最近，有一些朋友問我一些軟件爆破后怎么還出現限制。我看了很多這類的軟件80%是使用MD5來防護的，國外的軟件使用率更高。
我現在說一說主流的應用方式，十個MD5中有九個是這樣應用的。
程序開篇就讀注冊表。
當我們輸入一個刺探碼時，程序會先一步把它寫入注冊表，不做變形，明碼的，在過去這樣的程序一般都是明碼比較的， 但現在遇到這樣的方式一般都是MD5. 

作者在程序中預置了一個目錄表，例如，21e47838e747ae8f380b253f0d8603f8； ...... 這類的密碼串。

你的刺探碼經過程序上MD5算法的加密也得到一個同樣長度的密碼串，然后拿這個密碼串與預置目錄中的進行比較，完全對應了就提示正確，不對應就提示出錯。并且有多個相同的預置目錄表散放在程序的各處，每執行到關鍵部分它就開始讀注冊表，進行加密和比較。很多的Cracker遇到這種MD5的加密方式都不知如何下手。其實了解了它的加密流程，就會發現它有一個致命的缺點，預置表就是它的軟肋，只要把刺探碼的對應MD5密碼串植入預置表即可。
所以現今一發現有上述注冊表操作的軟件，就應首先懷疑它是MD5防護的（過一段時間就不一定了）。

如果把這種加密方式放在網絡效驗軟件注冊上就不好辦了，我的P.C.L.s.G研究小組正在進行這方面探討，我希望這種方式將來能成為主流，下面我貼一個MD5的PHP實現（這是PHP小組定期發來的，所有的提及名字為PHP成員，而非P.C.L.s.G  ：））。

md5 add a note
+h+a+g+m+a+n+ at +h+o+t+b+r+e+v+ dot +c+o+m+
22-Jun-2003 10:05 
One char md5 bruteforce

function md5_bruteforce($md5_str)
{
 for ($i = 0; $i < 256; ++$i) {
      if ($md5_str == md5(chr($i))) {
          return chr($i);
      }
  }
 return false;
}
hkmaly at matfyz dot cz
20-Jun-2003 10:11 
You can use md5 (or other hash function) with xor even for symetric crypting and decrypting.

Michael Siroskey
19-Jun-2003 04:39 
The problem experienced by “lee at fallingforward dot net” was probably caused by using double quotes around the variable in Perl.  If double quotes are used (“$pa$$”) then Perl interprets syntax symbols ($, @) as variables for lookup.  In this case $$ will display the current pid for the running Perl process and not ‘$$’.  To prevent this from happening you either need to escape syntax symbols or you can use single quotes (‘$pa$$') to prevent it from doing variable lookup.  

# Incorrect Code
#--------------------------------------
$string = "pa$$";
require Digest::MD5;
$md5 = Digest::MD5->new;
$md5->add($string);
$digest = $md5->hexdigest;
print $digest,"\n";

# Correct Code
#--------------------------------------
$string = ‘pa$$’;
require Digest::MD5;
$md5 = Digest::MD5->new;
$md5->add($string);
$digest = $md5->hexdigest;
print $digest,"\n";

Hope this helps.

Michael Siroskey
Developer @ 2Checkout.com
Dream Master
28-May-2003 04:21 
I solved the problem....

Here is a link to my post on phpbb.com about a problem I was having with my perl script md5 encoding my data from within perl....

http://www.phpbb.com/phpBB/viewtopic.php?t=105334

Hope this helps someone...

----

Here's a copy just incase its removed from the phpbb.com site by the time you read this....

---CUT----

Posted: Wed May 28, 2003 3:09 am    Post subject: How to interface Perl with PHP's MD5 Password Encryption

Problem: Perl crypt and Php's use of MD5 are not compatible.

Encryption is more secure in MD5 as it is a ramdom set of 0-9 and a-f hashs in 64bits no matter what the length or text of the password. Perl's standard crypt cannot do this.

Solution: Within your perl script, just before the lines you are setting to write the password, you need to enter the following code.

Note: I tried this one Perl 5.006001 so it may not work on older versions.

--CLIP--

#load the MD5 Digest.
use Digest::MD5 qw(md5_hex);

#set your text databse variables to a single string for md5 conversion
#remember to change $database_array[1]; to your own variable.
$password = $database_array[1];

#generate yet another new string, this one is the converted database_array
#note the use of md5_hex

$newpassword = md5_hex($password);

#Send the $newpassword to your PHP SQL table and your set!

--CLIP--
I hope this helps out alot of people... from what I've read about this, no one else on the net could break this code... All it took was a little research, and brain work...

I am interested in your thoughts and comments on this... so please reply!!!

Good luck modding!!!
_________________
Dream Master
paj at pajhome dot org dot uk
21-May-2003 04:20 
Hi,

You can use the MD5 function in combination with a similar javascript function to protect user passwords for logins. The arrangement goes like this:

When the user requests the login page, the server generates a random number. It stores this in a session variable as well as sending to the client.

When the user clicks submit, javascript in the client computes md5(password + random).

The server can also generate this hash, because it already knows the password and random number. It uses this to check that the user entered the correct password.

The password has not been transmitted in the clear, and next login the random number will be different, so an attacker can't use a "replay attack".


Paul
Shane Allen
14-Apr-2003 09:53 
From the documentation on Digest::MD5:
md5($data,...)
This function will concatenate all arguments, calculate the MD5 digest of this "message", and return it in binary form.

md5_hex($data,...)
Same as md5(), but will return the digest in hexadecimal form.

PHP's function returns the digest in hexadecimal form, so my guess is that you're using md5() instead of md5_hex(). I have verified that md5_hex() generates the same string as PHP's md5() function.

(original comment snipped in various places)
>Hexidecimal hashes generated with Perl's Digest::MD5 module WILL
>NOT equal hashes generated with php's md5() function if the input
>text contains any non-alphanumeric characters.
>
>$phphash = md5('pa$$');
>echo "php original hash from text: $phphash";
>echo "md5 hash from perl: " . $myrow['password'];
>
>outputs:
>
>php original hash from text: 0aed5d740d7fab4201e885019a36eace
>hash from perl: c18c9c57cb3658a50de06491a70b75cd
lee at fallingforward dot net
07-Apr-2003 01:01 
There is an extremely frusturating incompatibility between php and Perl's md5() and crypt() functions. I hope someone can prove me wrong on this, because I'm having trouble finding any writing on the internet about it, yet it seems like a big problem.

Hexidecimal hashes generated with Perl's Digest::MD5 module WILL NOT equal hashes generated with php's md5() function if the input text contains any non-alphanumeric characters.

Example:

the correct password is "pa$$"

$hash = md5($password);
$phphash = md5('pa$$');

echo "plaintext password from user input: $password";
echo "hash from textfield: $hash";
echo "php original hash from text: $phphash";
echo "md5 hash from perl: " . $myrow['password'];

outputs:

plaintext password: pa$$
hash from textfield: 0aed5d740d7fab4201e885019a36eace
php original hash from text: 0aed5d740d7fab4201e885019a36eace
hash from perl: c18c9c57cb3658a50de06491a70b75cd
dmarsh dot no dot spam dot please at spscc dot ctc dot edu
02-Dec-2002 03:27 
Recommended readed: OpenSSL from O'reilly! It has chapters on SSL and PHP!! but it also covers cryptography in more depth (chapters 1 and 2 are highly recommended to all here!). It has lots of good information! Talks in depth about lots of stuff that I cannot begin to explain here.

MD5 is a repeatable hashes / digest process. Taking something of unknown size or content and reducing it to a known size but retaining a high degree of unknown content. A good hash / digest is said to alter the output significantly
changing ~50% of the bits in the "fixed-in-size" output stream) in the event of changing one bit (at random) from the "unknown-in-size" input stream (or even changing the length of the input stream by one bit*/byte, *=with padding if necessary)

MD5 is such a hash / digest. Other than that, it doesn't do much on it's own.

MD5 is a cheap way to test a file transfer (like a CRC32). If either the file or the MD5 is downloaded with errors, the chances that the MD5 of the file and the "PUBLIC" copy of the MD5 will match is highly unlikely. Both would have to error in a highly unpredictable way. However relying of MD5s as a way to validate that the file hasn't been tamptered with (tainted) is not good. If you can download the file from one place and a public MD5 from a second place, you at least are using a 3rd party method to attempt to validate the file's contents against tainting.

MD5 can ONLY be used to validate the contents against tainting if there is something secret (private) between the two end-points.

Lets examine MD5 in a typical and extremely effective email validating process. The two parties via a trusted method exchange a word / phrase / password (something private) that hopefully nobody else knows.

The first party publically composes an email with an MD5. But instead of sending that MD5. the MD5 is used against this word / phrase / password (private) in a Message Authentication Code (MAC), or better Hash-MAC (HMAC) 

One way would be to MD5 the word / phrase / password (private) part and the public part (the message body) as two different MD5's. the MD5 the two MD5s together as a single MD5 and send the composite MD5 in the public.

The receiver can (using all available parts, the private part, public part and the composite MD5) authenicate (testing against the computed part) the message hasn't been tampered during transit. The message body and the composite MD5 is sent in plain text, yet the contents have been authenicated with a high level of confidence. No encryption was used.

MD5 is often used to authenicate parts of encrypted streams and thus is the reason why many confuse MD5 as encryption (or even authenication) rather than what it is. A hash / digest.

An alternate to MD5 is SHA1. The output size of SHA1 is a little bigger (I think 164bits). More bits, means a higher degree of complexity. 128 bits is concidered minimim by experts in the field.... For cipher lengths and symmetric key sizes (due to computational power now available for brute force attacks).

--Doug
jason dot garber at vosystems dot biz
23-Oct-2002 12:46 
Just a quick note - To generate a random color for a webpage, use this

substr(md5(microtime()), 0, 6)

It will return a 6 char hex color.

-J
karlos dot gustavo at terra dot com dot br
30-Sep-2002 10:09 
simple slappaswd MD5 hash generation:

$ldap_passwd = "{md5}".base64_encode(pack("H*",md5($password)));
calin at ciao dot com
21-May-2002 07:01 
Hi everybody,

A way of partially securing your script so that a username/password combination is not visible immediatelly is to use the one-way-only encryption of md5. For example, using HTTP Authentication with PHP in this way:

if (
md5($PHP_AUTH_USER) !='21232f297a57a5a743894a0e4a801fc5' ||
md5($PHP_AUTH_PW) !='f70d11f8ad83b6f913115426098d2712'
) {
// force authentication
.....
exit;
}
could help you to protect the actual username and password from a person that can read the PHP script.

Calin Uioreanu
php9 Weblog
http://www.php9.com
mbabcock-php at fibrespeed dot net
27-Jun-2001 03:06 
I must point out to all the people who read the notes this far that MD5 is _not_ encryption in a traditional sense.  Creating an MD5 digest (or hash) of a message simply creates 128 bits that can be used to almost positively identify that message or object in the future.  You use MD5 if you want to validate that information is true.  For example, you may ask a user to submit a message through a browser POST and save an MD5 of that message in a database for a preview function.  When the user submits it the second time, running the MD5 hash of the new version of the text and comparing it to the original MD5 in the database will tell you if the text has changed at all.  This is how MD5 is used -- it is _not_ for encrypting things so as to get the data back afterward -- the MD5 hash version does _not_ contain the data of the original in a new form.