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FCRACKZIP(1) General Commands Manual FCRACKZIP(1) NAME 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-libzip] [--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 sort(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 dol- lar 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 dictio- nary 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-libzip Try to decompress the first file by calling libzip 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 --bench- mark 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 en- cryption 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 de- crypted. 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 com- pare 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 succes- sively tries all combinations until they are exhausted, printing all pass- words 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 pass- words 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 pass- word. 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-Im- age Format (xv and other viewers can easily do this). The cpmask method can only cope with password composed of uppercase let- ters, 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 charac- ter 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 pass- word 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 avail- able, 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) Free/Fast Zip Password Cracker FCRACKZIP(1)
NAME | SYNOPSIS | DESCRIPTION | ZIP PASSWORD BASICS | BRUTE FORCE MODE | DICTIONARY MODE | CP MASK | EXAMPLES | PERFORMANCE | RATIONALE | BUGS | AUTHOR
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