How to crack encrypted zip file password using fcrackzip

Most common method for cracking passwords of such types of file are with Brute Force technique in which every combination of letters for a word are tested one by one. Although this method is very slow as because all combination are to be checked. But it is not impractical, as with some software it is possible.

The time consumed in cracking one password depends on the length of password, char. set used for password and on processing capabilities of system software,application software and your system configuration. So brute forcing time can be reduced by adding some conditions if we know nature of password. For example if the password is of 6 in length and it only contains digit, than these conditions can be defined in the application so that it can use only digits and exclude alphabets and symbols from its dictionary and searches only for 6 digit password, which increases the speed of searching.

There are many software present which can do this for you but the best one is fcrackzip as it is fast and free. fzcrack is available for both windows and linux.
fcrackzip implementation works tremendously faster on linux platforms comparing to windows one but you can use it on windows also. 
Its usage user interface is same for both platforms but installation is different.

For using it on windows, just download it and extract it.
Then open command prompt and change its directory to fcrackzip.exe, for example if your fcrackzip.exe is placed on your desktop than change your directory to desktop.
for this type cd [path] in cmd, for example if on desktop than type
 cd C:\Users\varun\Desktop\
Once you have done than continue with below dashed step

And for installing it on ubuntu just download it and than open terminal and use the below command
sudo aptitude install fcrackzip
 If you have backtrack than no need to download and install, it is preinstalled on it just go through
Applications>Backtrack>Privilege Escation>Pasword Hacks>Offline Attacks>chntpw

- Once you have completed the above steps for appropriate operating system than continue using it with following steps.
For using fcrackzip with brute force technique on file named sample.zip type the following command
fcrackzip -b [path for file sample.zip]
where fcrackzip remains the same for all commands but execution changes according to commands in between fcrqackzip and path which is -b for above command, which means brute force. Your can use following set if cammand for specifying conditions.
-h, --help
Prints the version number and (hopefully) some helpful insights.
-v, --verbose
Each -v makes the program more verbose.
-b, --brute-force
Select brute force mode. This tries all possible combinations of the letters you specify.
-D, --dictionary
Select dictionary mode. In this mode, fcrackzip will read passwords from a file, which must contain one password per line and should be alphabetically sorted (e.g. using (1)).
-c, --charset characterset-specification
Select the characters to use in brute-force cracking. Must be one of
a   include all lowercase characters [a-z]
  A   include all uppercase characters [A-Z]
  1   include the digits [0-9]
  !   include [!:$%&/()=?{[]}+*~#]
  :   the following characters upto the end of the spe-
      cification string are included in the character set.
      This way you can include any character except binary
      null (at least under unix).
-p, --init-password string
Set initial (starting) password for brute-force searching to string, or use the file with the name string to supply passwords for dictionary searching.
-l, --length min[-max]
Use an initial password of length min, and check all passwords upto passwords of length max (including). You can omit the max parameter.
-u, --use-unzip
Try to decompress the first file by calling unzip with the guessed password. This weeds out false positives when not enough files have been given.
-m, --method name
Use method number "name" instead of the default cracking method. The switch --help will print a list of available methods. Use --benchmark to see which method does perform best on your machine. The name can also be the number of the method to use.
-2, --modulo r/m
Calculate only r/m of the password. Not yet supported.
-B, --benchmark
Make a small benchmark, the output is nearly meaningless.
-V, --validate 
          Make some basic checks wether the cracker works.
 
For example, 
a1:$% selects lowercase characters, digits and the dollar and percent signs.
fcrackzip -b -c a1:$% -L 5 [path for encrypted zip file]
This will search for a password that is 5 in length and can contains a1:$% in its character.
 
Working Modes
BRUTE FORCE MODE 
By default, brute force starts at the given starting password, and successively tries all combinations until they are exhausted, printing all passwords that it detects, together with a rough correctness indicator. The starting password given by the -p switch determines the length. fcrackzip will not currently increase the password length automatically, unless the -l switch is used.

DICTIONARY MODE
This mode is similar to brute force mode, but instead of generating passwords using a given set of characters and a length, the passwords will be read from a file that you have to specify using the -p switch.

CP MASK
A CP mask is a method to obscure images or parts of images using a password. These obscured images can be restored even when saved as JPEG files. In most of these files the password is actually hidden and can be decoded easily (using one of the many available viewer and masking programs, e.g. xv). If you convert the image the password, however, is lost. The cpmask crack method can be used to brute-force these images. Instead of a zip file you supply the obscured part (and nothing else) of the image in the PPM-Image Format (xv and other viewers can easily do this). The cpmask method can only cope with password composed of uppercase letters, so be sure to supply the --charset A or equivalent option, together with a suitable initialization password. 

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