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From: Xin LI <delphij@FreeBSD.org>
Date: Tue, 14 Mar 2017 06:00:44 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r315225 - in head: lib/libc/gen sys/libkern
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Author: delphij
Date: Tue Mar 14 06:00:44 2017
New Revision: 315225
URL: https://svnweb.freebsd.org/changeset/base/315225

Log:
  Discard first 3072 bytes of RC4 keystream, this is a bandaid
  that allows us to work on switching to a more modern PRNG.
  
  Submitted by:	Steven Chamberlain <steven pyro eu org>
  Approved by:	so

Modified:
  head/lib/libc/gen/arc4random.c
  head/sys/libkern/arc4random.c

Modified: head/lib/libc/gen/arc4random.c
==============================================================================
--- head/lib/libc/gen/arc4random.c	Tue Mar 14 02:13:59 2017	(r315224)
+++ head/lib/libc/gen/arc4random.c	Tue Mar 14 06:00:44 2017	(r315225)
@@ -160,7 +160,7 @@ arc4_stir(void)
 	 * Discard early keystream, as per recommendations in:
 	 * "(Not So) Random Shuffles of RC4" by Ilya Mironov.
 	 */
-	for (i = 0; i < 1024; i++)
+	for (i = 0; i < 3072; i++)
 		(void)arc4_getbyte();
 	arc4_count = 1600000;
 }

Modified: head/sys/libkern/arc4random.c
==============================================================================
--- head/sys/libkern/arc4random.c	Tue Mar 14 02:13:59 2017	(r315224)
+++ head/sys/libkern/arc4random.c	Tue Mar 14 06:00:44 2017	(r315225)
@@ -84,11 +84,11 @@ arc4_randomstir(struct arc4_s* arc4)
 	/*
 	 * 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.)
+	 * by Fluher, Mantin, and Shamir.  (N = 768 in our case.)
 	 *
 	 * http://dl.acm.org/citation.cfm?id=646557.694759
 	 */
-	for (n = 0; n < 256*4; n++)
+	for (n = 0; n < 768*4; n++)
 		arc4_randbyte(arc4);
 
 	mtx_unlock(&arc4->mtx);