xref: /openbmc/linux/crypto/ansi_cprng.c (revision 94cdda6b) 
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 	/*
214 	 * Return 0 in case of success as mandated by the kernel
215 	 * crypto API interface definition.
216 	 */
217 	err = 0;
218 
219 	dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
220 		byte_count, ctx);
221 
222 
223 remainder:
224 	if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
225 		if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
226 			memset(buf, 0, nbytes);
227 			err = -EINVAL;
228 			goto done;
229 		}
230 	}
231 
232 	/*
233 	 * Copy any data less than an entire block
234 	 */
235 	if (byte_count < DEFAULT_BLK_SZ) {
236 empty_rbuf:
237 		while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
238 			*ptr = ctx->rand_data[ctx->rand_data_valid];
239 			ptr++;
240 			byte_count--;
241 			ctx->rand_data_valid++;
242 			if (byte_count == 0)
243 				goto done;
244 		}
245 	}
246 
247 	/*
248 	 * Now copy whole blocks
249 	 */
250 	for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
251 		if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
252 			if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
253 				memset(buf, 0, nbytes);
254 				err = -EINVAL;
255 				goto done;
256 			}
257 		}
258 		if (ctx->rand_data_valid > 0)
259 			goto empty_rbuf;
260 		memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
261 		ctx->rand_data_valid += DEFAULT_BLK_SZ;
262 		ptr += DEFAULT_BLK_SZ;
263 	}
264 
265 	/*
266 	 * Now go back and get any remaining partial block
267 	 */
268 	if (byte_count)
269 		goto remainder;
270 
271 done:
272 	spin_unlock_bh(&ctx->prng_lock);
273 	dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
274 		err, ctx);
275 	return err;
276 }
277 
278 static void free_prng_context(struct prng_context *ctx)
279 {
280 	crypto_free_cipher(ctx->tfm);
281 }
282 
283 static int reset_prng_context(struct prng_context *ctx,
284 			      unsigned char *key, size_t klen,
285 			      unsigned char *V, unsigned char *DT)
286 {
287 	int ret;
288 	unsigned char *prng_key;
289 
290 	spin_lock_bh(&ctx->prng_lock);
291 	ctx->flags |= PRNG_NEED_RESET;
292 
293 	prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
294 
295 	if (!key)
296 		klen = DEFAULT_PRNG_KSZ;
297 
298 	if (V)
299 		memcpy(ctx->V, V, DEFAULT_BLK_SZ);
300 	else
301 		memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
302 
303 	if (DT)
304 		memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
305 	else
306 		memset(ctx->DT, 0, DEFAULT_BLK_SZ);
307 
308 	memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
309 	memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
310 
311 	ctx->rand_data_valid = DEFAULT_BLK_SZ;
312 
313 	ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
314 	if (ret) {
315 		dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
316 			crypto_cipher_get_flags(ctx->tfm));
317 		goto out;
318 	}
319 
320 	ret = 0;
321 	ctx->flags &= ~PRNG_NEED_RESET;
322 out:
323 	spin_unlock_bh(&ctx->prng_lock);
324 	return ret;
325 }
326 
327 static int cprng_init(struct crypto_tfm *tfm)
328 {
329 	struct prng_context *ctx = crypto_tfm_ctx(tfm);
330 
331 	spin_lock_init(&ctx->prng_lock);
332 	ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
333 	if (IS_ERR(ctx->tfm)) {
334 		dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
335 				ctx);
336 		return PTR_ERR(ctx->tfm);
337 	}
338 
339 	if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
340 		return -EINVAL;
341 
342 	/*
343 	 * after allocation, we should always force the user to reset
344 	 * so they don't inadvertently use the insecure default values
345 	 * without specifying them intentially
346 	 */
347 	ctx->flags |= PRNG_NEED_RESET;
348 	return 0;
349 }
350 
351 static void cprng_exit(struct crypto_tfm *tfm)
352 {
353 	free_prng_context(crypto_tfm_ctx(tfm));
354 }
355 
356 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
357 			    unsigned int dlen)
358 {
359 	struct prng_context *prng = crypto_rng_ctx(tfm);
360 
361 	return get_prng_bytes(rdata, dlen, prng, 0);
362 }
363 
364 /*
365  *  This is the cprng_registered reset method the seed value is
366  *  interpreted as the tuple { V KEY DT}
367  *  V and KEY are required during reset, and DT is optional, detected
368  *  as being present by testing the length of the seed
369  */
370 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
371 {
372 	struct prng_context *prng = crypto_rng_ctx(tfm);
373 	u8 *key = seed + DEFAULT_BLK_SZ;
374 	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, u8 *rdata,
391 			    unsigned int dlen)
392 {
393 	struct prng_context *prng = crypto_rng_ctx(tfm);
394 
395 	return get_prng_bytes(rdata, dlen, prng, 1);
396 }
397 
398 static int fips_cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
399 {
400 	u8 rdata[DEFAULT_BLK_SZ];
401 	u8 *key = seed + DEFAULT_BLK_SZ;
402 	int rc;
403 
404 	struct prng_context *prng = crypto_rng_ctx(tfm);
405 
406 	if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
407 		return -EINVAL;
408 
409 	/* fips strictly requires seed != key */
410 	if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
411 		return -EINVAL;
412 
413 	rc = cprng_reset(tfm, seed, slen);
414 
415 	if (!rc)
416 		goto out;
417 
418 	/* this primes our continuity test */
419 	rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
420 	prng->rand_data_valid = DEFAULT_BLK_SZ;
421 
422 out:
423 	return rc;
424 }
425 #endif
426 
427 static struct crypto_alg rng_algs[] = { {
428 	.cra_name		= "stdrng",
429 	.cra_driver_name	= "ansi_cprng",
430 	.cra_priority		= 100,
431 	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
432 	.cra_ctxsize		= sizeof(struct prng_context),
433 	.cra_type		= &crypto_rng_type,
434 	.cra_module		= THIS_MODULE,
435 	.cra_init		= cprng_init,
436 	.cra_exit		= cprng_exit,
437 	.cra_u			= {
438 		.rng = {
439 			.rng_make_random	= cprng_get_random,
440 			.rng_reset		= cprng_reset,
441 			.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
442 		}
443 	}
444 #ifdef CONFIG_CRYPTO_FIPS
445 }, {
446 	.cra_name		= "fips(ansi_cprng)",
447 	.cra_driver_name	= "fips_ansi_cprng",
448 	.cra_priority		= 300,
449 	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
450 	.cra_ctxsize		= sizeof(struct prng_context),
451 	.cra_type		= &crypto_rng_type,
452 	.cra_module		= THIS_MODULE,
453 	.cra_init		= cprng_init,
454 	.cra_exit		= cprng_exit,
455 	.cra_u			= {
456 		.rng = {
457 			.rng_make_random	= fips_cprng_get_random,
458 			.rng_reset		= fips_cprng_reset,
459 			.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
460 		}
461 	}
462 #endif
463 } };
464 
465 /* Module initalization */
466 static int __init prng_mod_init(void)
467 {
468 	return crypto_register_algs(rng_algs, ARRAY_SIZE(rng_algs));
469 }
470 
471 static void __exit prng_mod_fini(void)
472 {
473 	crypto_unregister_algs(rng_algs, ARRAY_SIZE(rng_algs));
474 }
475 
476 MODULE_LICENSE("GPL");
477 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
478 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
479 module_param(dbg, int, 0);
480 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
481 module_init(prng_mod_init);
482 module_exit(prng_mod_fini);
483 MODULE_ALIAS_CRYPTO("stdrng");
484 MODULE_ALIAS_CRYPTO("ansi_cprng");
485