Posted onApr 2, 2020 • Edited onOct 28, 2020

Week 3: Introduction to John the Ripper

In your way through penetration testing, you will find yourself in situations where passwords or critical information are encoded. When this occurs, you first need to find in which format that hash is and then, try to decode it. For these cases, I like to useJohn the Ripper, one of the most popular password crackers around. So, let’s begin!

Formats

A format is just the kind of encoding that you’re trying to use. Let’s check how many formats john has by typingjohn --list=formats. You should see something like this:

j2rgez@myPC:~$john--list=formatsdescrypt, bsdicrypt, md5crypt, md5crypt-long, bcrypt, scrypt, LM, AFS,tripcode, AndroidBackup, adxcrypt, agilekeychain, aix-ssha1, aix-ssha256,aix-ssha512, andOTP, ansible, argon2, as400-des, as400-ssha1, asa-md5,AxCrypt, AzureAD, BestCrypt, bfegg, Bitcoin, BitLocker, bitshares, Bitwarden,BKS, Blackberry-ES10, WoWSRP, Blockchain, chap, Clipperz, cloudkeychain,dynamic_n, cq, CRC32, sha1crypt, sha256crypt, sha512crypt, Citrix_NS10,dahua, dashlane, diskcryptor, Django, django-scrypt, dmd5, dmg, dominosec,dominosec8, DPAPImk, dragonfly3-32, dragonfly3-64, dragonfly4-32,dragonfly4-64, Drupal7, eCryptfs, eigrp, electrum, EncFS, enpass, EPI,EPiServer, ethereum, fde, Fortigate256, Fortigate, FormSpring, FVDE, geli,gost, gpg, HAVAL-128-4, HAVAL-256-3, hdaa, hMailServer, hsrp, IKE, ipb2,itunes-backup, iwork, KeePass, keychain, keyring, keystore, known_hosts,krb4, krb5, krb5asrep, krb5pa-sha1, krb5tgs, krb5-17, krb5-18, krb5-3,kwallet, lp, lpcli, leet, lotus5, lotus85, LUKS, MD2, mdc2, MediaWiki,monero, money, MongoDB, scram, Mozilla, mscash, mscash2, MSCHAPv2,mschapv2-naive, krb5pa-md5, mssql, mssql05, mssql12, multibit, mysqlna,mysql-sha1, mysql, net-ah, nethalflm, netlm, netlmv2, net-md5, netntlmv2,netntlm, netntlm-naive, net-sha1, nk, notes, md5ns, nsec3, NT, o10glogon,o3logon, o5logon, ODF, Office, oldoffice, OpenBSD-SoftRAID, openssl-enc,oracle, oracle11, Oracle12C, osc, ospf, Padlock, Palshop, Panama,PBKDF2-HMAC-MD4, PBKDF2-HMAC-MD5, PBKDF2-HMAC-SHA1, PBKDF2-HMAC-SHA256,PBKDF2-HMAC-SHA512, PDF, PEM, pfx, pgpdisk, pgpsda, pgpwde, phpass, PHPS,PHPS2, pix-md5, PKZIP, po, postgres, PST, PuTTY, pwsafe, qnx, RACF,RACF-KDFAES, radius, RAdmin, RAKP, rar, RAR5, Raw-SHA512, Raw-Blake2,Raw-Keccak, Raw-Keccak-256, Raw-MD4, Raw-MD5, Raw-MD5u, Raw-SHA1,Raw-SHA1-AxCrypt, Raw-SHA1-Linkedin, Raw-SHA224, Raw-SHA256, Raw-SHA3,Raw-SHA384, ripemd-128, ripemd-160, rsvp, Siemens-S7, Salted-SHA1, SSHA512,sapb, sapg, saph, sappse, securezip, 7z, Signal, SIP, skein-256, skein-512,skey, SL3, Snefru-128, Snefru-256, LastPass, SNMP, solarwinds, SSH, sspr,Stribog-256, Stribog-512, STRIP, SunMD5, SybaseASE, Sybase-PROP, tacacs-plus,tcp-md5, telegram, tezos, Tiger, tc_aes_xts, tc_ripemd160, tc_ripemd160boot,tc_sha512, tc_whirlpool, vdi, OpenVMS, vmx, VNC, vtp, wbb3, whirlpool,whirlpool0, whirlpool1, wpapsk, wpapsk-pmk, xmpp-scram, xsha, xsha512, ZIP,ZipMonster, plaintext, has-160, HMAC-MD5, HMAC-SHA1, HMAC-SHA224,HMAC-SHA256, HMAC-SHA384, HMAC-SHA512, dummy, crypt

Wow, that’s a lot, right? Well, names and/or well-known formats (like MD5 which starts with $1$), could lead you to know which format you’re going to use. So let’s create a new file calledmy_hash.txt and insert the following hash (inuser:password format):root:$1$6ff3402b$2w6aUd7n//XodMXDt84BE1.

Now, to select the decoded format, we typejohn my_hash.txt --format=md5crypt and check the results:

j2rgez@myPC:~$john my_hash.txt--format=md5cryptUsing default input encoding: UTF-8Loaded 1 passwordhash(md5crypt, crypt(3)$1$(and variants)[MD5 256/256AVX28x3])Will run 12 OpenMP threadsProceeding with single, rules:SinglePress'q' or Ctrl-C to abort, almost any other keyforstatusAlmostdone: Processing the remaining buffered candidate passwords,ifany.Warning: Only 248 candidates bufferedforthe current salt, minimum 288 neededforperformance.Proceeding with wordlist:/usr/share/john/password.lst, rules:Wordlistadmin(root)1g 0:00:00:00 DONE 2/3(2020-04-02 20:38) 20.00g/s 90560p/s 90560c/s 90560C/s chacha..OU812Use the"--show" option to display all of the cracked passwords reliablySession completed

As you can see, john tried to find a match in its default wordlist and found it! The decoded value is “admin” (let's keep things fast).

There are tons of wordlists around the internet (or you can create your own ones). You can check for example the ones fromSecLists repo, and simply typejohn my_hash.txt --format=md5crypt --wordlist=my_wordlist.txt.

Automating all of this

So, last weekend I was completing some exercises from Pentesterlab when I found this sentence in one of the exercises:Use John by trial and error until you find the format. From the exercise context, you could imagine which format it was, but I was thinking: what if they ask me to do this in the future with a not so obvious format?

So I began my way of automating pentesting processes andcreated a new repo. Yes, I’m 90% sure that there is a better way (or an existing tool) to automate John the Ripper (or password cracking in general), but I find that it’s also a good way to practice some new programming languages or at least the ones that I don’t use on a day to day basis. So here is the first version of myjohn_auto_decypher.py script:

importsubprocessimportargparsedefdecrypt(formats,inputFile):keep_string="Press 'q' or Ctrl-C to abort, almost any other key for status"format=""forfinformats:try:decode_process=subprocess.check_output(["john",inputFile,"--format="+f],stdout=None)ifkeep_stringindecode_process:format=fexcept:subprocess.CalledProcessErrorifformat:print"Found a hash for "+format+" format"else:print"Couldn't decode, checking for already saved hashes..."printsubprocess.check_output(["john","--show",inputFile])defgetArgs():parser=argparse.ArgumentParser("john_auto_decypher.py")parser.add_argument("file",help="File with encoded passwords to be cracked",type=str)returnparser.parse_args()defmain():inputFile=getArgs().fileformats=map(lambdastr:str.strip(),subprocess.check_output(["john","--list=formats"]).split(","))decrypt(formats,inputFile)main()

Simple but effective, now by just typingpython john_auto_decypher.py <filename> on my CLI, this script will check all formats for me and/or already saved hashes. Of course, there is still a lot to improve, like adding parameters for wordlists andcustom rules.

So, that's all for today. Have a very good weekend you all!

Previous weeks:
Week 0: Security blog posts introduction
Week 1: Being conscious about your attack surface
Week 2: Knowing the penetration testing steps