#27052 [Fbk->Opn]: rand() returns easily predictable numbers
ID: 27052
User updated by: webmaster at armondc dot com
Reported By: webmaster at armondc dot com
-Status: Feedback
+Status: Open
Bug Type: Math related
Operating System: Windows 2000 Professional
-PHP Version: 4.3.4
+PHP Version: 4.3.5RC2-dev
New Comment:
I tried it on 4.3.5RC2-dev, and it's still relativly the same. The
pattern is slightly different, but is still as predictable as before.
Previous Comments:
------------------------------------------------------------------------
[2004-01-26 19:04:34] sniper@php.net
Please try using this CVS snapshot:
http://snaps.php.net/php4-STABLE-latest.tar.gz
For Windows:
http://snaps.php.net/win32/php4-win32-STABLE-latest.zip
Some rand() related bugs have already been fixed..
------------------------------------------------------------------------
[2004-01-26 15:56:22] webmaster at armondc dot com
On the "actual result" its not as easily spotted without wrapping.
This should give a better picture:
]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F
[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F
[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F
[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F
[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F
[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F
[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F
[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\
------------------------------------------------------------------------
[2004-01-26 15:53:26] webmaster at armondc dot com
Description:
------------
I'm not sure if this is a very major problem, or even a bug, but here
goes:
It seems rand() on Windows is very predictable.
I've tried it on 2 Windows Systems, and they were both predictable. It
showed a breif unpredictable segment, then followed by the same string
of characters over and over, and finally a few more unpredictable
characters.
I tried this on a FreeBSD 5.2 System, and it was unpreditable enough.
Seems to be a windows-only problem.
I also noticed bug#11108 - It seems similar, but the submitter was
using his own seeds, and I am using without.
Reproduce code:
---------------
<?php
// This will reproduce the problem
// on windows
for($x = 0; $x < 500; $x++) {
echo chr((rand()%32)+65);
}
// This is a quick-fix, but
// goes agaist the documentation's
// 'no need for srand()'
for($x = 0; $x < 500; $x++) {
srand(hexdec(substr(md5(microtime()), 0, 8)));
echo chr((rand()%32)+65);
}
?>
Expected result:
----------------
Something a bit random like:
HEOSITFS[ZYH_EVIVVXSLCWRHHC_]_L^PIBTC\TXPBWQLCM^VZSUUHOG[\VF[KCDGFZM^Q\IG^KAIYPIYBSBIMGHXIBMPHLY\OAZMYAZPJ_DF\X\QXR[GP]DQLRHMYIOERBMEKBDJMJPN]J\\KPES^EGRKKO^S[XL\SSHQXOYQU_JDMMZEUEOQOYMHJPYDTRRU_URHYJGXRQYDYADD]OBVUGC^GGSXPRJJAOAKRAYYN^Q\XFQJNOWQKAJBFONFXNDZFFIMYRLROH^]IM_MINJI\MJJAVG]_B_EAVC\O_\DHCHLX_NIOU^KMJF\K]VZDOZ_FAWCZC_IQK^[NTPZCC]XEFZ[\AG[PV^XLPRYVAS]ZPH^WAXYAZYGK_M_QKF]PRMP^BBPTRV^KV_VDOLFIM]WQNHVF^DYWGGSGLJ_ZMODG[Z_AAXBYD^FS\MITLZESC`DXLH]NWNIVWZZMVMSXFQMG[O[W[YSPVMTQLHD
Actual result:
--------------
An easily spotted pattern:
]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\YRWXENCTQJOP]F[LIBGHU^SDAZ_MVK\
------------------------------------------------------------------------
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