2 * PRNG: Pseudo Random Number Generator
3 * Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
6 * (C) Neil Horman <nhorman@tuxdriver.com>
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
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>
25 #define DEFAULT_PRNG_KEY "0123456789abcdef"
26 #define DEFAULT_PRNG_KSZ 16
27 #define DEFAULT_BLK_SZ 16
28 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
31 * Flags for the prng_context flags field
34 #define PRNG_FIXED_SIZE 0x1
35 #define PRNG_NEED_RESET 0x2
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
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];
54 struct crypto_cipher *tfm;
60 static void hexdump(char *note, unsigned char *buf, unsigned int len)
63 printk(KERN_CRIT "%s", note);
64 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
70 #define dbgprint(format, args...) do {\
72 printk(format, ##args);\
75 static void xor_vectors(unsigned char *in1, unsigned char *in2,
76 unsigned char *out, unsigned int size)
80 for (i = 0; i < size; i++)
81 out[i] = in1[i] ^ in2[i];
85 * Returns DEFAULT_BLK_SZ bytes of random data per call
86 * returns 0 if generation succeeded, <0 if something went wrong
88 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
91 unsigned char tmp[DEFAULT_BLK_SZ];
92 unsigned char *output = NULL;
95 dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
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);
103 * This algorithm is a 3 stage state machine
105 for (i = 0; i < 3; i++) {
110 * Start by encrypting the counter value
111 * This gives us an intermediate value I
113 memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
115 hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
120 * Next xor I with our secret vector V
121 * encrypt that result to obtain our
122 * pseudo random data which we output
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;
130 * First check that we didn't produce the same
131 * random data that we did last time around through this
133 if (!memcmp(ctx->rand_data, ctx->last_rand_data,
136 panic("cprng %p Failed repetition check!\n",
141 "ctx %p Failed repetition check!\n",
144 ctx->flags |= PRNG_NEED_RESET;
147 memcpy(ctx->last_rand_data, ctx->rand_data,
151 * Lastly xor the random data with I
152 * and encrypt that to obtain a new secret vector V
154 xor_vectors(ctx->rand_data, ctx->I, tmp,
157 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
162 /* do the encryption */
163 crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
168 * Now update our DT value
170 for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
176 dbgprint("Returning new block for context %p\n", ctx);
177 ctx->rand_data_valid = 0;
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);
187 /* Our exported functions */
188 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
191 unsigned char *ptr = buf;
192 unsigned int byte_count = (unsigned int)nbytes;
196 spin_lock_bh(&ctx->prng_lock);
199 if (ctx->flags & PRNG_NEED_RESET)
203 * If the FIXED_SIZE flag is on, only return whole blocks of
207 if (ctx->flags & PRNG_FIXED_SIZE) {
208 if (nbytes < DEFAULT_BLK_SZ)
210 byte_count = DEFAULT_BLK_SZ;
214 * Return 0 in case of success as mandated by the kernel
215 * crypto API interface definition.
219 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
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);
233 * Copy any data less than an entire block
235 if (byte_count < DEFAULT_BLK_SZ) {
237 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
238 *ptr = ctx->rand_data[ctx->rand_data_valid];
241 ctx->rand_data_valid++;
248 * Now copy whole blocks
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);
258 if (ctx->rand_data_valid > 0)
260 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
261 ctx->rand_data_valid += DEFAULT_BLK_SZ;
262 ptr += DEFAULT_BLK_SZ;
266 * Now go back and get any remaining partial block
272 spin_unlock_bh(&ctx->prng_lock);
273 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
278 static void free_prng_context(struct prng_context *ctx)
280 crypto_free_cipher(ctx->tfm);
283 static int reset_prng_context(struct prng_context *ctx,
284 unsigned char *key, size_t klen,
285 unsigned char *V, unsigned char *DT)
288 unsigned char *prng_key;
290 spin_lock_bh(&ctx->prng_lock);
291 ctx->flags |= PRNG_NEED_RESET;
293 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
296 klen = DEFAULT_PRNG_KSZ;
299 memcpy(ctx->V, V, DEFAULT_BLK_SZ);
301 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
304 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
306 memset(ctx->DT, 0, DEFAULT_BLK_SZ);
308 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
309 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
311 ctx->rand_data_valid = DEFAULT_BLK_SZ;
313 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
315 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
316 crypto_cipher_get_flags(ctx->tfm));
321 ctx->flags &= ~PRNG_NEED_RESET;
323 spin_unlock_bh(&ctx->prng_lock);
327 static int cprng_init(struct crypto_tfm *tfm)
329 struct prng_context *ctx = crypto_tfm_ctx(tfm);
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",
336 return PTR_ERR(ctx->tfm);
339 if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
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
347 ctx->flags |= PRNG_NEED_RESET;
351 static void cprng_exit(struct crypto_tfm *tfm)
353 free_prng_context(crypto_tfm_ctx(tfm));
356 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
359 struct prng_context *prng = crypto_rng_ctx(tfm);
361 return get_prng_bytes(rdata, dlen, prng, 0);
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
370 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
372 struct prng_context *prng = crypto_rng_ctx(tfm);
373 u8 *key = seed + DEFAULT_BLK_SZ;
376 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
379 if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
380 dt = key + DEFAULT_PRNG_KSZ;
382 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
384 if (prng->flags & PRNG_NEED_RESET)
389 #ifdef CONFIG_CRYPTO_FIPS
390 static int fips_cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
393 struct prng_context *prng = crypto_rng_ctx(tfm);
395 return get_prng_bytes(rdata, dlen, prng, 1);
398 static int fips_cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
400 u8 rdata[DEFAULT_BLK_SZ];
401 u8 *key = seed + DEFAULT_BLK_SZ;
404 struct prng_context *prng = crypto_rng_ctx(tfm);
406 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
409 /* fips strictly requires seed != key */
410 if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
413 rc = cprng_reset(tfm, seed, slen);
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;
427 static struct crypto_alg rng_algs[] = { {
428 .cra_name = "stdrng",
429 .cra_driver_name = "ansi_cprng",
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,
439 .rng_make_random = cprng_get_random,
440 .rng_reset = cprng_reset,
441 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
444 #ifdef CONFIG_CRYPTO_FIPS
446 .cra_name = "fips(ansi_cprng)",
447 .cra_driver_name = "fips_ansi_cprng",
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,
457 .rng_make_random = fips_cprng_get_random,
458 .rng_reset = fips_cprng_reset,
459 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
465 /* Module initalization */
466 static int __init prng_mod_init(void)
468 return crypto_register_algs(rng_algs, ARRAY_SIZE(rng_algs));
471 static void __exit prng_mod_fini(void)
473 crypto_unregister_algs(rng_algs, ARRAY_SIZE(rng_algs));
476 MODULE_LICENSE("GPL");
477 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
478 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
479 module_param(dbg, int, 0);
480 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
481 module_init(prng_mod_init);
482 module_exit(prng_mod_fini);
483 MODULE_ALIAS_CRYPTO("stdrng");
484 MODULE_ALIAS_CRYPTO("ansi_cprng");