Add sranddev() since srand() is not vary much with seed, typical time

2 files changed, 46 insertions, 1 deletions

diff --git a/lib/libc/stdlib/rand.3 b/lib/libc/stdlib/rand.3
index b47ff67..67955d9 100644
--- a/lib/libc/stdlib/rand.3
+++ b/lib/libc/stdlib/rand.3
@@ -42,6 +42,7 @@
 .Sh NAME
 .Nm rand ,
 .Nm srand ,
+.Nm sranddev ,
 .Nm rand_r
 .Nd bad random number generator
 .Sh LIBRARY
@@ -50,6 +51,8 @@
 .Fd #include <stdlib.h>
 .Ft void
 .Fn srand "unsigned seed"
+.Ft void
+.Fn sranddev void
 .Ft int
 .Fn rand void
 .Ft int
@@ -83,6 +86,13 @@ If no
 value is provided, the functions are automatically
 seeded with a value of 1.
 .Pp
+The
+.Fn sranddev
+routine initialize a seed using
+.Xr urandom 4
+random number device which returns good random numbers,
+suitable for cryptographic use.
+.Pp
 .Fn rand_r
 provides the same functionality as
 .Fn rand .
@@ -90,7 +100,8 @@ A pointer to the context value
 .Fa ctx
 must be supplied by the caller.
 .Sh SEE ALSO
-.Xr random 3
+.Xr random 3 ,
+.Xr urandom 4
 .Sh STANDARDS
 The
 .Fn rand
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c
index 70285bd..8de8ead 100644
--- a/lib/libc/stdlib/rand.c
+++ b/lib/libc/stdlib/rand.c
@@ -39,8 +39,11 @@
 static char sccsid[] = "@(#)rand.c	8.1 (Berkeley) 6/14/93";
 #endif /* LIBC_SCCS and not lint */
 
+#include <sys/time.h>          /* for sranddev() */
 #include <sys/types.h>
+#include <fcntl.h>             /* for sranddev() */
 #include <stdlib.h>
+#include <unistd.h>            /* for sranddev() */
 
 #ifdef TEST
 #include <stdio.h>
@@ -101,6 +104,37 @@ u_int seed;
 	next = seed;
 }
 
+
+/*
+ * sranddev:
+ *
+ * Many programs choose the seed value in a totally predictable manner.
+ * This often causes problems.  We seed the generator using the much more
+ * secure urandom(4) interface.
+ */
+void
+sranddev()
+{
+	int fd, done;
+
+	done = 0;
+	fd = _open("/dev/urandom", O_RDONLY, 0);
+	if (fd >= 0) {
+		if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
+			done = 1;
+		_close(fd);
+	}
+
+	if (!done) {
+		struct timeval tv;
+		unsigned long junk;
+
+		gettimeofday(&tv, NULL);
+		next = getpid() ^ tv.tv_sec ^ tv.tv_usec ^ junk;
+	}
+}
+
+
 #ifdef TEST
 
 main()