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 succeeded, <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	/*
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
223remainder:
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) {
236empty_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
271done:
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
278static void free_prng_context(struct prng_context *ctx)
279{
280	crypto_free_cipher(ctx->tfm);
281}
282
283static 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;
322out:
323	spin_unlock_bh(&ctx->prng_lock);
324	return ret;
325}
326
327static 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
351static void cprng_exit(struct crypto_tfm *tfm)
352{
353	free_prng_context(crypto_tfm_ctx(tfm));
354}
355
356static 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 */
370static 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
390static 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
398static 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
422out:
423	return rc;
424}
425#endif
426
427static 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 */
466static int __init prng_mod_init(void)
467{
468	return crypto_register_algs(rng_algs, ARRAY_SIZE(rng_algs));
469}
470
471static void __exit prng_mod_fini(void)
472{
473	crypto_unregister_algs(rng_algs, ARRAY_SIZE(rng_algs));
474}
475
476MODULE_LICENSE("GPL");
477MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
478MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
479module_param(dbg, int, 0);
480MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
481module_init(prng_mod_init);
482module_exit(prng_mod_fini);
483MODULE_ALIAS_CRYPTO("stdrng");
484MODULE_ALIAS_CRYPTO("ansi_cprng");
485