Wednesday, July 18, 2012

vortex5

Vortex level 5 consists in cracking a password hashed with MD5, which is called a preimage attack. No salt was used when applying the hash function, this makes it very easy by today's means to find the originating value.

The fastest way I found to achieve this is searching for the hash value with Google. Of course this will return lots of references to this level's solution, but you'll also get results for some websites that publish datasets of precomputed hashes, like for example md5crack or md5this.

Alternatively, you could crack the MD5 hash using some tool such as John The Ripper to perform a brute force attack. In the worst case this could result in computing all 62^5 combinations of the password (it was specified to be 5 characters long and consisting of a-zA-Z0-9). To restrict the number of tries, you can provide a wordlist of plausible passwords. Obviously, this will only generate a result if the password already existed in the list. This method works best when using real password data (e.g. from a leaked password database), since people tend to use similar patterns and also reuse their passwords.

Other tools such as RainbowCrack perform the attack using a rainbow table: a data structure used for the efficient storage of precomputed hash values. As for the websites mentioned above, you can easily get ahold of various tables, ranging from 50 to 500GB depending on the space of hashed values.