Fcrackzip

FCRACKZIP - a Free/Fast Zip Password Cracker  

SYNOPSIS

 fcrackzip [-bDBchVvplum2] [--brute-force] [--dictionary] [--benchmark]
[--charset characterset] [--help] [--validate] [--verbose] [--init-password
string/path] [--length min-max] [--use-unzip] [--method name] [--modulo r/m]
file...  
DESCRIPTION

 fcrackzip searches each zipfile given for encrypted files and tries to guess
the password. All files must be encrypted with the same password, the more files
you provide, the better.  
OPTIONS


 -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).



 For example, a1:$% selects lowercase characters, digits and the dollar and
percent signs.
 -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.


  
ZIP PASSWORD BASICS

Have you ever mis-typed a password for unzip? Unzip reacted pretty fast with
'incorrect password', without decrypting the whole file. While the encryption
algorithm used by zip is relatively secure, PK made cracking easy by providing
hooks for very fast password-checking, directly in the zip file. Understanding
these is crucial to zip password cracking:

 For each password that is tried, the first twelve bytes of the file are
decrypted. Depending on the version of zip used to encrypt the file (more on
that later), the first ten or eleven bytes are random, followed by one or two
bytes whose values are stored elsewhere in the zip file, i.e. are known
beforehand. If these last bytes don't have the correct (known) value, the
password is definitely wrong. If the bytes are correct, the password might be
correct, but the only method to find out is to unzip the file and compare the
uncompressed length and crc's.

 Earlier versions of pkzip (1.xx) (and, incidentally, many zip clones for other
operating systems!) stored two known bytes. Thus the error rate was roughly
1/2^16 = 0.01%. PKWARE 'improved' (interesting what industry calls improved) the
security of their format by only including one byte, so the possibility of false
passwords is now raised to 0.4%. Unfortunately, there is no real way to
distinguish one byte from two byte formats, so we have to be conservative.  
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.  
EXAMPLES


 fcrackzip -c a -p aaaaaa sample.zip
 checks the encrypted files in sample.zip for all lowercase 6 character
passwords (aaaaaa ... abaaba ... ghfgrg ... zzzzzz).
 fcrackzip --method cpmask --charset A --init AAAA test.ppm
 checks the obscured image test.ppm for all four character passwords. -TP
fcrackzip -D -p passwords.txt sample.zip check for every password listed in the
file passwords.txt.


  
PERFORMANCE

 fzc, which seems to be widely used as a fast password cracker, claims to make
204570 checks per second on my machine (measured under plain dos w/o memory
manager).

 fcrackzip, being written in C and not in assembler, naturally is slower.
Measured on a slightly loaded unix (same machine), it's 12 percent slower (the
compiler used was pgcc, from http://www.gcc.ml.org/).

 To remedy this a bit, I converted small parts of the encryption core to x86
assembler (it will still compile on non x86 machines), and now it's about 4-12
percent faster than fzc (again, the fcrackzip performance was measured under a
multitasking os, so there are inevitably some meaurement errors), so there
shouldn't be a tempting reason to switch to other programs.

 Further improvements are definitely possible: fzc took 4 years to get into
shape, while fcrackzip was hacked together in under 10 hours. And not to forget
you have the source, while other programs (like fzc), even come as an encrypted
.exe file (maybe because their programmers are afraid of other people could
having a look at their lack of programming skills? nobody knows...)  
RATIONALE

The reason I wrote fcrackzip was NOT to have the fastest zip cracker available,
but to provide a portable, free (thus extensible), but still fast zip password
cracker. I was really pissed of with that dumb, nonextendable zipcrackers that
were either slow, were too limited, or wouldn't run in the background (say,
under unix). (And you can't run them on your superfast 600Mhz Alpha).  
BUGS

No automatic unzip checking.

 Stop/resume facility is missing.

 Should be able to distinguish between files with 16 bit stored CRC's and 8 bit
stored CRC's.

 The benchmark does not work on all systems.

 It's still early alpha.

 Method "cpmask" only accepts ppms.

 Could be faster.  
AUTHOR

 fcrackzip was written by Marc Lehmann <pcg()goof.com>. The main fcrackzip page
is at http://www.goof.com/pcg/marc/fcrackzip.html)