock, flags);
194
195 err = -EINVAL;
196 if (ctx->flags & PRNG_NEED_RESET)
197 goto done;
198
199 /*
200 * If the FIXED_SIZE flag is on, only return whole blocks of
201 * pseudo random data
202 */
203 err = -EINVAL;
204 if (ctx->flags & PRNG_FIXED_SIZE) {
205 if (nbytes < DEFAULT_BLK_SZ)
206 goto done;
207 byte_count = DEFAULT_BLK_SZ;
208 }
209
210 err = byte_count;
211
212 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
213 byte_count, ctx);
214
215
216 remainder:
217 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
218 if (_get_more_prng_bytes(ctx) < 0) {
219 memset(buf, 0, nbytes);
220 err = -EINVAL;
221 goto done;
222 }
223 }
224
225 /*
226 * Copy any data less than an entire block
227 */
228 if (byte_count < DEFAULT_BLK_SZ) {
229 empty_rbuf:
230 for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
231 ctx->rand_data_valid++) {
232 *ptr = ctx->rand_data[ctx->rand_data_valid];
233 ptr++;
234 byte_count--;
235 if (byte_count == 0)
236 goto done;
237 }
238 }
239
240 /*
241 * Now copy whole blocks
242 */
243 for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
244 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
245 if (_get_more_prng_bytes(ctx) < 0) {
246 memset(buf, 0, nbytes);
247 err = -EINVAL;
248 goto done;
249 }
250 }
251 if (ctx->rand_data_valid > 0)
252 goto empty_rbuf;
253 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
254 ctx->rand_data_valid += DEFAULT_BLK_SZ;
255 ptr += DEFAULT_BLK_SZ;
256 }
257
258 /*
259 * Now go back and get any remaining partial block
260 */
261 if (byte_count)
262 goto remainder;
263
264 done:
265 spin_unlock_irqrestore(&ctx->prng_lock, flags);
266 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
267 err, ctx);
268 return err;
269 }
270
free_prng_context(struct prng_context * ctx)271 static void free_prng_context(struct prng_context *ctx)
272 {
273 crypto_free_cipher(ctx->tfm);
274 }
275
reset_prng_context(struct prng_context * ctx,unsigned char * key,size_t klen,unsigned char * V,unsigned char * DT)276 static int reset_prng_context(struct prng_context *ctx,
277 unsigned char *key, size_t klen,
278 unsigned char *V, unsigned char *DT)
279 {
280 int ret;
281 int rc = -EINVAL;
282 unsigned char *prng_key;
283
284 spin_lock(&ctx->prng_lock);
285 ctx->flags |= PRNG_NEED_RESET;
286
287 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
288
289 if (!key)
290 klen = DEFAULT_PRNG_KSZ;
291
292 if (V)
293 memcpy(ctx->V, V, DEFAULT_BLK_SZ);
294 else
295 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
296
297 if (DT)
298 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
299 else
300 memset(ctx->DT, 0, DEFAULT_BLK_SZ);
301
302 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
303 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
304
305 if (ctx->tfm)
306 crypto_free_cipher(ctx->tfm);
307
308 ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
309 if (IS_ERR(ctx->tfm)) {
310 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
311 ctx);
312 ctx->tfm = NULL;
313 goto out;
314 }
315
316 ctx->rand_data_valid = DEFAULT_BLK_SZ;
317
318 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
319 if (ret) {
320 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
321 crypto_cipher_get_flags(ctx->tfm));
322 crypto_free_cipher(ctx->tfm);
323 goto out;
324 }
325
326 rc = 0;
327 ctx->flags &= ~PRNG_NEED_RESET;
328 out:
329 spin_unlock(&ctx->prng_lock);
330
331 return rc;
332
333 }
334
cprng_init(struct crypto_tfm * tfm)335 static int cprng_init(struct crypto_tfm *tfm)
336 {
337 struct prng_context *ctx = crypto_tfm_ctx(tfm);
338
339 spin_lock_init(&ctx->prng_lock);
340
341 return reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL);
342 }
343
cprng_exit(struct crypto_tfm * tfm)344 static void cprng_exit(struct crypto_tfm *tfm)
345 {
346 free_prng_context(crypto_tfm_ctx(tfm));
347 }
348
cprng_get_random(struct crypto_rng * tfm,u8 * rdata,unsigned int dlen)349 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
350 unsigned int dlen)
351 {
352 struct prng_context *prng = crypto_rng_ctx(tfm);
353
354 return get_prng_bytes(rdata, dlen, prng);
355 }
356
357 /*
358 * This is the cprng_registered reset method the seed value is
359 * interpreted as the tuple { V KEY DT}
360 * V and KEY are required during reset, and DT is optional, detected
361 * as being present by testing the length of the seed
362 */
cprng_reset(struct crypto_rng * tfm,u8 * seed,unsigned int slen)363 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
364 {
365 struct prng_context *prng = crypto_rng_ctx(tfm);
366 u8 *key = seed + DEFAULT_BLK_SZ;
367 u8 *dt = NULL;
368
369 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
370 return -EINVAL;
371
372 if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
373 dt = key + DEFAULT_PRNG_KSZ;
374
375 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
376
377 if (prng->flags & PRNG_NEED_RESET)
378 return -EINVAL;
379 return 0;
380 }
381
382 static struct crypto_alg rng_alg = {
383 .cra_name = "stdrng",
384 .cra_driver_name = "ansi_cprng",
385 .cra_priority = 100,
386 .cra_flags = CRYPTO_ALG_TYPE_RNG,
387 .cra_ctxsize = sizeof(struct prng_context),
388 .cra_type = &crypto_rng_type,
389 .cra_module = THIS_MODULE,
390 .cra_list = LIST_HEAD_INIT(rng_alg.cra_list),
391 .cra_init = cprng_init,
392 .cra_exit = cprng_exit,
393 .cra_u = {
394 .rng = {
395 .rng_make_random = cprng_get_random,
396 .rng_reset = cprng_reset,
397 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
398 }
399 }
400 };
401
402
403 /* Module initalization */
prng_mod_init(void)404 static int __init prng_mod_init(void)
405 {
406 int ret = 0;
407
408 if (fips_enabled)
409 rng_alg.cra_priority += 200;
410
411 ret = crypto_register_alg(&rng_alg);
412
413 if (ret)
414 goto out;
415 out:
416 return 0;
417 }
418
prng_mod_fini(void)419 static void __exit prng_mod_fini(void)
420 {
421 crypto_unregister_alg(&rng_alg);
422 return;
423 }
424
425 MODULE_LICENSE("GPL");
426 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
427 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
428 module_param(dbg, int, 0);
429 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
430 module_init(prng_mod_init);
431 module_exit(prng_mod_fini);
432 MODULE_ALIAS("stdrng");
433