Root/crypto/ansi_cprng.c

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    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        while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
234            *ptr = ctx->rand_data[ctx->rand_data_valid];
235            ptr++;
236            byte_count--;
237            ctx->rand_data_valid++;
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
385#ifdef CONFIG_CRYPTO_FIPS
386static 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
394static 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
418out:
419    return rc;
420}
421#endif
422
423static 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 */
462static int __init prng_mod_init(void)
463{
464    return crypto_register_algs(rng_algs, ARRAY_SIZE(rng_algs));
465}
466
467static void __exit prng_mod_fini(void)
468{
469    crypto_unregister_algs(rng_algs, ARRAY_SIZE(rng_algs));
470}
471
472MODULE_LICENSE("GPL");
473MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
474MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
475module_param(dbg, int, 0);
476MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
477module_init(prng_mod_init);
478module_exit(prng_mod_fini);
479MODULE_ALIAS("stdrng");
480

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