xref: /openbmc/linux/crypto/ansi_cprng.c (revision 8fdff1dc) 
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 succeeded, <0 if something went wrong
87  */
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 */
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 		for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
234 			ctx->rand_data_valid++) {
235 			*ptr = ctx->rand_data[ctx->rand_data_valid];
236 			ptr++;
237 			byte_count--;
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 
274 static void free_prng_context(struct prng_context *ctx)
275 {
276 	crypto_free_cipher(ctx->tfm);
277 }
278 
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 
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 
347 static void cprng_exit(struct crypto_tfm *tfm)
348 {
349 	free_prng_context(crypto_tfm_ctx(tfm));
350 }
351 
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  */
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 #ifdef CONFIG_CRYPTO_FIPS
386 static int fips_cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
387 			    unsigned int dlen)
388 {
389 	struct prng_context *prng = crypto_rng_ctx(tfm);
390 
391 	return get_prng_bytes(rdata, dlen, prng, 1);
392 }
393 
394 static int fips_cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
395 {
396 	u8 rdata[DEFAULT_BLK_SZ];
397 	u8 *key = seed + DEFAULT_BLK_SZ;
398 	int rc;
399 
400 	struct prng_context *prng = crypto_rng_ctx(tfm);
401 
402 	if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
403 		return -EINVAL;
404 
405 	/* fips strictly requires seed != key */
406 	if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
407 		return -EINVAL;
408 
409 	rc = cprng_reset(tfm, seed, slen);
410 
411 	if (!rc)
412 		goto out;
413 
414 	/* this primes our continuity test */
415 	rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
416 	prng->rand_data_valid = DEFAULT_BLK_SZ;
417 
418 out:
419 	return rc;
420 }
421 #endif
422 
423 static struct crypto_alg rng_algs[] = { {
424 	.cra_name		= "stdrng",
425 	.cra_driver_name	= "ansi_cprng",
426 	.cra_priority		= 100,
427 	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
428 	.cra_ctxsize		= sizeof(struct prng_context),
429 	.cra_type		= &crypto_rng_type,
430 	.cra_module		= THIS_MODULE,
431 	.cra_init		= cprng_init,
432 	.cra_exit		= cprng_exit,
433 	.cra_u			= {
434 		.rng = {
435 			.rng_make_random	= cprng_get_random,
436 			.rng_reset		= cprng_reset,
437 			.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
438 		}
439 	}
440 #ifdef CONFIG_CRYPTO_FIPS
441 }, {
442 	.cra_name		= "fips(ansi_cprng)",
443 	.cra_driver_name	= "fips_ansi_cprng",
444 	.cra_priority		= 300,
445 	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
446 	.cra_ctxsize		= sizeof(struct prng_context),
447 	.cra_type		= &crypto_rng_type,
448 	.cra_module		= THIS_MODULE,
449 	.cra_init		= cprng_init,
450 	.cra_exit		= cprng_exit,
451 	.cra_u			= {
452 		.rng = {
453 			.rng_make_random	= fips_cprng_get_random,
454 			.rng_reset		= fips_cprng_reset,
455 			.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
456 		}
457 	}
458 #endif
459 } };
460 
461 /* Module initalization */
462 static int __init prng_mod_init(void)
463 {
464 	return crypto_register_algs(rng_algs, ARRAY_SIZE(rng_algs));
465 }
466 
467 static void __exit prng_mod_fini(void)
468 {
469 	crypto_unregister_algs(rng_algs, ARRAY_SIZE(rng_algs));
470 }
471 
472 MODULE_LICENSE("GPL");
473 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
474 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
475 module_param(dbg, int, 0);
476 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
477 module_init(prng_mod_init);
478 module_exit(prng_mod_fini);
479 MODULE_ALIAS("stdrng");
480