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Diffstat (limited to 'libc/bionic/arc4random.c')
| -rw-r--r-- | libc/bionic/arc4random.c | 308 |
1 files changed, 308 insertions, 0 deletions
diff --git a/libc/bionic/arc4random.c b/libc/bionic/arc4random.c new file mode 100644 index 0000000..d70580a --- /dev/null +++ b/libc/bionic/arc4random.c @@ -0,0 +1,308 @@ +/* $OpenBSD: arc4random.c,v 1.19 2008/06/04 00:50:23 djm Exp $ */ + +/* + * Copyright (c) 1996, David Mazieres <dm@uun.org> + * Copyright (c) 2008, Damien Miller <djm@openbsd.org> + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +/* + * Arc4 random number generator for OpenBSD. + * + * This code is derived from section 17.1 of Applied Cryptography, + * second edition, which describes a stream cipher allegedly + * compatible with RSA Labs "RC4" cipher (the actual description of + * which is a trade secret). The same algorithm is used as a stream + * cipher called "arcfour" in Tatu Ylonen's ssh package. + * + * Here the stream cipher has been modified always to include the time + * when initializing the state. That makes it impossible to + * regenerate the same random sequence twice, so this can't be used + * for encryption, but will generate good random numbers. + * + * RC4 is a registered trademark of RSA Laboratories. + */ + +#include <fcntl.h> +#include <limits.h> +#include <stdlib.h> +#include <unistd.h> +#include <sys/types.h> +#include <sys/param.h> +#include <sys/time.h> +#include "thread_private.h" + +/* BIONIC-BEGIN */ +/* this lock should protect the global variables in this file */ +static pthread_mutex_t _arc4_lock = PTHREAD_MUTEX_INITIALIZER; +#define _ARC4_LOCK() pthread_mutex_lock(&_arc4_lock) +#define _ARC4_UNLOCK() pthread_mutex_unlock(&_arc4_lock) +/* BIONIC-END */ + +#ifdef __GNUC__ +#define inline __inline +#else /* !__GNUC__ */ +#define inline +#endif /* !__GNUC__ */ + +struct arc4_stream { + u_int8_t i; + u_int8_t j; + u_int8_t s[256]; +}; + +static int rs_initialized; +static struct arc4_stream rs; +static pid_t arc4_stir_pid; +static int arc4_count; + +static inline u_int8_t arc4_getbyte(void); + +static inline void +arc4_init(void) +{ + int n; + + for (n = 0; n < 256; n++) + rs.s[n] = n; + rs.i = 0; + rs.j = 0; +} + +static inline void +arc4_addrandom(u_char *dat, int datlen) +{ + int n; + u_int8_t si; + + rs.i--; + for (n = 0; n < 256; n++) { + rs.i = (rs.i + 1); + si = rs.s[rs.i]; + rs.j = (rs.j + si + dat[n % datlen]); + rs.s[rs.i] = rs.s[rs.j]; + rs.s[rs.j] = si; + } + rs.j = rs.i; +} + +static void +arc4_stir(void) +{ +#if 1 /* BIONIC-BEGIN */ + int i, fd; + union { + struct timeval tv; + u_int rnd[128 / sizeof(u_int)]; + } rdat; + int n; + + if (!rs_initialized) { + arc4_init(); + rs_initialized = 1; + } + + fd = open("/dev/urandom", O_RDONLY); + if (fd != -1) { + read(fd, rdat.rnd, sizeof(rdat.rnd)); + close(fd); + } + else + { + /* fd < 0 ? Ah, what the heck. We'll just take + * whatever was on the stack. just add a little more + * time-based randomness though + */ + gettimeofday(&rdat.tv, NULL); + } + + arc4_stir_pid = getpid(); + arc4_addrandom((void *) &rdat, sizeof(rdat)); +#else /* BIONIC-END */ + int i, mib[2]; + size_t len; + u_char rnd[128]; + + if (!rs_initialized) { + arc4_init(); + rs_initialized = 1; + } + + mib[0] = CTL_KERN; + mib[1] = KERN_ARND; + + len = sizeof(rnd); + sysctl(mib, 2, rnd, &len, NULL, 0); + + arc4_stir_pid = getpid(); + arc4_addrandom(rnd, sizeof(rnd)); +#endif + /* + * Discard early keystream, as per recommendations in: + * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps + */ + for (i = 0; i < 256; i++) + (void)arc4_getbyte(); + arc4_count = 1600000; +} + +static inline u_int8_t +arc4_getbyte(void) +{ + u_int8_t si, sj; + + rs.i = (rs.i + 1); + si = rs.s[rs.i]; + rs.j = (rs.j + si); + sj = rs.s[rs.j]; + rs.s[rs.i] = sj; + rs.s[rs.j] = si; + return (rs.s[(si + sj) & 0xff]); +} + +u_int8_t +__arc4_getbyte(void) +{ + u_int8_t val; + + _ARC4_LOCK(); + if (--arc4_count == 0 || !rs_initialized) + arc4_stir(); + val = arc4_getbyte(); + _ARC4_UNLOCK(); + return val; +} + +static inline u_int32_t +arc4_getword(void) +{ + u_int32_t val; + val = arc4_getbyte() << 24; + val |= arc4_getbyte() << 16; + val |= arc4_getbyte() << 8; + val |= arc4_getbyte(); + return val; +} + +void +arc4random_stir(void) +{ + _ARC4_LOCK(); + arc4_stir(); + _ARC4_UNLOCK(); +} + +void +arc4random_addrandom(u_char *dat, int datlen) +{ + _ARC4_LOCK(); + if (!rs_initialized) + arc4_stir(); + arc4_addrandom(dat, datlen); + _ARC4_UNLOCK(); +} + +u_int32_t +arc4random(void) +{ + u_int32_t val; + _ARC4_LOCK(); + arc4_count -= 4; + if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != getpid()) + arc4_stir(); + val = arc4_getword(); + _ARC4_UNLOCK(); + return val; +} + +void +arc4random_buf(void *_buf, size_t n) +{ + u_char *buf = (u_char *)_buf; + _ARC4_LOCK(); + if (!rs_initialized || arc4_stir_pid != getpid()) + arc4_stir(); + while (n--) { + if (--arc4_count <= 0) + arc4_stir(); + buf[n] = arc4_getbyte(); + } + _ARC4_UNLOCK(); +} + +/* + * Calculate a uniformly distributed random number less than upper_bound + * avoiding "modulo bias". + * + * Uniformity is achieved by generating new random numbers until the one + * returned is outside the range [0, 2**32 % upper_bound). This + * guarantees the selected random number will be inside + * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) + * after reduction modulo upper_bound. + */ +u_int32_t +arc4random_uniform(u_int32_t upper_bound) +{ + u_int32_t r, min; + + if (upper_bound < 2) + return 0; + +#if (ULONG_MAX > 0xffffffffUL) + min = 0x100000000UL % upper_bound; +#else + /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ + if (upper_bound > 0x80000000) + min = 1 + ~upper_bound; /* 2**32 - upper_bound */ + else { + /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ + min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; + } +#endif + + /* + * This could theoretically loop forever but each retry has + * p > 0.5 (worst case, usually far better) of selecting a + * number inside the range we need, so it should rarely need + * to re-roll. + */ + for (;;) { + r = arc4random(); + if (r >= min) + break; + } + + return r % upper_bound; +} + +#if 0 +/*-------- Test code for i386 --------*/ +#include <stdio.h> +#include <machine/pctr.h> +int +main(int argc, char **argv) +{ + const int iter = 1000000; + int i; + pctrval v; + + v = rdtsc(); + for (i = 0; i < iter; i++) + arc4random(); + v = rdtsc() - v; + v /= iter; + + printf("%qd cycles\n", v); +} +#endif |