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Crack (ZIP) passwords with John the Ripper

Feb 18 2015

Humans tend to forget. This is especially true for passswords! Forgetting zip passwords renders the zip file unuseable because it is not possible to recover the content of the zip file without the right password. So once in a while i have to crach my own passwords. I use the tool John the Ripper to recover the lost passwords. John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords.

Installation of JTR

I dont know if there is a package distribution of JTR for Ubuntu / Debian, so i decided to compile it by myself. Be sure that you have installed all needed libraries. In my case libssl-dev was missing and the first compilation attempt failes.

sudo apt-get install libssl-dev
wget http://www.openwall.com/john/j/john-1.8.0-jumbo-1.tar.xz
tar -xvf ./john-1.8.0-jumbo-1.tar.xz
cd john-1.8.0-jumbo-1/src

The previously shown installation downlods the libssl-dev package which is needed for the compilation of JTR. Build essentials have also to be installed, but i assume that you have already installed this package. The Next step is to download the sourcecode to the local directory and to unpack it. Finaly you run configure and make to compile it. On my machine the compilation took about 3 minutes. The result of the compilation will appear in the run folder.

A "make install" is not necessary for JTR.

If you start JTR without arguments then it prints its help and some configuration information:

$ ./john-1.8.0-jumbo-1/run/john
John the Ripper password cracker, version 1.8.0-jumbo-1_omp [linux-gnu 64-bit AVX-autoconf]
Copyright (c) 1996-2014 by Solar Designer and others
Homepage: http://www.openwall.com/john/

--single[=SECTION]        "single crack" mode
--wordlist[=FILE] --stdin wordlist mode, read words from FILE or stdin
                  --pipe  like --stdin, but bulk reads, and allows rules
--loopback[=FILE]         like --wordlist, but fetch words from a .pot file
--dupe-suppression        suppress all dupes in wordlist (and force preload)
--encoding=NAME           input encoding (eg. UTF-8, ISO-8859-1). See also
                          doc/ENCODING and --list=hidden-options.
--rules[=SECTION]         enable word mangling rules for wordlist modes
--incremental[=MODE]      "incremental" mode [using section MODE]
--mask=MASK               mask mode using MASK
--markov[=OPTIONS]        "Markov" mode (see doc/MARKOV)
--external=MODE           external mode or word filter
--stdout[=LENGTH]         just output candidate passwords [cut at LENGTH]
--restore[=NAME]          restore an interrupted session [called NAME]
--session=NAME            give a new session the NAME
--status[=NAME]           print status of a session [called NAME]
--make-charset=FILE       make a charset file. It will be overwritten
--show[=LEFT]             show cracked passwords [if =LEFT, then uncracked]
--test[=TIME]             run tests and benchmarks for TIME seconds each
--users=[-]LOGIN|UID[,..] [do not] load this (these) user(s) only
--groups=[-]GID[,..]      load users [not] of this (these) group(s) only
--shells=[-]SHELL[,..]    load users with[out] this (these) shell(s) only
--salts=[-]COUNT[:MAX]    load salts with[out] COUNT [to MAX] hashes
--save-memory=LEVEL       enable memory saving, at LEVEL 1..3
--node=MIN[-MAX]/TOTAL    this node's number range out of TOTAL count
--fork=N                  fork N processes
--pot=NAME                pot file to use
--list=WHAT               list capabilities, see --list=help or doc/OPTIONS
--format=NAME             force hash type NAME: 7z AFS agilekeychain aix-smd5
                          aix-ssha1 aix-ssha256 aix-ssha512 asa-md5 bcrypt
                          bfegg Bitcoin blackberry-es10 Blockchain bsdicrypt
                          chap Citrix_NS10 Clipperz cloudkeychain cq CRC32
                          crypt dahua descrypt Django django-scrypt dmd5 dmg
                          dominosec dragonfly3-32 dragonfly3-64 dragonfly4-32
                          dragonfly4-64 Drupal7 dummy dynamic_n eCryptfs EFS
                          eigrp EncFS EPI EPiServer fde FormSpring Fortigate
                          gost gpg HAVAL-128-4 HAVAL-256-3 hdaa HMAC-MD5
                          HMAC-SHA1 HMAC-SHA224 HMAC-SHA256 HMAC-SHA384
                          HMAC-SHA512 hMailServer hsrp IKE ipb2 KeePass
                          keychain keyring keystore known_hosts krb4 krb5
                          krb5-18 krb5pa-md5 krb5pa-sha1 kwallet LastPass LM
                          lotus5 lotus85 LUKS MD2 md4-gen md5crypt md5ns mdc2
                          MediaWiki MongoDB Mozilla mscash mscash2 MSCHAPv2
                          mschapv2-naive mssql mssql05 mssql12 mysql mysql-sha1
                          mysqlna net-md5 net-sha1 nethalflm netlm netlmv2
                          netntlm netntlm-naive netntlmv2 nk nsldap NT nt2
                          o5logon ODF Office oldoffice OpenBSD-SoftRAID
                          openssl-enc OpenVMS oracle oracle11 osc Panama
                          PBKDF2-HMAC-SHA1 PBKDF2-HMAC-SHA256
                          PBKDF2-HMAC-SHA512 PDF PFX phpass PHPS pix-md5 PKZIP
                          po postgres PST PuTTY pwsafe RACF RAdmin RAKP rar
                          RAR5 Raw-Blake2 Raw-Keccak Raw-Keccak-256 Raw-MD4
                          Raw-MD5 Raw-MD5u Raw-SHA Raw-SHA1 Raw-SHA1-Linkedin
                          Raw-SHA1-ng Raw-SHA224 Raw-SHA256 Raw-SHA256-ng
                          Raw-SHA384 Raw-SHA512 Raw-SHA512-ng ripemd-128
                          ripemd-160 rsvp Salted-SHA1 sapb sapg scrypt sha1-gen
                          sha1crypt sha256crypt sha512crypt Siemens-S7 SIP
                          skein-256 skein-512 skey Snefru-128 Snefru-256 SSH
                          SSH-ng SSHA512 STRIP SunMD5 sxc Sybase-PROP sybasease
                          tc_aes_xts tc_ripemd160 tc_sha512 tc_whirlpool
                          tcp-md5 Tiger tripcode VNC vtp wbb3 whirlpool
                          whirlpool0 whirlpool1 WoWSRP wpapsk xsha xsha512 ZIP

Crack the file

The next step is to crack the zip file (in my case the Bilder.zip).

$ ./zip2john ~/Bilder.zip > ~/Bilder.john
$ ./john --incremental ~/Bilder.john 

In the forst line JTR is extracting some data and the last line starts the brute-force attack against the zip file. This consumes a lot of CPU cycles - so it may be neccesary to adjust the niceness of the process. If you start JTR in the background then you can see the current status by adding the --status flag:

$ top
top - 21:25:22 up 22:14,  1 user,  load average: 0.86, 0.33, 0.17
Tasks:  88 total,   2 running,  86 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.5 us,  0.0 sy, 99.5 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   4049740 total,  3912160 used,   137580 free,   225840 buffers
KiB Swap:        0 total,        0 used,        0 free.  1477764 cached Mem

 5160 gue       39  19  223776  31612   2564 R 99.4  0.8   1:45.36 john
 5238 gue       20   0   24816   1524   1092 R  0.5  0.0   0:00.03 top
14795 snmp      20   0  114892   5988   2740 S  0.5  0.1   0:21.43 snmpd
$ ./john --status
0g 0:00:00:58  0g/s 1536p/s 1536c/s 1536C/s

The 0g in the status indicates that JTR has not found any matching password yet.

Final thoughts

Brute force attacks are not the cleverest way how to crack passwords but if you have enough time then this attempt will work. JTR is a great tool that is capable of doing a lot of other stuff like dictionary attacks and so on. Have a look in the FAQ.

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