Using Hash Table Generator

Configuration

Configuration for the Hash Generator determines what types of passwords to look for, and ultimately determines how long it will take to crack the passwords.

For Passwords, select a Character Set for the Hash Generator to crack. The following Character Sets are available:

• All - Searches all possible passwords using characters and symbols.
• Alpha - Searches passwords made up of the 26-character alphabet.
• Alpha-Numeric - Searches passwords made up of the 26 charcater alphabet and all numbers 0-9.
• Alpha-Numeric-Symbol14 - Searches passwords with a maximum lenght of 14 characters made up of the 26 character alphabet, all numbers 0-9, and all symbols.
• Alpha-Space - Searches passwords made up of the 26 character alphabet and spaces.

The characters sets are edited in the charset.txt file. Use the Edit button to bring up this file.

Minimum & Maximum lengths are the minimum and maximum length of a potential password. LM hashes can only be am maximum of 7 characters long. A windows password is composed of two hashes with a length of 7 which is how the total of 14 characters long is reached. There should be no need to change these values for most tables.

Chain Length: All precomputed hashes are not stored on disk as this would be prohibitive. Instead, chains are created where only the first and last hashes are stored to disk. The chain length is the “distance” between those two hashes. The longer a chain is, the higher the success rate of a table. At the same time, the longer a chain is, collisions increase and cracking time increases. Chain lengths should realistically stay between 2000-9000

Number of tables: Precomputed hash tables only have a certain probability. One can increase the total success rate by increasing the number of tables. L0phtCrack recommends the number of tables be between 3 and 9.

Chain count: Number of hash chains in a table. The more chains in a table, the better the success rate. File size also increases with chain count.

Sort tables: Before being used by LC, the precomputed tables need to be sorted. This option ensures they are as part of the generation process. There should be no need to disable this.

Results

This section is automatically updated to calculate disk space and success probability based on the configuration arguments. Disk space usage is only an estimate given compression variations.

The Generator's results are posted in a number of categories:

• Key Space - Key space is entirely driven by the character set and password length
• Total Success Rate - Total size and success rate are driven by table size, success rate and table count.
• Estimated Total Size - The size of the generated file the output for results.

Table

• Success Rate per Table - Measured in percentage.
• Estimated Table Size - Displays the size of the table.

Batch File

This section covers the maintenance of a batch file used to generate the appropriate tables.

You can dictate the Batch File Location and the Name of the Batch by typing in an address or click the button and Browse to the desired location.

• Generate - Generate is used to create the batch file based on the configuration options
• Run - Run will generate and execute the batch file
• Edit... - Edit the .bat file in Notepad.
• Quit - Exits the program.

The batch file approach is more flexible as table generation takes hours or even days. With the batch file, on can split it across multiple machines to parallelize the process.

The batch file scripts calls to 2 standalone processes: RTGEN to create the individual files and RTSORT to sort them. RTGEN and RTSORT can be interrupted at anytime. When restarted, they will automatically resume where stopped.

For more technical details there is a paper that describes the rainbow table implementation and goes into the tradeoffs, explaining chain length and chain count in detail.

Making a Faster Cryptanalytic Time-Memory Trade-Off