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review.gerrithub.io / AOSPAL / android_bionic / 081db840befec895fb86e709ae95832ade2d065c / . / libc / netbsd / resolv / res_random.c

/* $OpenBSD: res_random.c,v 1.17 2008/04/13 00:28:35 djm Exp $ */ | |

/* | |

* Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de> | |

* Copyright 2008 Damien Miller <djm@openbsd.org> | |

* Copyright 2008 Android Open Source Project (thread-safety) | |

* All rights reserved. | |

* | |

* Theo de Raadt <deraadt@openbsd.org> came up with the idea of using | |

* such a mathematical system to generate more random (yet non-repeating) | |

* ids to solve the resolver/named problem. But Niels designed the | |

* actual system based on the constraints. | |

* | |

* Later modified by Damien Miller to wrap the LCG output in a 15-bit | |

* permutation generator based on a Luby-Rackoff block cipher. This | |

* ensures the output is non-repeating and preserves the MSB twiddle | |

* trick, but makes it more resistant to LCG prediction. | |

* | |

* Redistribution and use in source and binary forms, with or without | |

* modification, are permitted provided that the following conditions | |

* are met: | |

* 1. Redistributions of source code must retain the above copyright | |

* notice, this list of conditions and the following disclaimer. | |

* 2. Redistributions in binary form must reproduce the above copyright | |

* notice, this list of conditions and the following disclaimer in the | |

* documentation and/or other materials provided with the distribution. | |

* | |

* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR | |

* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |

* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |

* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |

* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |

* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |

* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |

* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |

* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |

* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |

*/ | |

/* | |

* seed = random 15bit | |

* n = prime, g0 = generator to n, | |

* j = random so that gcd(j,n-1) == 1 | |

* g = g0^j mod n will be a generator again. | |

* | |

* X[0] = random seed. | |

* X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator | |

* with a = 7^(even random) mod m, | |

* b = random with gcd(b,m) == 1 | |

* m = 31104 and a maximal period of m-1. | |

* | |

* The transaction id is determined by: | |

* id[n] = seed xor (g^X[n] mod n) | |

* | |

* Effectivly the id is restricted to the lower 15 bits, thus | |

* yielding two different cycles by toggling the msb on and off. | |

* This avoids reuse issues caused by reseeding. | |

* | |

* The output of this generator is then randomly permuted though a | |

* custom 15 bit Luby-Rackoff block cipher. | |

*/ | |

#include <sys/types.h> | |

#include <netinet/in.h> | |

#include <sys/time.h> | |

#include "resolv_private.h" | |

#include <unistd.h> | |

#include <stdlib.h> | |

#include <string.h> | |

/* BIONIC-BEGIN */ | |

static pthread_mutex_t _res_random_lock = PTHREAD_MUTEX_INITIALIZER; | |

#define _RES_RANDOM_LOCK() pthread_mutex_lock(&_res_random_lock) | |

#define _RES_RANDOM_UNLOCK() pthread_mutex_unlock(&_res_random_lock) | |

/* BIONIC-END */ | |

#define RU_OUT 180 /* Time after wich will be reseeded */ | |

#define RU_MAX 30000 /* Uniq cycle, avoid blackjack prediction */ | |

#define RU_GEN 2 /* Starting generator */ | |

#define RU_N 32749 /* RU_N-1 = 2*2*3*2729 */ | |

#define RU_AGEN 7 /* determine ru_a as RU_AGEN^(2*rand) */ | |

#define RU_M 31104 /* RU_M = 2^7*3^5 - don't change */ | |

#define RU_ROUNDS 11 /* Number of rounds for permute (odd) */ | |

struct prf_ctx { | |

/* PRF lookup table for odd rounds (7 bits input to 8 bits output) */ | |

u_char prf7[(RU_ROUNDS / 2) * (1 << 7)]; | |

/* PRF lookup table for even rounds (8 bits input to 7 bits output) */ | |

u_char prf8[((RU_ROUNDS + 1) / 2) * (1 << 8)]; | |

}; | |

#define PFAC_N 3 | |

const static u_int16_t pfacts[PFAC_N] = { | |

2, | |

3, | |

2729 | |

}; | |

static u_int16_t ru_x; | |

static u_int16_t ru_seed, ru_seed2; | |

static u_int16_t ru_a, ru_b; | |

static u_int16_t ru_g; | |

static u_int16_t ru_counter = 0; | |

static u_int16_t ru_msb = 0; | |

static struct prf_ctx *ru_prf = NULL; | |

static long ru_reseed; | |

static u_int16_t pmod(u_int16_t, u_int16_t, u_int16_t); | |

static void res_initid(void); | |

/* | |

* Do a fast modular exponation, returned value will be in the range | |

* of 0 - (mod-1) | |

*/ | |

static u_int16_t | |

pmod(u_int16_t gen, u_int16_t exp, u_int16_t mod) | |

{ | |

u_int16_t s, t, u; | |

s = 1; | |

t = gen; | |

u = exp; | |

while (u) { | |

if (u & 1) | |

s = (s * t) % mod; | |

u >>= 1; | |

t = (t * t) % mod; | |

} | |

return (s); | |

} | |

/* | |

* 15-bit permutation based on Luby-Rackoff block cipher | |

*/ | |

u_int | |

permute15(u_int in) | |

{ | |

int i; | |

u_int left, right, tmp; | |

if (ru_prf == NULL) | |

return in; | |

left = (in >> 8) & 0x7f; | |

right = in & 0xff; | |

/* | |

* Each round swaps the width of left and right. Even rounds have | |

* a 7-bit left, odd rounds have an 8-bit left. Since this uses an | |

* odd number of rounds, left is always 8 bits wide at the end. | |

*/ | |

for (i = 0; i < RU_ROUNDS; i++) { | |

if ((i & 1) == 0) | |

tmp = ru_prf->prf8[(i << (8 - 1)) | right] & 0x7f; | |

else | |

tmp = ru_prf->prf7[((i - 1) << (7 - 1)) | right]; | |

tmp ^= left; | |

left = right; | |

right = tmp; | |

} | |

return (right << 8) | left; | |

} | |

/* | |

* Initializes the seed and chooses a suitable generator. Also toggles | |

* the msb flag. The msb flag is used to generate two distinct | |

* cycles of random numbers and thus avoiding reuse of ids. | |

* | |

* This function is called from res_randomid() when needed, an | |

* application does not have to worry about it. | |

*/ | |

static void | |

res_initid(void) | |

{ | |

u_int16_t j, i; | |

u_int32_t tmp; | |

int noprime = 1; | |

struct timeval tv; | |

ru_x = arc4random_uniform(RU_M); | |

/* 15 bits of random seed */ | |

tmp = arc4random(); | |

ru_seed = (tmp >> 16) & 0x7FFF; | |

ru_seed2 = tmp & 0x7FFF; | |

/* Determine the LCG we use */ | |

tmp = arc4random(); | |

ru_b = (tmp & 0xfffe) | 1; | |

ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M); | |

while (ru_b % 3 == 0) | |

ru_b += 2; | |

j = arc4random_uniform(RU_N); | |

/* | |

* Do a fast gcd(j,RU_N-1), so we can find a j with | |

* gcd(j, RU_N-1) == 1, giving a new generator for | |

* RU_GEN^j mod RU_N | |

*/ | |

while (noprime) { | |

for (i = 0; i < PFAC_N; i++) | |

if (j % pfacts[i] == 0) | |

break; | |

if (i >= PFAC_N) | |

noprime = 0; | |

else | |

j = (j + 1) % RU_N; | |

} | |

ru_g = pmod(RU_GEN, j, RU_N); | |

ru_counter = 0; | |

/* Initialise PRF for Luby-Rackoff permutation */ | |

if (ru_prf == NULL) | |

ru_prf = malloc(sizeof(*ru_prf)); | |

if (ru_prf != NULL) | |

arc4random_buf(ru_prf, sizeof(*ru_prf)); | |

gettimeofday(&tv, NULL); | |

ru_reseed = tv.tv_sec + RU_OUT; | |

ru_msb = ru_msb == 0x8000 ? 0 : 0x8000; | |

} | |

u_int | |

res_randomid(void) | |

{ | |

struct timeval tv; | |

u_int result; | |

_RES_RANDOM_LOCK() | |

gettimeofday(&tv, NULL); | |

if (ru_counter >= RU_MAX || tv.tv_sec > ru_reseed) | |

res_initid(); | |

/* Linear Congruential Generator */ | |

ru_x = (ru_a * ru_x + ru_b) % RU_M; | |

ru_counter++; | |

result = permute15(ru_seed ^ pmod(ru_g, ru_seed2 + ru_x, RU_N)) | ru_msb; | |

_RES_RANDOM_UNLOCK() | |

return result; | |

} | |

#if 0 | |

int | |

main(int argc, char **argv) | |

{ | |

int i, n; | |

u_int16_t wert; | |

res_initid(); | |

printf("Generator: %u\n", ru_g); | |

printf("Seed: %u\n", ru_seed); | |

printf("Reseed at %ld\n", ru_reseed); | |

printf("Ru_X: %u\n", ru_x); | |

printf("Ru_A: %u\n", ru_a); | |

printf("Ru_B: %u\n", ru_b); | |

n = argc > 1 ? atoi(argv[1]) : 60001; | |

for (i=0;i<n;i++) { | |

wert = res_randomid(); | |

printf("%u\n", wert); | |

} | |

return 0; | |

} | |

#endif | |