Import cut down arc4ramdom.c from OpenBSD for better randomness.

Partially addresses #183.

diff --git a/compat/arc4random.c b/compat/arc4random.c
index 6524a8475be57e760a18c6e6767a84bbe83e119e..48ef29da4f545db466d2900698b98e238c947d8a 100644 (file)
--- a/compat/arc4random.c
+++ b/compat/arc4random.c
@@ -1,51 +1,158 @@
-/* 
- * dhcpcd - DHCP client daemon
- * Copyright (c) 2006-2009 Roy Marples <roy@marples.name>
- * All rights reserved
-
- * 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.
+/*
+ * Arc4 random number generator for OpenBSD.
+ * Copyright 1996 David Mazieres <dm@lcs.mit.edu>.
  *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
+ * Modification and redistribution in source and binary forms is
+ * permitted provided that due credit is given to the author and the
+ * OpenBSD project by leaving this copyright notice intact.
  */
 
+/*
+ * 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.
+ */
+
+#include <sys/time.h>
+
 #include <fcntl.h>
 #include <stdint.h>
 #include <stdlib.h>
-#include <time.h>
 #include <unistd.h>
 
 #include "arc4random.h"
 
-uint32_t arc4random(void)
+struct arc4_stream {
+       uint8_t i;
+       uint8_t j;
+       uint8_t s[256];
+};
+
+static int rs_initialized;
+static struct arc4_stream rs;
+static int arc4_count;
+
+static void
+arc4_init(struct arc4_stream *as)
+{
+       int n;
+
+       for (n = 0; n < 256; n++)
+               as->s[n] = n;
+       as->i = 0;
+       as->j = 0;
+}
+
+static void
+arc4_addrandom(struct arc4_stream *as, unsigned char *dat, int datlen)
+{
+       int n;
+       uint8_t si;
+
+       as->i--;
+       for (n = 0; n < 256; n++) {
+               as->i = (as->i + 1);
+               si = as->s[as->i];
+               as->j = (as->j + si + dat[n % datlen]);
+               as->s[as->i] = as->s[as->j];
+               as->s[as->j] = si;
+       }
+       as->j = as->i;
+}
+
+static uint8_t
+arc4_getbyte(struct arc4_stream *as)
+{
+       uint8_t si, sj;
+
+       as->i = (as->i + 1);
+       si = as->s[as->i];
+       as->j = (as->j + si);
+       sj = as->s[as->j];
+       as->s[as->i] = sj;
+       as->s[as->j] = si;
+       return (as->s[(si + sj) & 0xff]);
+}
+
+static uint32_t
+arc4_getword(struct arc4_stream *as)
+{
+       uint32_t val;
+
+       val = arc4_getbyte(as) << 24;
+       val |= arc4_getbyte(as) << 16;
+       val |= arc4_getbyte(as) << 8;
+       val |= arc4_getbyte(as);
+       return val;
+}
+
+static void
+arc4_stir(struct arc4_stream *as)
 {
        int fd;
-       static unsigned long seed;
-
-       if (seed == 0) {
-               fd = open("/dev/urandom", 0);
-               if (fd == -1 || read(fd,  &seed, sizeof(seed)) == -1)
-                       seed = time(0);
-               if (fd >= 0)
-                       close(fd);
-               srandom(seed);
+       struct {
+               struct timeval tv;
+               unsigned int rnd[(128 - sizeof(struct timeval)) /
+                       sizeof(unsigned int)];
+       }       rdat;
+       int n;
+
+       gettimeofday(&rdat.tv, NULL);
+       fd = open("/dev/urandom", O_RDONLY);
+       if (fd != -1) {
+               n = read(fd, rdat.rnd, sizeof(rdat.rnd));
+               close(fd);
        }
 
-       return (uint32_t)random();
+       /* fd < 0?  Ah, what the heck. We'll just take
+        * whatever was on the stack... */
+       arc4_addrandom(as, (void *) &rdat, sizeof(rdat));
+
+       /*
+        * Throw away the first N words of output, as suggested in the
+        * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
+        * by Fluher, Mantin, and Shamir.  (N = 256 in our case.)
+        */
+       for (n = 0; n < 256 * 4; n++)
+               arc4_getbyte(as);
+       arc4_count = 1600000;
+}
+
+void
+arc4random_stir()
+{
+
+       if (!rs_initialized) {
+               arc4_init(&rs);
+               rs_initialized = 1;
+       }
+       arc4_stir(&rs);
+}
+
+void
+arc4random_addrandom(unsigned char *dat, int datlen)
+{
+
+       if (!rs_initialized)
+               arc4random_stir();
+       arc4_addrandom(&rs, dat, datlen);
+}
+
+uint32_t
+arc4random()
+{
+
+       arc4_count -= 4;
+       if (!rs_initialized || arc4_count <= 0)
+               arc4random_stir();
+       return arc4_getword(&rs);
 }

diff --git a/compat/arc4random.h b/compat/arc4random.h
index 3b548af085b8fda4c5cee9fbc394519c1d8134fa..6f731092559f15a7db61f0dd9e0331d86b4219a5 100644 (file)
--- a/compat/arc4random.h
+++ b/compat/arc4random.h
@@ -30,5 +30,7 @@
 
 #include <stdint.h>
 
+void arc4random_stir(void);
+void arc4random_addrandom(unsigned char *, int);
 uint32_t arc4random(void);
 #endif