Add arc4random_buf and arc4random_uniform functions

Update arc4random module from FreeBSD.

Makefile

@@ -74,7 +74,9 @@ LIB_MANS_GEN := \
 LIB_MANS := \
 	arc4random.3 \
 	arc4random_addrandom.3 \
+	arc4random_buf.3 \
 	arc4random_stir.3 \
+	arc4random_uniform.3 \
 	strtonum.3 \
 	strlcpy.3 \
 	strlcat.3 \

Versions

@@ -60,5 +60,8 @@ LIBBSD_0.2 {
     pidfile_remove;
 
     setproctitle;
+
+    arc4random_buf;
+    arc4random_uniform;
 } LIBBSD_0.1;
 

src/arc4random.3

@@ -28,13 +28,15 @@
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
 .\" Manual page, using -mandoc macros
-.\" $FreeBSD: /repoman/r/ncvs/src/lib/libc/gen/arc4random.3,v 1.16 2003/07/31 06:18:24 das Exp $
+.\" $FreeBSD$
 .\"
 .Dd April 15, 1997
 .Dt ARC4RANDOM 3
 .Os
 .Sh NAME
 .Nm arc4random ,
+.Nm arc4random_buf ,
+.Nm arc4random_uniform ,
 .Nm arc4random_stir ,
 .Nm arc4random_addrandom
 .Nd arc4 random number generator
@@ -46,6 +48,10 @@
 .Ft u_int32_t
 .Fn arc4random "void"
 .Ft void
+.Fn arc4random_buf "void *buf" "size_t nbytes"
+.Ft u_int32_t
+.Fn arc4random_uniform "u_int32_t upper_bound"
+.Ft void
 .Fn arc4random_stir "void"
 .Ft void
 .Fn arc4random_addrandom "unsigned char *dat" "int datlen"
@@ -69,6 +75,21 @@ and therefore has twice the range of
 and
 .Xr random 3 .
 .Pp
+.Fn arc4random_buf
+function fills the region
+.Fa buf
+of length
+.Fa nbytes
+with ARC4-derived random data.
+.Pp
+.Fn arc4random_uniform
+will return a uniformly distributed random number less than
+.Fa upper_bound .
+.Fn arc4random_uniform
+is recommended over constructions like
+.Dq Li arc4random() % upper_bound
+as it avoids "modulo bias" when the upper bound is not a power of two.
+.Pp
 The
 .Fn arc4random_stir
 function reads data from
@@ -79,10 +100,9 @@ and uses it to permute the S-Boxes via
 There is no need to call
 .Fn arc4random_stir
 before using
-.Fn arc4random ,
-since
 .Fn arc4random
-automatically initializes itself.
+functions family, since
+they automatically initialize themselves.
 .Sh EXAMPLES
 The following produces a drop-in replacement for the traditional
 .Fn rand

src/arc4random.c

@@ -1,14 +1,23 @@
 /*
- * Arc4 random number generator for OpenBSD.
- * Copyright 1996 David Mazieres <dm@lcs.mit.edu>.
+ * Copyright (c) 1996, David Mazieres <dm@uun.org>
+ * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
  *
- * Modification and redistribution in source and binary forms is
- * permitted provided that due credit is given to the author and the
- * OpenBSD project (for instance by leaving this copyright notice
- * intact).
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
 /*
+ * Arc4 random number generator for OpenBSD.
+ *
  * 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
@@ -24,7 +33,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD: src/lib/libc/gen/arc4random.c,v 1.10 2004/03/24 14:44:57 green Exp $");
+__FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
 #include <sys/time.h>
@@ -40,6 +49,8 @@ struct arc4_stream {
 };
 
 #define	RANDOMDEV	"/dev/urandom"
+#define KEYSIZE		128
+
 #ifdef __REENTRANT
 static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
 #define	THREAD_LOCK()	pthread_mutex_lock(&arc4random_mtx)
@@ -52,58 +63,63 @@ static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
 static struct arc4_stream rs;
 static int rs_initialized;
 static int rs_stired;
+static int arc4_count;
 
-static inline u_int8_t arc4_getbyte(struct arc4_stream *);
-static void arc4_stir(struct arc4_stream *);
+static inline u_int8_t arc4_getbyte(void);
+static void arc4_stir(void);
 
 static inline void
-arc4_init(struct arc4_stream *as)
+arc4_init(void)
 {
 	int     n;
 
 	for (n = 0; n < 256; n++)
-		as->s[n] = n;
-	as->i = 0;
-	as->j = 0;
+		rs.s[n] = n;
+	rs.i = 0;
+	rs.j = 0;
 }
 
 static inline void
-arc4_addrandom(struct arc4_stream *as, u_char *dat, int datlen)
+arc4_addrandom(u_char *dat, int datlen)
 {
 	int     n;
 	u_int8_t si;
 
-	as->i--;
+	rs.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;
+		rs.i = (rs.i + 1);
+		si = rs.s[rs.i];
+		rs.j = (rs.j + si + dat[n % datlen]);
+		rs.s[rs.i] = rs.s[rs.j];
+		rs.s[rs.j] = si;
 	}
+	rs.j = rs.i;
 }
 
 static void
-arc4_stir(struct arc4_stream *as)
+arc4_stir(void)
 {
-	int     fd, n;
+	int done, fd, n;
 	struct {
-		struct timeval tv;
-		pid_t pid;
-		u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)];
-	}       rdat;
+		struct timeval	tv;
+		pid_t 		pid;
+		u_int8_t 	rnd[KEYSIZE];
+	} rdat;
 
-	gettimeofday(&rdat.tv, NULL);
-	rdat.pid = getpid();
 	fd = open(RANDOMDEV, O_RDONLY, 0);
+	done = 0;
 	if (fd >= 0) {
-		(void) read(fd, rdat.rnd, sizeof(rdat.rnd));
-		close(fd);
+		if (read(fd, &rdat, KEYSIZE) == KEYSIZE)
+			done = 1;
+		(void)close(fd);
 	} 
-	/* fd < 0?  Ah, what the heck. We'll just take whatever was on the
-	 * stack... */
+	if (!done) {
+		(void)gettimeofday(&rdat.tv, NULL);
+		rdat.pid = getpid();
+		/* We'll just take whatever was on the stack too... */
+	}
 
-	arc4_addrandom(as, (void *) &rdat, sizeof(rdat));
+	arc4_addrandom((u_char *)&rdat, KEYSIZE);
 
 	/*
 	 * Throw away the first N bytes of output, as suggested in the
@@ -113,33 +129,34 @@ arc4_stir(struct arc4_stream *as)
 	 * by Ilya Mironov.
 	 */
 	for (n = 0; n < 1024; n++)
-		arc4_getbyte(as);
+		(void) arc4_getbyte();
+	arc4_count = 1600000;
 }
 
 static inline u_int8_t
-arc4_getbyte(struct arc4_stream *as)
+arc4_getbyte(void)
 {
 	u_int8_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;
+	rs.i = (rs.i + 1);
+	si = rs.s[rs.i];
+	rs.j = (rs.j + si);
+	sj = rs.s[rs.j];
+	rs.s[rs.i] = sj;
+	rs.s[rs.j] = si;
 
-	return (as->s[(si + sj) & 0xff]);
+	return (rs.s[(si + sj) & 0xff]);
 }
 
 static inline u_int32_t
-arc4_getword(struct arc4_stream *as)
+arc4_getword(void)
 {
 	u_int32_t val;
 
-	val = arc4_getbyte(as) << 24;
-	val |= arc4_getbyte(as) << 16;
-	val |= arc4_getbyte(as) << 8;
-	val |= arc4_getbyte(as);
+	val = arc4_getbyte() << 24;
+	val |= arc4_getbyte() << 16;
+	val |= arc4_getbyte() << 8;
+	val |= arc4_getbyte();
 
 	return (val);
 }
@@ -148,55 +165,115 @@ static void
 arc4_check_init(void)
 {
 	if (!rs_initialized) {
-		arc4_init(&rs);
+		arc4_init();
 		rs_initialized = 1;
 	}
 }
 
-static void
+static inline void
 arc4_check_stir(void)
 {
-	if (!rs_stired) {
-		arc4_stir(&rs);
+	if (!rs_stired || arc4_count <= 0) {
+		arc4_stir();
 		rs_stired = 1;
 	}
 }
 
 void
-arc4random_stir()
+arc4random_stir(void)
 {
 	THREAD_LOCK();
 	arc4_check_init();
-	arc4_stir(&rs);
+	arc4_stir();
+	rs_stired = 1;
 	THREAD_UNLOCK();
 }
 
 void
-arc4random_addrandom(dat, datlen)
-	u_char *dat;
-	int     datlen;
+arc4random_addrandom(u_char *dat, int datlen)
 {
 	THREAD_LOCK();
 	arc4_check_init();
 	arc4_check_stir();
-	arc4_addrandom(&rs, dat, datlen);
+	arc4_addrandom(dat, datlen);
 	THREAD_UNLOCK();
 }
 
 u_int32_t
-arc4random()
+arc4random(void)
 {
 	u_int32_t rnd;
 
 	THREAD_LOCK();
 	arc4_check_init();
 	arc4_check_stir();
-	rnd = arc4_getword(&rs);
+	rnd = arc4_getword();
+	arc4_count -= 4;
 	THREAD_UNLOCK();
 
 	return (rnd);
 }
 
+void
+arc4random_buf(void *_buf, size_t n)
+{
+	u_char *buf = (u_char *)_buf;
+
+	THREAD_LOCK();
+	arc4_check_init();
+	while (n--) {
+		arc4_check_stir();
+		buf[n] = arc4_getbyte();
+		arc4_count--;
+	}
+	THREAD_UNLOCK();
+}
+
+/*
+ * Calculate a uniformly distributed random number less than upper_bound
+ * avoiding "modulo bias".
+ *
+ * Uniformity is achieved by generating new random numbers until the one
+ * returned is outside the range [0, 2**32 % upper_bound).  This
+ * guarantees the selected random number will be inside
+ * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
+ * after reduction modulo upper_bound.
+ */
+u_int32_t
+arc4random_uniform(u_int32_t upper_bound)
+{
+	u_int32_t r, min;
+
+	if (upper_bound < 2)
+		return (0);
+
+#if (ULONG_MAX > 0xffffffffUL)
+	min = 0x100000000UL % upper_bound;
+#else
+	/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
+	if (upper_bound > 0x80000000)
+		min = 1 + ~upper_bound;		/* 2**32 - upper_bound */
+	else {
+		/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
+		min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
+	}
+#endif
+
+	/*
+	 * This could theoretically loop forever but each retry has
+	 * p > 0.5 (worst case, usually far better) of selecting a
+	 * number inside the range we need, so it should rarely need
+	 * to re-roll.
+	 */
+	for (;;) {
+		r = arc4random();
+		if (r >= min)
+			break;
+	}
+
+	return (r % upper_bound);
+}
+
 #if 0
 /*-------- Test code for i386 --------*/
 #include <stdio.h>

src/arc4random_buf.3

@@ -0,0 +1 @@
+.so man3/arc4random.3

src/arc4random_uniform.3

@@ -0,0 +1 @@
+.so man3/arc4random.3