xref: /openbmc/linux/crypto/ansi_cprng.c (revision dea54fba) 
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 #define DEFAULT_PRNG_KEY "0123456789abcdef"
24 #define DEFAULT_PRNG_KSZ 16
25 #define DEFAULT_BLK_SZ 16
26 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
27 
28 /*
29  * Flags for the prng_context flags field
30  */
31 
32 #define PRNG_FIXED_SIZE 0x1
33 #define PRNG_NEED_RESET 0x2
34 
35 /*
36  * Note: DT is our counter value
37  *	 I is our intermediate value
38  *	 V is our seed vector
39  * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
40  * for implementation details
41  */
42 
43 
44 struct prng_context {
45 	spinlock_t prng_lock;
46 	unsigned char rand_data[DEFAULT_BLK_SZ];
47 	unsigned char last_rand_data[DEFAULT_BLK_SZ];
48 	unsigned char DT[DEFAULT_BLK_SZ];
49 	unsigned char I[DEFAULT_BLK_SZ];
50 	unsigned char V[DEFAULT_BLK_SZ];
51 	u32 rand_data_valid;
52 	struct crypto_cipher *tfm;
53 	u32 flags;
54 };
55 
56 static int dbg;
57 
58 static void hexdump(char *note, unsigned char *buf, unsigned int len)
59 {
60 	if (dbg) {
61 		printk(KERN_CRIT "%s", note);
62 		print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
63 				16, 1,
64 				buf, len, false);
65 	}
66 }
67 
68 #define dbgprint(format, args...) do {\
69 if (dbg)\
70 	printk(format, ##args);\
71 } while (0)
72 
73 static void xor_vectors(unsigned char *in1, unsigned char *in2,
74 			unsigned char *out, unsigned int size)
75 {
76 	int i;
77 
78 	for (i = 0; i < size; i++)
79 		out[i] = in1[i] ^ in2[i];
80 
81 }
82 /*
83  * Returns DEFAULT_BLK_SZ bytes of random data per call
84  * returns 0 if generation succeeded, <0 if something went wrong
85  */
86 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
87 {
88 	int i;
89 	unsigned char tmp[DEFAULT_BLK_SZ];
90 	unsigned char *output = NULL;
91 
92 
93 	dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
94 		ctx);
95 
96 	hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
97 	hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
98 	hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
99 
100 	/*
101 	 * This algorithm is a 3 stage state machine
102 	 */
103 	for (i = 0; i < 3; i++) {
104 
105 		switch (i) {
106 		case 0:
107 			/*
108 			 * Start by encrypting the counter value
109 			 * This gives us an intermediate value I
110 			 */
111 			memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
112 			output = ctx->I;
113 			hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
114 			break;
115 		case 1:
116 
117 			/*
118 			 * Next xor I with our secret vector V
119 			 * encrypt that result to obtain our
120 			 * pseudo random data which we output
121 			 */
122 			xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
123 			hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
124 			output = ctx->rand_data;
125 			break;
126 		case 2:
127 			/*
128 			 * First check that we didn't produce the same
129 			 * random data that we did last time around through this
130 			 */
131 			if (!memcmp(ctx->rand_data, ctx->last_rand_data,
132 					DEFAULT_BLK_SZ)) {
133 				if (cont_test) {
134 					panic("cprng %p Failed repetition check!\n",
135 						ctx);
136 				}
137 
138 				printk(KERN_ERR
139 					"ctx %p Failed repetition check!\n",
140 					ctx);
141 
142 				ctx->flags |= PRNG_NEED_RESET;
143 				return -EINVAL;
144 			}
145 			memcpy(ctx->last_rand_data, ctx->rand_data,
146 				DEFAULT_BLK_SZ);
147 
148 			/*
149 			 * Lastly xor the random data with I
150 			 * and encrypt that to obtain a new secret vector V
151 			 */
152 			xor_vectors(ctx->rand_data, ctx->I, tmp,
153 				DEFAULT_BLK_SZ);
154 			output = ctx->V;
155 			hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
156 			break;
157 		}
158 
159 
160 		/* do the encryption */
161 		crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
162 
163 	}
164 
165 	/*
166 	 * Now update our DT value
167 	 */
168 	for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
169 		ctx->DT[i] += 1;
170 		if (ctx->DT[i] != 0)
171 			break;
172 	}
173 
174 	dbgprint("Returning new block for context %p\n", ctx);
175 	ctx->rand_data_valid = 0;
176 
177 	hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
178 	hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
179 	hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
180 	hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
181 
182 	return 0;
183 }
184 
185 /* Our exported functions */
186 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
187 				int do_cont_test)
188 {
189 	unsigned char *ptr = buf;
190 	unsigned int byte_count = (unsigned int)nbytes;
191 	int err;
192 
193 
194 	spin_lock_bh(&ctx->prng_lock);
195 
196 	err = -EINVAL;
197 	if (ctx->flags & PRNG_NEED_RESET)
198 		goto done;
199 
200 	/*
201 	 * If the FIXED_SIZE flag is on, only return whole blocks of
202 	 * pseudo random data
203 	 */
204 	err = -EINVAL;
205 	if (ctx->flags & PRNG_FIXED_SIZE) {
206 		if (nbytes < DEFAULT_BLK_SZ)
207 			goto done;
208 		byte_count = DEFAULT_BLK_SZ;
209 	}
210 
211 	/*
212 	 * Return 0 in case of success as mandated by the kernel
213 	 * crypto API interface definition.
214 	 */
215 	err = 0;
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, do_cont_test) < 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 		while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
236 			*ptr = ctx->rand_data[ctx->rand_data_valid];
237 			ptr++;
238 			byte_count--;
239 			ctx->rand_data_valid++;
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, do_cont_test) < 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 			      const unsigned char *key, size_t klen,
283 			      const unsigned char *V, const unsigned char *DT)
284 {
285 	int ret;
286 	const 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,
355 			    const u8 *src, unsigned int slen,
356 			    u8 *rdata, unsigned int dlen)
357 {
358 	struct prng_context *prng = crypto_rng_ctx(tfm);
359 
360 	return get_prng_bytes(rdata, dlen, prng, 0);
361 }
362 
363 /*
364  *  This is the cprng_registered reset method the seed value is
365  *  interpreted as the tuple { V KEY DT}
366  *  V and KEY are required during reset, and DT is optional, detected
367  *  as being present by testing the length of the seed
368  */
369 static int cprng_reset(struct crypto_rng *tfm,
370 		       const u8 *seed, unsigned int slen)
371 {
372 	struct prng_context *prng = crypto_rng_ctx(tfm);
373 	const u8 *key = seed + DEFAULT_BLK_SZ;
374 	const 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,
391 				 const u8 *src, unsigned int slen,
392 				 u8 *rdata, unsigned int dlen)
393 {
394 	struct prng_context *prng = crypto_rng_ctx(tfm);
395 
396 	return get_prng_bytes(rdata, dlen, prng, 1);
397 }
398 
399 static int fips_cprng_reset(struct crypto_rng *tfm,
400 			    const u8 *seed, unsigned int slen)
401 {
402 	u8 rdata[DEFAULT_BLK_SZ];
403 	const u8 *key = seed + DEFAULT_BLK_SZ;
404 	int rc;
405 
406 	struct prng_context *prng = crypto_rng_ctx(tfm);
407 
408 	if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
409 		return -EINVAL;
410 
411 	/* fips strictly requires seed != key */
412 	if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
413 		return -EINVAL;
414 
415 	rc = cprng_reset(tfm, seed, slen);
416 
417 	if (!rc)
418 		goto out;
419 
420 	/* this primes our continuity test */
421 	rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
422 	prng->rand_data_valid = DEFAULT_BLK_SZ;
423 
424 out:
425 	return rc;
426 }
427 #endif
428 
429 static struct rng_alg rng_algs[] = { {
430 	.generate		= cprng_get_random,
431 	.seed			= cprng_reset,
432 	.seedsize		= DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
433 	.base			=	{
434 		.cra_name		= "stdrng",
435 		.cra_driver_name	= "ansi_cprng",
436 		.cra_priority		= 100,
437 		.cra_ctxsize		= sizeof(struct prng_context),
438 		.cra_module		= THIS_MODULE,
439 		.cra_init		= cprng_init,
440 		.cra_exit		= cprng_exit,
441 	}
442 #ifdef CONFIG_CRYPTO_FIPS
443 }, {
444 	.generate		= fips_cprng_get_random,
445 	.seed			= fips_cprng_reset,
446 	.seedsize		= DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
447 	.base			=	{
448 		.cra_name		= "fips(ansi_cprng)",
449 		.cra_driver_name	= "fips_ansi_cprng",
450 		.cra_priority		= 300,
451 		.cra_ctxsize		= sizeof(struct prng_context),
452 		.cra_module		= THIS_MODULE,
453 		.cra_init		= cprng_init,
454 		.cra_exit		= cprng_exit,
455 	}
456 #endif
457 } };
458 
459 /* Module initalization */
460 static int __init prng_mod_init(void)
461 {
462 	return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
463 }
464 
465 static void __exit prng_mod_fini(void)
466 {
467 	crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
468 }
469 
470 MODULE_LICENSE("GPL");
471 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
472 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
473 module_param(dbg, int, 0);
474 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
475 module_init(prng_mod_init);
476 module_exit(prng_mod_fini);
477 MODULE_ALIAS_CRYPTO("stdrng");
478 MODULE_ALIAS_CRYPTO("ansi_cprng");
479