[src/trunk]: src/lib/libc/gen discard first 256 words when we stir.

[itojun <itojun%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b607b2c08c85
branches:  trunk
changeset: 532748:b607b2c08c85
user:      itojun <itojun%NetBSD.org@localhost>
date:      Fri Jun 14 03:11:24 2002 +0000

description:
discard first 256 words when we stir.

diffstat:

 lib/libc/gen/arc4random.c |  11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diffs (32 lines):

diff -r b7c50b2a9e1d -r b607b2c08c85 lib/libc/gen/arc4random.c
--- a/lib/libc/gen/arc4random.c Fri Jun 14 03:05:46 2002 +0000
+++ b/lib/libc/gen/arc4random.c Fri Jun 14 03:11:24 2002 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: arc4random.c,v 1.2 2002/05/24 04:53:07 itojun Exp $    */
+/*     $NetBSD: arc4random.c,v 1.3 2002/06/14 03:11:24 itojun Exp $    */
 /*     $OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev Exp $ */
 
 /*
@@ -95,6 +95,7 @@
                struct timeval tv;
                u_int rnd[(128 - sizeof(struct timeval)) / sizeof(u_int)];
        }       rdat;
+       int     n;
 
        gettimeofday(&rdat.tv, NULL);
        fd = open("/dev/urandom", O_RDONLY);
@@ -124,6 +125,14 @@
         * 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);
 }
 
 static inline u_int8_t