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Add an arc4random implementation for use by evdns
Previously, evdns was at the mercy of the user for providing a good entropy source; without one, it would be vulnerable to various active attacks. This patch adds a port of OpenBSD's arc4random() calls to Libevent [port by Chris Davis], and wraps it up a little bit so we can use it more safely.
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/* Portable arc4random.c based on arc4random.c from OpenBSD. | ||
* Portable version by Chris Davis, adapted for Libevent by Nick Mathewson | ||
* | ||
* Note that in Libevent, this file isn't compiled directly. Instead, | ||
* it's included from evutil_rand.c | ||
*/ | ||
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/* | ||
* 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. | ||
*/ | ||
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/* | ||
* 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. | ||
*/ | ||
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#ifndef ARC4RANDOM_EXPORT | ||
#define ARC4RANDOM_EXPORT | ||
#endif | ||
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#ifndef ARC4RANDOM_NO_INCLUDES | ||
#ifdef WIN32 | ||
#include <wincrypt.h> | ||
#else | ||
#include <fcntl.h> | ||
#include <unistd.h> | ||
#include <sys/param.h> | ||
#include <sys/time.h> | ||
#endif | ||
#include <limits.h> | ||
#include <stdlib.h> | ||
#include <string.h> | ||
#endif | ||
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/* Add platform entropy 32 bytes (256 bits) at a time. */ | ||
#define ADD_ENTROPY 32 | ||
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/* Re-seed from the platform RNG after generating this many bytes. */ | ||
#define BYTES_BEFORE_RESEED 1600000 | ||
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struct arc4_stream { | ||
unsigned char i; | ||
unsigned char j; | ||
unsigned char s[256]; | ||
}; | ||
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static int rs_initialized; | ||
static struct arc4_stream rs; | ||
static pid_t arc4_stir_pid; | ||
static int arc4_count; | ||
static int arc4_seeded_ok; | ||
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static inline unsigned char arc4_getbyte(void); | ||
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static inline void | ||
arc4_init(void) | ||
{ | ||
int n; | ||
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for (n = 0; n < 256; n++) | ||
rs.s[n] = n; | ||
rs.i = 0; | ||
rs.j = 0; | ||
} | ||
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static inline void | ||
arc4_addrandom(const unsigned char *dat, int datlen) | ||
{ | ||
int n; | ||
unsigned char si; | ||
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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; | ||
} | ||
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#ifndef WIN32 | ||
static ssize_t | ||
read_all(int fd, unsigned char *buf, size_t count) | ||
{ | ||
size_t numread = 0; | ||
ssize_t result; | ||
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while (numread < count) { | ||
result = read(fd, buf+numread, count-numread); | ||
if (result<0) | ||
return -1; | ||
else if (result == 0) | ||
break; | ||
numread += result; | ||
} | ||
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return (ssize_t)numread; | ||
} | ||
#endif | ||
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/* This is adapted from Tor's crypto_seed_rng() */ | ||
static int | ||
arc4_seed(void) | ||
{ | ||
unsigned char buf[ADD_ENTROPY]; | ||
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/* local variables */ | ||
#ifdef WIN32 | ||
static int provider_set = 0; | ||
static HCRYPTPROV provider; | ||
#else | ||
static const char *filenames[] = { | ||
"/dev/srandom", "/dev/urandom", "/dev/random", NULL | ||
}; | ||
int fd, i; | ||
size_t n; | ||
#endif | ||
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#ifdef WIN32 | ||
if (!provider_set) { | ||
if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL, | ||
CRYPT_VERIFYCONTEXT)) { | ||
if ((unsigned long)GetLastError() != (unsigned long)NTE_BAD_KEYSET) | ||
return -1; | ||
} | ||
provider_set = 1; | ||
} | ||
if (!CryptGenRandom(provider, sizeof(buf), buf)) | ||
return -1; | ||
arc4_addrandom(buf, sizeof(buf)); | ||
memset(buf, 0, sizeof(buf)); | ||
arc4_seeded_ok = 1; | ||
return 0; | ||
#else | ||
for (i = 0; filenames[i]; ++i) { | ||
fd = open(filenames[i], O_RDONLY, 0); | ||
if (fd<0) | ||
continue; | ||
n = read_all(fd, buf, sizeof(buf)); | ||
close(fd); | ||
if (n != sizeof(buf)) | ||
return -1; | ||
arc4_addrandom(buf, sizeof(buf)); | ||
memset(buf, 0, sizeof(buf)); | ||
arc4_seeded_ok = 1; | ||
return 0; | ||
} | ||
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return -1; | ||
#endif | ||
} | ||
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static void | ||
arc4_stir(void) | ||
{ | ||
int i; | ||
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if (!rs_initialized) { | ||
arc4_init(); | ||
rs_initialized = 1; | ||
} | ||
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arc4_seed(); | ||
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/* | ||
* Discard early keystream, as per recommendations in | ||
* "Weaknesses in the Key Scheduling Algorithm of RC4" by | ||
* Scott Fluhrer, Itsik Mantin, and Adi Shamir. | ||
* http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps | ||
* | ||
* Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that | ||
* we drop at least 2*256 bytes, with 12*256 as a conservative | ||
* value. | ||
* | ||
* RFC4345 says to drop 6*256. | ||
* | ||
* At least some versions of this code drop 4*256, in a mistaken | ||
* belief that "words" in the Fluhrer/Mantin/Shamir paper refers | ||
* to processor words. | ||
* | ||
* We add another sect to the cargo cult, and choose 12*256. | ||
*/ | ||
for (i = 0; i < 12*256; i++) | ||
(void)arc4_getbyte(); | ||
arc4_count = BYTES_BEFORE_RESEED; | ||
} | ||
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static void | ||
arc4_stir_if_needed(void) | ||
{ | ||
pid_t pid = getpid(); | ||
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if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) | ||
{ | ||
arc4_stir_pid = pid; | ||
arc4_stir(); | ||
} | ||
} | ||
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static inline unsigned char | ||
arc4_getbyte(void) | ||
{ | ||
unsigned char si, sj; | ||
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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]); | ||
} | ||
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static inline unsigned int | ||
arc4_getword(void) | ||
{ | ||
unsigned int val; | ||
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val = arc4_getbyte() << 24; | ||
val |= arc4_getbyte() << 16; | ||
val |= arc4_getbyte() << 8; | ||
val |= arc4_getbyte(); | ||
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return val; | ||
} | ||
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#ifndef ARC4RANDOM_NOSTIR | ||
ARC4RANDOM_EXPORT int | ||
arc4random_stir(void) | ||
{ | ||
int val; | ||
_ARC4_LOCK(); | ||
val = arc4_stir(); | ||
_ARC4_UNLOCK(); | ||
return val; | ||
} | ||
#endif | ||
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#ifndef ARC4RANDOM_NOADDRANDOM | ||
ARC4RANDOM_EXPORT void | ||
arc4random_addrandom(const unsigned char *dat, int datlen) | ||
{ | ||
int j; | ||
_ARC4_LOCK(); | ||
if (!rs_initialized) | ||
arc4_stir(); | ||
for (j = 0; j < datlen; j += 256) { | ||
/* arc4_addrandom() ignores all but the first 256 bytes of | ||
* its input. We want to make sure to look at ALL the | ||
* data in 'dat', just in case the user is doing something | ||
* crazy like passing us all the files in /var/log. */ | ||
arc4_addrandom(dat + j, datlen - j); | ||
} | ||
_ARC4_UNLOCK(); | ||
} | ||
#endif | ||
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#ifndef ARC4RANDOM_NORANDOM | ||
ARC4RANDOM_EXPORT unsigned int | ||
arc4random(void) | ||
{ | ||
unsigned int val; | ||
_ARC4_LOCK(); | ||
arc4_count -= 4; | ||
arc4_stir_if_needed(); | ||
val = arc4_getword(); | ||
_ARC4_UNLOCK(); | ||
return val; | ||
} | ||
#endif | ||
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ARC4RANDOM_EXPORT void | ||
arc4random_buf(void *_buf, size_t n) | ||
{ | ||
unsigned char *buf = _buf; | ||
_ARC4_LOCK(); | ||
arc4_stir_if_needed(); | ||
while (n--) { | ||
if (--arc4_count <= 0) | ||
arc4_stir(); | ||
buf[n] = arc4_getbyte(); | ||
} | ||
_ARC4_UNLOCK(); | ||
} | ||
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#ifndef ARC4RANDOM_NOUNIFORM | ||
/* | ||
* 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. | ||
*/ | ||
ARC4RANDOM_EXPORT unsigned int | ||
arc4random_uniform(unsigned int upper_bound) | ||
{ | ||
unsigned int r, min; | ||
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if (upper_bound < 2) | ||
return 0; | ||
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#if (UINT_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 | ||
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/* | ||
* 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; | ||
} | ||
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return r % upper_bound; | ||
} | ||
#endif |
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