ash,hush: improve randomness of $RANDOM, add easy-ish way to test it
function old new delta next_random 68 113 +45 change_random 103 121 +18 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
parent
69f9567de2
commit
fb183076a3
136
shell/random.c
136
shell/random.c
@ -6,17 +6,51 @@
|
||||
*
|
||||
* Licensed under GPLv2, see file LICENSE in this source tree.
|
||||
*/
|
||||
#include "libbb.h"
|
||||
#include "random.h"
|
||||
|
||||
/* For testing against dieharder, you need only random.{c,h}
|
||||
* Howto:
|
||||
* gcc -O2 -Wall -DRANDTEST random.c -o random
|
||||
* ./random | dieharder -g 200 -a
|
||||
*/
|
||||
|
||||
#if !defined RANDTEST
|
||||
|
||||
# include "libbb.h"
|
||||
# include "random.h"
|
||||
# define RAND_BASH_MASK 0x7fff
|
||||
|
||||
#else
|
||||
# include <stdint.h>
|
||||
# include <unistd.h>
|
||||
# include <stdio.h>
|
||||
# include <time.h>
|
||||
# define RAND_BASH_MASK 0xffffffff /* off */
|
||||
# define FAST_FUNC /* nothing */
|
||||
# define PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN /* nothing */
|
||||
# define POP_SAVED_FUNCTION_VISIBILITY /* nothing */
|
||||
# define monotonic_us() time(NULL)
|
||||
# include "random.h"
|
||||
#endif
|
||||
|
||||
uint32_t FAST_FUNC
|
||||
next_random(random_t *rnd)
|
||||
{
|
||||
/* Galois LFSR parameter */
|
||||
/* Taps at 32 31 29 1: */
|
||||
/* Galois LFSR parameter:
|
||||
* Taps at 32 31 29 1:
|
||||
*/
|
||||
enum { MASK = 0x8000000b };
|
||||
/* Another example - taps at 32 31 30 10: */
|
||||
/* MASK = 0x00400007 */
|
||||
/* enum { MASK = 0x00400007 }; */
|
||||
|
||||
/* Xorshift parameters:
|
||||
* Choices for a,b,c: 10,13,10; 8,9,22; 2,7,3; 23,3,24
|
||||
* (given by algorithm author)
|
||||
*/
|
||||
enum {
|
||||
a = 2,
|
||||
b = 7,
|
||||
c = 3,
|
||||
};
|
||||
|
||||
uint32_t t;
|
||||
|
||||
@ -27,18 +61,94 @@ next_random(random_t *rnd)
|
||||
INIT_RANDOM_T(rnd, getpid(), monotonic_us());
|
||||
}
|
||||
|
||||
/* LCG has period of 2^32 and alternating lowest bit */
|
||||
/* LCG: period of 2^32, but quite weak:
|
||||
* bit 0 alternates beetween 0 and 1 (pattern of length 2)
|
||||
* bit 1 has a repeating pattern of length 4
|
||||
* bit 2 has a repeating pattern of length 8
|
||||
* etc...
|
||||
*/
|
||||
rnd->LCG = 1664525 * rnd->LCG + 1013904223;
|
||||
/* Galois LFSR has period of 2^32-1 = 3 * 5 * 17 * 257 * 65537 */
|
||||
|
||||
/* Galois LFSR:
|
||||
* period of 2^32-1 = 3 * 5 * 17 * 257 * 65537.
|
||||
* Successive values are right-shifted one bit
|
||||
* and possibly xored with a sparse constant.
|
||||
*/
|
||||
t = (rnd->galois_LFSR << 1);
|
||||
if (rnd->galois_LFSR < 0) /* if we just shifted 1 out of msb... */
|
||||
t ^= MASK;
|
||||
rnd->galois_LFSR = t;
|
||||
/* Both are weak, combining them gives better randomness
|
||||
* and ~2^64 period. & 0x7fff is probably bash compat
|
||||
* for $RANDOM range. Combining with subtraction is
|
||||
* just for fun. + and ^ would work equally well. */
|
||||
t = (t - rnd->LCG) & 0x7fff;
|
||||
|
||||
return t;
|
||||
/* http://en.wikipedia.org/wiki/Xorshift
|
||||
* Period 2^64-1 = 3 * 715827883 * 2147483647
|
||||
* Moderately good statistical properties:
|
||||
* fails the following "dieharder -g 200 -a" tests:
|
||||
* diehard_operm5| 0
|
||||
* diehard_oqso| 0
|
||||
* diehard_count_1s_byt| 0
|
||||
* diehard_3dsphere| 3
|
||||
* diehard_squeeze| 0
|
||||
* diehard_runs| 0
|
||||
* diehard_runs| 0
|
||||
* diehard_craps| 0
|
||||
* diehard_craps| 0
|
||||
* rgb_minimum_distance| 3
|
||||
* rgb_minimum_distance| 4
|
||||
* rgb_minimum_distance| 5
|
||||
* rgb_permutations| 3
|
||||
* rgb_permutations| 4
|
||||
* rgb_permutations| 5
|
||||
* dab_filltree| 32
|
||||
* dab_filltree| 32
|
||||
* dab_monobit2| 12
|
||||
*/
|
||||
t = rnd->xs64_x ^ (rnd->xs64_x << a);
|
||||
rnd->xs64_x = rnd->xs64_y;
|
||||
rnd->xs64_y = rnd->xs64_y ^ (rnd->xs64_y >> c) ^ t ^ (t >> b);
|
||||
|
||||
/* Combined LCG + Galois LFSR have 2^32 * 2^32-1 period.
|
||||
* Strength:
|
||||
* individually, both are extremely weak cryptographycally;
|
||||
* when combined, they fail the following "dieharder -g 200 -a" tests:
|
||||
* diehard_rank_6x8| 0
|
||||
* diehard_oqso| 0
|
||||
* diehard_dna| 0
|
||||
* diehard_count_1s_byt| 0
|
||||
* rgb_bitdist| 2
|
||||
* dab_monobit2| 12
|
||||
*
|
||||
* Combining them with xorshift-64 increases period to
|
||||
* 2^32 * 2^32-1 * 2^64-1 / 3
|
||||
* (2^32-1 and 2^64-1 have one common divisor 3, hence "/ 3" part),
|
||||
* which is about 2^128 / 3, or in base 10 ~1.13*10^38.
|
||||
* Strength of the combination:
|
||||
* passes all "dieharder -g 200 -a" tests.
|
||||
*
|
||||
* Combining with subtraction and addition is just for fun.
|
||||
* It does not add meaningful strength, could use xor operation instead.
|
||||
*/
|
||||
t = rnd->galois_LFSR - rnd->LCG + rnd->xs64_y;
|
||||
|
||||
/* bash compat $RANDOM range: */
|
||||
return t & RAND_BASH_MASK;
|
||||
}
|
||||
|
||||
#ifdef RANDTEST
|
||||
static random_t rnd;
|
||||
|
||||
int main(int argc, char **argv)
|
||||
{
|
||||
int i;
|
||||
int buf[4096];
|
||||
|
||||
for (;;) {
|
||||
for (i = 0; i < sizeof(buf) / sizeof(buf[0]); i++) {
|
||||
buf[i] = next_random(&rnd);
|
||||
}
|
||||
write(1, buf, sizeof(buf));
|
||||
}
|
||||
|
||||
return 0;
|
||||
}
|
||||
|
||||
#endif
|
||||
|
||||
@ -12,16 +12,24 @@
|
||||
PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN
|
||||
|
||||
typedef struct random_t {
|
||||
/* Random number generators */
|
||||
int32_t galois_LFSR; /* Galois LFSR (fast but weak). signed! */
|
||||
uint32_t LCG; /* LCG (fast but weak) */
|
||||
/* State of random number generators: */
|
||||
|
||||
/* Galois LFSR (fast but weak) */
|
||||
int32_t galois_LFSR; /* must be signed! */
|
||||
|
||||
/* LCG (fast but weak) */
|
||||
uint32_t LCG;
|
||||
|
||||
/* 64-bit xorshift (fast, moderate strength) */
|
||||
uint32_t xs64_x;
|
||||
uint32_t xs64_y;
|
||||
} random_t;
|
||||
|
||||
#define UNINITED_RANDOM_T(rnd) \
|
||||
((rnd)->galois_LFSR == 0)
|
||||
|
||||
#define INIT_RANDOM_T(rnd, nonzero, v) \
|
||||
((rnd)->galois_LFSR = (nonzero), (rnd)->LCG = (v))
|
||||
((rnd)->galois_LFSR = (rnd)->xs64_x = (nonzero), (rnd)->LCG = (rnd)->xs64_y = (v))
|
||||
|
||||
#define CLEAR_RANDOM_T(rnd) \
|
||||
((rnd)->galois_LFSR = 0)
|
||||
|
||||
Loading…
Reference in New Issue
Block a user