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 succeded, <0 if something went wrong
87 */
88static int _get_more_prng_bytes(struct prng_context *ctx)
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 (fips_enabled) {
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{
190    unsigned char *ptr = buf;
191    unsigned int byte_count = (unsigned int)nbytes;
192    int err;
193
194
195    if (nbytes < 0)
196        return -EINVAL;
197
198    spin_lock_bh(&ctx->prng_lock);
199
200    err = -EINVAL;
201    if (ctx->flags & PRNG_NEED_RESET)
202        goto done;
203
204    /*
205     * If the FIXED_SIZE flag is on, only return whole blocks of
206     * pseudo random data
207     */
208    err = -EINVAL;
209    if (ctx->flags & PRNG_FIXED_SIZE) {
210        if (nbytes < DEFAULT_BLK_SZ)
211            goto done;
212        byte_count = DEFAULT_BLK_SZ;
213    }
214
215    err = byte_count;
216
217    dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
218        byte_count, ctx);
219
220
221remainder:
222    if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
223        if (_get_more_prng_bytes(ctx) < 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) {
234empty_rbuf:
235        for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
236            ctx->rand_data_valid++) {
237            *ptr = ctx->rand_data[ctx->rand_data_valid];
238            ptr++;
239            byte_count--;
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) < 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
269done:
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
276static void free_prng_context(struct prng_context *ctx)
277{
278    crypto_free_cipher(ctx->tfm);
279}
280
281static int reset_prng_context(struct prng_context *ctx,
282                  unsigned char *key, size_t klen,
283                  unsigned char *V, unsigned char *DT)
284{
285    int ret;
286    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;
320out:
321    spin_unlock_bh(&ctx->prng_lock);
322    return ret;
323}
324
325static 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
349static void cprng_exit(struct crypto_tfm *tfm)
350{
351    free_prng_context(crypto_tfm_ctx(tfm));
352}
353
354static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
355                unsigned int dlen)
356{
357    struct prng_context *prng = crypto_rng_ctx(tfm);
358
359    return get_prng_bytes(rdata, dlen, prng);
360}
361
362/*
363 * This is the cprng_registered reset method the seed value is
364 * interpreted as the tuple { V KEY DT}
365 * V and KEY are required during reset, and DT is optional, detected
366 * as being present by testing the length of the seed
367 */
368static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
369{
370    struct prng_context *prng = crypto_rng_ctx(tfm);
371    u8 *key = seed + DEFAULT_BLK_SZ;
372    u8 *dt = NULL;
373
374    if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
375        return -EINVAL;
376
377    if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
378        dt = key + DEFAULT_PRNG_KSZ;
379
380    reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
381
382    if (prng->flags & PRNG_NEED_RESET)
383        return -EINVAL;
384    return 0;
385}
386
387static struct crypto_alg rng_alg = {
388    .cra_name = "stdrng",
389    .cra_driver_name = "ansi_cprng",
390    .cra_priority = 100,
391    .cra_flags = CRYPTO_ALG_TYPE_RNG,
392    .cra_ctxsize = sizeof(struct prng_context),
393    .cra_type = &crypto_rng_type,
394    .cra_module = THIS_MODULE,
395    .cra_list = LIST_HEAD_INIT(rng_alg.cra_list),
396    .cra_init = cprng_init,
397    .cra_exit = cprng_exit,
398    .cra_u = {
399        .rng = {
400            .rng_make_random = cprng_get_random,
401            .rng_reset = cprng_reset,
402            .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
403        }
404    }
405};
406
407
408/* Module initalization */
409static int __init prng_mod_init(void)
410{
411    if (fips_enabled)
412        rng_alg.cra_priority += 200;
413
414    return crypto_register_alg(&rng_alg);
415}
416
417static void __exit prng_mod_fini(void)
418{
419    crypto_unregister_alg(&rng_alg);
420    return;
421}
422
423MODULE_LICENSE("GPL");
424MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
425MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
426module_param(dbg, int, 0);
427MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
428module_init(prng_mod_init);
429module_exit(prng_mod_fini);
430MODULE_ALIAS("stdrng");
431

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