How to use Rainbow Tables

Hi.

I have this script in Linux which finds a password by using brute force:

#!/bin/bash

space="a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z"

if [  $# -le 1 ]
then 
	echo "Usage: " $0 SALT PASSWORD_CODED
	exit
fi

for i in $space
do
for j in $space
do
for k in $space
do

	variable=$(openssl passwd -crypt -salt "$1" "$i$j$k")
	if [ "$variable" = $2 ]
	    then
		echo password found: $i$j$k
		exit
	fi
done
done
done

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If I execute it as:
 ./script ok okZdSfLRp/FqA

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then I get the password "abc".

However, if I execute it as:
./script vt vt/4.cscQFn1M

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then the program last a lot.

Is there a way to modify this script so it works quickly? Maybe using the Rainbow Tables technique? How can this be done?

Thank you
LVL 15
gplanaAsked:
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gheistCommented:
Second password is >wA
It took about one minute on NVIDIA ION2 (very old and slow HTPC GPU) to brute-force all 3-character DES passwords with the most popular password audit tool in the world - john the ripper.
gplanaAuthor Commented:
Thank you, but by the way the goal is not to get the password by John the ripper, but to understand how can it be get, or how can I modify my code to get it faster than now (even if it's not as fast as John the ripper).

Thank you.
serialbandCommented:
Rainbow tables are just pre-generated tables and you just do a match to it.  You'll have to generate a full table of possible passwords and just match it.

Your script will always be slower than a compiled cracker because it's spending its time calling another binary to check each hashed password, then closing it.
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gheistCommented:
You need to vectorize and parallelize loops, rainbow tables help only with fixed salt+popular password. bash cannot help to learn much, you need to learn C (without++) first.

(like oracle using salt "oracle", or access point name as part of WPA1 authentication)
computing DES is way faster than any memory access for a rainbow table lookup.

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gplanaAuthor Commented:
Can you explain a little more what is "vectorize and parallelize" ?
gheistCommented:
Please read GCC or CLANG documentation on topic. Nothing of that fixes bash scripts
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