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+
+/***************************************************************************
+ * nbase_rnd.c -- Some simple routines for obtaining random numbers for *
+ * casual use. These are pretty secure on systems with /dev/urandom, but *
+ * falls back to poor entropy for seeding on systems without such support. *
+ * *
+ * Based on DNET / OpenBSD arc4random(). *
+ * *
+ * Copyright (c) 2000 Dug Song <dugsong@monkey.org> *
+ * Copyright (c) 1996 David Mazieres <dm@lcs.mit.edu> *
+ * *
+ ***********************IMPORTANT NMAP LICENSE TERMS************************
+ *
+ * The Nmap Security Scanner is (C) 1996-2023 Nmap Software LLC ("The Nmap
+ * Project"). Nmap is also a registered trademark of the Nmap Project.
+ *
+ * This program is distributed under the terms of the Nmap Public Source
+ * License (NPSL). The exact license text applying to a particular Nmap
+ * release or source code control revision is contained in the LICENSE
+ * file distributed with that version of Nmap or source code control
+ * revision. More Nmap copyright/legal information is available from
+ * https://nmap.org/book/man-legal.html, and further information on the
+ * NPSL license itself can be found at https://nmap.org/npsl/ . This
+ * header summarizes some key points from the Nmap license, but is no
+ * substitute for the actual license text.
+ *
+ * Nmap is generally free for end users to download and use themselves,
+ * including commercial use. It is available from https://nmap.org.
+ *
+ * The Nmap license generally prohibits companies from using and
+ * redistributing Nmap in commercial products, but we sell a special Nmap
+ * OEM Edition with a more permissive license and special features for
+ * this purpose. See https://nmap.org/oem/
+ *
+ * If you have received a written Nmap license agreement or contract
+ * stating terms other than these (such as an Nmap OEM license), you may
+ * choose to use and redistribute Nmap under those terms instead.
+ *
+ * The official Nmap Windows builds include the Npcap software
+ * (https://npcap.com) for packet capture and transmission. It is under
+ * separate license terms which forbid redistribution without special
+ * permission. So the official Nmap Windows builds may not be redistributed
+ * without special permission (such as an Nmap OEM license).
+ *
+ * Source is provided to this software because we believe users have a
+ * right to know exactly what a program is going to do before they run it.
+ * This also allows you to audit the software for security holes.
+ *
+ * Source code also allows you to port Nmap to new platforms, fix bugs, and add
+ * new features. You are highly encouraged to submit your changes as a Github PR
+ * or by email to the dev@nmap.org mailing list for possible incorporation into
+ * the main distribution. Unless you specify otherwise, it is understood that
+ * you are offering us very broad rights to use your submissions as described in
+ * the Nmap Public Source License Contributor Agreement. This is important
+ * because we fund the project by selling licenses with various terms, and also
+ * because the inability to relicense code has caused devastating problems for
+ * other Free Software projects (such as KDE and NASM).
+ *
+ * The free version of Nmap is distributed in the hope that it will be
+ * useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Warranties,
+ * indemnification and commercial support are all available through the
+ * Npcap OEM program--see https://nmap.org/oem/
+ *
+ ***************************************************************************/
+
+/* $Id$ */
+
+#include "nbase.h"
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#if HAVE_SYS_TIME_H
+#include <sys/time.h>
+#endif /* HAV_SYS_TIME_H */
+#ifdef WIN32
+#include <wincrypt.h>
+#endif /* WIN32 */
+
+/* data for our random state */
+struct nrand_handle {
+ u8 i, j, s[256], *tmp;
+ int tmplen;
+};
+typedef struct nrand_handle nrand_h;
+
+static void nrand_addrandom(nrand_h *rand, u8 *buf, int len) {
+ int i;
+ u8 si;
+
+ /* Mix entropy in buf with s[]...
+ *
+ * This is the ARC4 key-schedule. It is rather poor and doesn't mix
+ * the key in very well. This causes a bias at the start of the stream.
+ * To eliminate most of this bias, the first N bytes of the stream should
+ * be dropped.
+ */
+ rand->i--;
+ for (i = 0; i < 256; i++) {
+ rand->i = (rand->i + 1);
+ si = rand->s[rand->i];
+ rand->j = (rand->j + si + buf[i % len]);
+ rand->s[rand->i] = rand->s[rand->j];
+ rand->s[rand->j] = si;
+ }
+ rand->j = rand->i;
+}
+
+static u8 nrand_getbyte(nrand_h *r) {
+ u8 si, sj;
+
+ /* This is the core of ARC4 and provides the pseudo-randomness */
+ r->i = (r->i + 1);
+ si = r->s[r->i];
+ r->j = (r->j + si);
+ sj = r->s[r->j];
+ r->s[r->i] = sj; /* The start of the the swap */
+ r->s[r->j] = si; /* The other half of the swap */
+ return (r->s[(si + sj) & 0xff]);
+}
+
+int nrand_get(nrand_h *r, void *buf, size_t len) {
+ u8 *p;
+ size_t i;
+
+ /* Hand out however many bytes were asked for */
+ for (p = buf, i = 0; i < len; i++) {
+ p[i] = nrand_getbyte(r);
+ }
+ return (0);
+}
+
+void nrand_init(nrand_h *r) {
+ u8 seed[256]; /* Starts out with "random" stack data */
+ int i;
+
+ /* Gather seed entropy with best the OS has to offer */
+#ifdef WIN32
+ HCRYPTPROV hcrypt = 0;
+
+ CryptAcquireContext(&hcrypt, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
+ CryptGenRandom(hcrypt, sizeof(seed), seed);
+ CryptReleaseContext(hcrypt, 0);
+#else
+ struct timeval *tv = (struct timeval *)seed;
+ int *pid = (int *)(seed + sizeof(*tv));
+ int fd;
+
+ gettimeofday(tv, NULL); /* fill lowest seed[] with time */
+ *pid = getpid(); /* fill next lowest seed[] with pid */
+
+ /* Try to fill the rest of the state with OS provided entropy */
+ if ((fd = open("/dev/urandom", O_RDONLY)) != -1 ||
+ (fd = open("/dev/arandom", O_RDONLY)) != -1) {
+ ssize_t n;
+ do {
+ errno = 0;
+ n = read(fd, seed + sizeof(*tv) + sizeof(*pid),
+ sizeof(seed) - sizeof(*tv) - sizeof(*pid));
+ } while (n < 0 && errno == EINTR);
+ close(fd);
+ }
+#endif
+
+ /* Fill up our handle with starter values */
+ for (i = 0; i < 256; i++) { r->s[i] = i; };
+ r->i = r->j = 0;
+
+ nrand_addrandom(r, seed, 128); /* lower half of seed data for entropy */
+ nrand_addrandom(r, seed + 128, 128); /* Now use upper half */
+ r->tmp = NULL;
+ r->tmplen = 0;
+
+ /* This stream will start biased. Get rid of 1K of the stream */
+ nrand_get(r, seed, 256); nrand_get(r, seed, 256);
+ nrand_get(r, seed, 256); nrand_get(r, seed, 256);
+}
+
+int get_random_bytes(void *buf, int numbytes) {
+ static nrand_h state;
+ static int state_init = 0;
+
+ /* Initialize if we need to */
+ if (!state_init) {
+ nrand_init(&state);
+ state_init = 1;
+ }
+
+ /* Now fill our buffer */
+ nrand_get(&state, buf, numbytes);
+
+ return 0;
+}
+
+int get_random_int() {
+ int i;
+ get_random_bytes(&i, sizeof(int));
+ return i;
+}
+
+unsigned int get_random_uint() {
+ unsigned int i;
+ get_random_bytes(&i, sizeof(unsigned int));
+ return i;
+}
+
+u64 get_random_u64() {
+ u64 i;
+ get_random_bytes(&i, sizeof(i));
+ return i;
+}
+
+
+u32 get_random_u32() {
+ u32 i;
+ get_random_bytes(&i, sizeof(i));
+ return i;
+}
+
+u16 get_random_u16() {
+ u16 i;
+ get_random_bytes(&i, sizeof(i));
+ return i;
+}
+
+u8 get_random_u8() {
+ u8 i;
+ get_random_bytes(&i, sizeof(i));
+ return i;
+}
+
+unsigned short get_random_ushort() {
+ unsigned short s;
+ get_random_bytes(&s, sizeof(unsigned short));
+ return s;
+}
+
+
+/* This function is magic ;-)
+ *
+ * Sometimes Nmap wants to generate IPs that look random
+ * but don't have any duplicates. The strong RC4 generator
+ * can't be used for this purpose because it can generate duplicates
+ * if you get enough IPs (birthday paradox).
+ *
+ * This routine exploits the fact that a LCG won't repeat for the
+ * entire duration of its period. An LCG has some pretty bad
+ * properties though so this routine does extra work to try to
+ * tweak the LCG output so that is has very good statistics but
+ * doesn't repeat. The tweak used was mostly made up on the spot
+ * but is generally based on good ideas and has been moderately
+ * tested. See links and reasoning below.
+ */
+u32 get_random_unique_u32() {
+ static u32 state, tweak1, tweak2, tweak3;
+ static int state_init = 0;
+ u32 output;
+
+ /* Initialize if we need to */
+ if (!state_init) {
+ get_random_bytes(&state, sizeof(state));
+ get_random_bytes(&tweak1, sizeof(tweak1));
+ get_random_bytes(&tweak2, sizeof(tweak2));
+ get_random_bytes(&tweak3, sizeof(tweak3));
+
+ state_init = 1;
+ }
+
+ /* What is this math crap?
+ *
+ * The whole idea behind this generator is that an LCG can be constructed
+ * with a period of exactly 2^32. As long as the LCG is fed back onto
+ * itself the period will be 2^32. The tweak after the LCG is just
+ * a good permutation in GF(2^32).
+ *
+ * To accomplish the tweak the notion of rounds and round keys from
+ * block ciphers has been borrowed. The only special aspect of this
+ * block cipher is that the first round short-circuits the LCG.
+ *
+ * This block cipher uses three rounds. Each round is as follows:
+ *
+ * 1) Affine transform in GF(2^32)
+ * 2) Rotate left by round constant
+ * 3) XOR with round key
+ *
+ * For round one the affine transform is used as an LCG.
+ */
+
+ /* Reasoning:
+ *
+ * Affine transforms were chosen both to make a LCG and also
+ * to try to introduce non-linearity.
+ *
+ * The rotate up each round was borrowed from SHA-1 and was introduced
+ * to help obscure the obvious short cycles when you truncate an LCG with
+ * a power-of-two period like the one used.
+ *
+ * The XOR with the round key was borrowed from several different
+ * published functions (but see Xorshift)
+ * and provides a different sequence for the full LCG.
+ * There are 3 32 bit round keys. This generator can
+ * generate 2^96 different sequences of period 2^32.
+ *
+ * This generator was tested with Dieharder. It did not fail any test.
+ */
+
+ /* See:
+ *
+ * http://en.wikipedia.org/wiki/Galois_field
+ * http://en.wikipedia.org/wiki/Affine_cipher
+ * http://en.wikipedia.org/wiki/Linear_congruential_generator
+ * http://en.wikipedia.org/wiki/Xorshift
+ * http://en.wikipedia.org/wiki/Sha-1
+ *
+ * http://seclists.org/nmap-dev/2009/q3/0695.html
+ */
+
+
+ /* First off, we need to evolve the state with our LCG
+ * We'll use the LCG from Numerical Recipes (m=2^32,
+ * a=1664525, c=1013904223). All by itself this generator
+ * pretty bad. We're going to try to fix that without causing
+ * duplicates.
+ */
+ state = (((state * 1664525) & 0xFFFFFFFF) + 1013904223) & 0xFFFFFFFF;
+
+ output = state;
+
+ /* With a normal LCG, we would just output the state.
+ * In this case, though, we are going to try to destroy the
+ * linear correlation between IPs by approximating a random permutation
+ * in GF(2^32) (collision-free)
+ */
+
+ /* Then rotate and XOR */
+ output = ((output << 7) | (output >> (32 - 7)));
+ output = output ^ tweak1; /* This is the round key */
+
+ /* End round 1, start round 2 */
+
+ /* Then put it through an affine transform (glibc constants) */
+ output = (((output * 1103515245) & 0xFFFFFFFF) + 12345) & 0xFFFFFFFF;
+
+ /* Then rotate and XOR some more */
+ output = ((output << 15) | (output >> (32 - 15)));
+ output = output ^ tweak2;
+
+ /* End round 2, start round 3 */
+
+ /* Then put it through another affine transform (Quick C/C++ constants) */
+ output = (((output * 214013) & 0xFFFFFFFF) + 2531011) & 0xFFFFFFFF;
+
+ /* Then rotate and XOR some more */
+ output = ((output << 5) | (output >> (32 - 5)));
+ output = output ^ tweak3;
+
+ return output;
+}
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