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
46struct 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
58static int dbg;
59
60static 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 {\
71if (dbg)\
72	printk(format, ##args);\
73} while (0)
74
75static 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 */
88static 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 */
188static 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
219remainder:
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) {
232empty_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
267done:
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
274static void free_prng_context(struct prng_context *ctx)
275{
276	crypto_free_cipher(ctx->tfm);
277}
278
279static 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;
318out:
319	spin_unlock_bh(&ctx->prng_lock);
320	return ret;
321}
322
323static 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
347static void cprng_exit(struct crypto_tfm *tfm)
348{
349	free_prng_context(crypto_tfm_ctx(tfm));
350}
351
352static 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 */
366static 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
385static struct crypto_alg rng_alg = {
386	.cra_name		= "stdrng",
387	.cra_driver_name	= "ansi_cprng",
388	.cra_priority		= 100,
389	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
390	.cra_ctxsize		= sizeof(struct prng_context),
391	.cra_type		= &crypto_rng_type,
392	.cra_module		= THIS_MODULE,
393	.cra_list		= LIST_HEAD_INIT(rng_alg.cra_list),
394	.cra_init		= cprng_init,
395	.cra_exit		= cprng_exit,
396	.cra_u			= {
397		.rng = {
398			.rng_make_random	= cprng_get_random,
399			.rng_reset		= cprng_reset,
400			.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
401		}
402	}
403};
404
405#ifdef CONFIG_CRYPTO_FIPS
406static int fips_cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
407			    unsigned int dlen)
408{
409	struct prng_context *prng = crypto_rng_ctx(tfm);
410
411	return get_prng_bytes(rdata, dlen, prng, 1);
412}
413
414static int fips_cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
415{
416	u8 rdata[DEFAULT_BLK_SZ];
417	int rc;
418
419	struct prng_context *prng = crypto_rng_ctx(tfm);
420
421	rc = cprng_reset(tfm, seed, slen);
422
423	if (!rc)
424		goto out;
425
426	/* this primes our continuity test */
427	rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
428	prng->rand_data_valid = DEFAULT_BLK_SZ;
429
430out:
431	return rc;
432}
433
434static struct crypto_alg fips_rng_alg = {
435	.cra_name		= "fips(ansi_cprng)",
436	.cra_driver_name	= "fips_ansi_cprng",
437	.cra_priority		= 300,
438	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
439	.cra_ctxsize		= sizeof(struct prng_context),
440	.cra_type		= &crypto_rng_type,
441	.cra_module		= THIS_MODULE,
442	.cra_list		= LIST_HEAD_INIT(rng_alg.cra_list),
443	.cra_init		= cprng_init,
444	.cra_exit		= cprng_exit,
445	.cra_u			= {
446		.rng = {
447			.rng_make_random	= fips_cprng_get_random,
448			.rng_reset		= fips_cprng_reset,
449			.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
450		}
451	}
452};
453#endif
454
455/* Module initalization */
456static int __init prng_mod_init(void)
457{
458	int rc = 0;
459
460	rc = crypto_register_alg(&rng_alg);
461#ifdef CONFIG_CRYPTO_FIPS
462	if (rc)
463		goto out;
464
465	rc = crypto_register_alg(&fips_rng_alg);
466
467out:
468#endif
469	return rc;
470}
471
472static void __exit prng_mod_fini(void)
473{
474	crypto_unregister_alg(&rng_alg);
475#ifdef CONFIG_CRYPTO_FIPS
476	crypto_unregister_alg(&fips_rng_alg);
477#endif
478	return;
479}
480
481MODULE_LICENSE("GPL");
482MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
483MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
484module_param(dbg, int, 0);
485MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
486module_init(prng_mod_init);
487module_exit(prng_mod_fini);
488MODULE_ALIAS("stdrng");
489