Security Basics mailing list archives
Re: Rainbow table
From: "John Hummel" <john.c.hummel () gmail com>
Date: Tue, 22 Apr 2008 13:09:00 -0400
On Tue, Apr 22, 2008 at 10:43 AM, <koolanwar () gmail com> wrote:
How does Rainbow table Function. Please explain how reduction function computes hash value and then in the next stage generates a plain text. What Hash algorithms does Rainbow table use.
It doesn't - and anything you want. Let me put it this way. The point of a good hash algorithm is that you can't deduce the original from the hash value. So if you have: hash(x) = hashed_value_x hash(1) = abcajkl;ads hash(2) = 23478faadf .... So, looking at the values, you can't figure out what the hash value was before it was hashed. Now, a Rainbow Table approach says "Well, so I can't figure out what the original was based on the hash value. But - I can simply compute all possible values, get the hash, and store the result. Then, with the hash result, I can get the original. Not by applying an algorithm, but by simply looking up the hash in a table and seeing what the original was." So you supply the hash type - MD5, DES, SHA1 - whatever. Then all your rainbow table program is: int i = 0; while(1) { hashvalue = hash(i); insert into table Rainbow (i, hashvalue); i++; } You're not reducing anything - just letting the program run, and run, and run, and generate all possible values. Will this take some time? Oh, sure - it can take a long time, and take up oodles of hard drive space. Of course, if you distribute the algorithm a la the SETI project, then lots of people can work on various values and report back to a central location to make a big Rainbow Table, then distribute those gigabytes of data out there. Not that anyone would *do* that (yeah, right). This it the basic gist as I understand it. There's more detail than this, but basically it's just a giant while loop generating hashed values from the original and storing the result. -- John Hummel (813) 944-7064
Current thread:
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