1 files changed, 228 insertions, 0 deletions

diff --git a/src/lib/libc/net/res_random.c b/src/lib/libc/net/res_random.c
new file mode 100644
index 0000000000..4dc1d33462
--- /dev/null
+++ b/src/lib/libc/net/res_random.c
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+/* $OpenBSD: res_random.c,v 1.16 2005/03/25 13:24:12 otto Exp $ */
+
+/*
+ * Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de>
+ * 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.
+ *
+ * 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 16 bit space is very small and brute force attempts are
+ * entirly feasible, we skip a random number of transaction ids
+ * so that an attacker will not get sequential ids.
+ */
+
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <sys/time.h>
+#include <resolv.h>
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+
+#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 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 long ru_reseed;
+static u_int32_t tmp;                /* Storage for unused random */
+static struct timeval tv;
+
+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);
+}
+
+/* 
+ * 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;
+        int noprime = 1;
+
+        tmp = arc4random();
+        ru_x = (tmp & 0xFFFF) % RU_M;
+
+        /* 15 bits of random seed */
+        ru_seed = (tmp >> 16) & 0x7FFF;
+        tmp = arc4random();
+        ru_seed2 = tmp & 0x7FFF;
+
+        tmp = arc4random();
+
+        /* Determine the LCG we use */
+        ru_b = (tmp & 0xfffe) | 1;
+        ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
+        while (ru_b % 3 == 0)
+                ru_b += 2;
+        
+        tmp = arc4random();
+        j = tmp % RU_N;
+        tmp = tmp >> 16;
+
+        /* 
+         * 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;
+
+        gettimeofday(&tv, NULL);
+        ru_reseed = tv.tv_sec + RU_OUT;
+        ru_msb = ru_msb == 0x8000 ? 0 : 0x8000; 
+}
+
+u_int
+res_randomid(void)
+{
+        int i, n;
+
+        gettimeofday(&tv, NULL);
+        if (ru_counter >= RU_MAX || tv.tv_sec > ru_reseed)
+                res_initid();
+
+#if 0
+        if (!tmp)
+                tmp = arc4random();
+
+        /* Skip a random number of ids */
+        n = tmp & 0x7; tmp = tmp >> 3;
+        if (ru_counter + n >= RU_MAX)
+                res_initid();
+#else
+        n = 0;
+#endif
+
+        for (i = 0; i <= n; i++)
+                /* Linear Congruential Generator */
+                ru_x = (ru_a * ru_x + ru_b) % RU_M;
+
+        ru_counter += i;
+
+        return (ru_seed ^ pmod(ru_g, ru_seed2 + ru_x, RU_N)) | ru_msb;
+}
+
+#if 0
+void
+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 = atoi(argv[1]);
+        for (i=0;i<n;i++) {
+                wert = res_randomid();
+                printf("%06d\n", wert);
+        }
+}
+#endif
+