82 lines
1.8 KiB
C
82 lines
1.8 KiB
C
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/* rc4-based pseudo-random number generator for hping.
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* Copyright (C) 2003 Salvatore Sanfilippo
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* This software is released under the GPL license
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* All rights reserved */
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <sys/time.h>
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#include <time.h>
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u_int32_t hp_rand(void);
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/* The rc4 sbox */
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static unsigned char rc4_sbox[256];
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/* This flags is used to initialize the sbox the first time,
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* without an explicit intialization step outside this file. */
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static int rc4_seedflag = 0;
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/* Initialize the sbox with pseudo random data */
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static void hp_rand_init(void)
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{
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int i, fd;
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/* Strong sbox initialization */
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fd = open("/dev/urandom", O_RDONLY);
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if (fd != -1) {
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read(fd, rc4_sbox, 256);
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close(fd);
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}
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/* Weaker sbox initialization */
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for (i = 0; i < 256; i++) {
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struct timeval tv;
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gettimeofday(&tv, NULL);
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if (i&1)
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rc4_sbox[i] ^= (tv.tv_usec >> (i&0xF)) & 0xFF;
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else
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rc4_sbox[i] ^= (tv.tv_sec >> (i&0xF)) & 0xFF;
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}
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rc4_seedflag = 1;
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}
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#if 0
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/* Re-seed the generator with user-provided bytes. Not used for now. */
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static void hp_rand_seed(void *seed, size_t len)
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{
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int i;
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if (len > 256) len = 256;
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memcpy(rc4_sbox, seed, len);
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/* discard the first 256 bytes of output after the reseed */
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for (i = 0; i < 32; i++)
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(void) hp_rand();
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}
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#endif
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/* Generates a 32bit random number using an RC4-like algorithm */
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u_int32_t hp_rand(void)
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{
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u_int32_t r = 0;
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unsigned char *rc = (unsigned char*) &r;
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static unsigned int i = 0, j = 0;
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unsigned int si, sj, x;
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/* initialization, only needed the first time */
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if (!rc4_seedflag)
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hp_rand_init();
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/* generates 4 bytes of pseudo-random data using RC4 */
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for (x = 0; x < 4; x++) {
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i = (i+1) & 0xff;
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si = rc4_sbox[i];
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j = (j + si) & 0xff;
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sj = rc4_sbox[j];
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rc4_sbox[i] = sj;
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rc4_sbox[j] = si;
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*rc++ = rc4_sbox[(si+sj)&0xff];
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}
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return r;
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}
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