MD5-string attack on web applications

Encryption Algorithm MD5, which is designed to create heshiv actively used in programming, particularly when developing Web applications as sekyuriti tool. In addition to its use to hash passwords as MD5 is used for other tasks related to security. For example, to generate a password when you install or create new accounts, or as a random string of names for files or folders.

Using the MD5 algorithm sekyuriti possible to use low-quality, leading to deteriorating security and web applications to the emergence of vulnerabilities in them. These disadvantages of using the MD5 algorithm I called MD5-string attack.

As I noted in 2008 - the output of MD5 algorithm alphabet has 16 characters. Therefore, when using, for example, function md5 (in PHP), at its output you get a string that consists of 16 characters md5-alphabet. And when using a short line, its reliability will nevylyka if you use this line for protective mechanisms (because it can be relatively easy to find).

Number of possible combinations depending on the length md5-line:

16 ^ 1 = 16
16 ^ 2 = 256
16 ^ 3 = 4096
16 ^ 4 = 65 536
16 ^ 5 = 1048576
16 ^ 6 = 16777216
16 ^ 7 = 268435456

Only at length md5-line in seven characters, its reliability bute acceptable (when used for protective mechanisms). If md5-line length less than 6, it can pick up relatively quickly.

Examples MD5-string attacks.

1. Using md5-string to create a password.

As in this engine (in versions of WordPress 2.0.x and potentially to 2.3.3 inclusive), during installation is given a weak password.

It consists of 6 characters md5-alphabet. Since the output function md5 in the alphabet have 16 characters, this password is 16777216 possible combinations. Брутфорсом And you can pick up relatively quickly.

2. Using md5-lines as the way to important resources.

As plug-in WordPress Database Backup feature md5 is used to create folders for backup.

The folder name appears as "backup-xxxxx" - a "backup-" and 5 md5-alphabet characters. And this is just 1048576 combinations. What can pick up relatively quickly.

So using the MD5 algorithm for protective mechanisms in web applications need to consider its alphabet. Because, in the case when using a short md5-string for a password (as WP), or folder name of backup database (both plugin WordPress Database Backup), it can be relatively quickly zabrutforsyty.