I would like to add a little to what MSE has already said.
To bruteforce is to try every possible permuntation that a particular, usually encryption, algorithm can produce. I have written a DES brute force application before so I will use it as a reference.
DES is short for Data Encryption Standard
http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf and
http://en.wikipedia.org/wiki/Data_Encryption_Standard . Basically DES was created by the NSA as a standard encryption means for the US government. DES uses three elements, a 64-bit plain text, 64-bit key, and a 64-bit chipher text. The key and plain text is feed into the algorithm and the chipher text is the output. Another interesting point is that the 64-bit key is actually not 64 bits but 56-bit due to 8 parity bits.
So the question is this. There is a finite number of bit combinations that 56 bits can make. The combinations are 2^56 or 72057594037927936 keys to be tried.
To brute force an algorithm one must try every possible 72057594037927936 keys. This may seem imposible and it is without computers, and a lot of them. Simply start with the bit sequence of 0 and work you way to the end, ie:
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000001
00000000 00000000 00000000 00000000 00000000 00000000 00000010
00000000 00000000 00000000 00000000 00000000 00000000 00000011
...
11111111 11111111 11111111 11111111 11111111 11111111 11111110
11111111 11111111 11111111 11111111 11111111 11111111 11111111
This will give you every possible key and one of them WILL be correct. On average the result will be found in half the time it takes to compute the entire key space. In my results it would take 10,000 Penium 2.5GHz computers about 1.53 years to break a DES key. With specialized hardware the process can be scaled down to about 15 hours. Electronic Freedom Foundation, “Cracking DES: Secrets of Encryption Research, Wiretap Policies, and Chip Design,” 1999.
A simplier and more widely used method is to use word lists of common passwords. Instead of trying every possible combination, encode a word, compare it to the password hash and see if a match is present. One of the more common programs is John the Ripper www.openwall.com/john/ . John is portible across almost any platform including Linux and Windows.
If you want to brute force across the network you will need several proxies and an http brute forcer (I'm just assuming you want to crack website paswords).
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