Just a simple lookup table generation and search tool software.

We consider the problem of finding back a value from its hash (in the current implementation, MD5). Formally, we want to perform a preimage attack. Since hash functions are designed to be resistant to preimage attacks, we are often reduced to brute forcing: consider every single possible value, hash it and match it against the target hash. This is guaranteed to work but can take tremendeous amounts of time.

For feasible targets, we can speed up the process by storing the result of all these hashes in a (sorted) table. That way, whenever a new hash comes in, we simply have to look it up in the table. However, lookup tables tend to be huge and impractical.

C -> 12b2
B -> 3e4f
A -> 467f
D -> 8801

Here, the hash 0e4f would be easily mapped to the value B.

Generate a lookup table for 4 character words:

$ ./ltgen 4 a4.lt

Crack a value with this table:

% echo -n abcd | md5sum
e2fc714c4727ee9395f324cd2e7f331f  -
% ./ltcrack -x e2fc714c4727ee9395f324cd2e7f331f a4.lt 
e2fc714c4727ee9395f324cd2e7f331f abcd

You can benchmark by cracking for random values:

$ ./ltcrack -r 1000 a4.lt 
1000 / 1000

Note: since a lookup table contains all the possible values, a test should always validate completely

This program is distributed under the GPL licence (see LICENCE.md file). The credits for markdown formatting goes to https://github.com/IQAndreas/markdown-licenses