BASIC USAGE The Markov mode is based from [1], tested and applied to "classical" password cracking in [2]. This mode similar to the "wordlist" mode because it will only crack a fixed quantity of passwords. Specify the --markov option on the ommand line to use Markov mode. You can use any of these forms of the --markov option --markov[=LEVEL[:START[:END[:LENGTH]]]] --markov=MODE[:LEVEL[:START[:END[:LENGTH]]]] Where: * MODE is a particular Markov mode corresponding to a config file section [Markov:MODE]. The Markov mode name is not case sensitive. If the mode name is not specified, the default mode as specified in section [Markov:Default] is used. * LEVEL is the "Markov level". It can be specified as MIN_LEVEL-MAX_LEVEL or as MAX_LEVEL. MAX_LEVEL determines the maximum strength of passwords that are going to be cracked. When MAX_LEVEL increases, the quantity of passwords that are going to be tested increases exponentially. MIN_LEVEL determines the minimum strength of passwords that are generated. If LEVEL is 0 or not specified on the command line, the LEVEL interval is read from config variables in the [Markov:mode] section, or [Markov:Default] section if MODE is not specified on the command line, see CONFIGURATION OPTIONS. * START is the index of the first password that is going to be tested, starting with 0. Alternatively, you can specify an integer value < 100, followed by a percent sign, e.g. 10%. This will be converted into the correct start word depending on the total number of words. * END is the index of the last password that is going to be tested. When it is set to 0, it will represent the last possible password. Alternatively, you can specify an integer value <= 100, followed by a percent sign, e.g. 20%. This will be converted into the correct end word depending on the total number of words. * LENGTH determines the length of passwords generated. It can be specified as MIN_LENGTH-MAX_LENGTH or as MAX_LENGTH. MAX_LENGTH the maximum length of the tested passwords. MIN_LENGTH is the minimum length of the tested passwords. If LENGTH is 0 or not specified on the command line, the LENGTH interval is read from config variables in the [Markov:mode] section, or [Markov:Default] section if MODE is not specified on the command line, see CONFIGURATION OPTIONS. using --markov:100:0:0:12 will let john check every password whose length is 12 or less and whose "Markov strength" is 100 or less. SELECTING THE PARAMETERS The "LEVEL" parameter should be selected based on the desired maximum running time. In order to select the appropriate LEVEL, the following steps should be followed: 1/ Run the -single and -wordlist modes of john, as they will find many passwords for a low price 2/ Run john with a low markov level on the file, using the time utility. For example: ******************************************************************************* time john -markov:180 test Loaded 156 password hashes with no different salts (NT LM DES [128/128 BS SSE2]) Warning: MaxLen = 12 is too large for the current hash type, reduced to 7 MKV start (lvl=180 len=7 pwd=30449568) guesses: 0 time: 0:00:00:10 99% c/s: 475013K trying: real 0m10.707s user 0m10.621s sys 0m0.012s ******************************************************************************* This means that john can test 2.8M (30449568/10.707) passwords / seconds. It should be noted that with salted passwords the cracking speed will increase with every cracked password. This number should be corrected based on the experience of the user. 3/ Evaluate the quantity of passwords that could be cracked during the selected time. Using the previous example, a cracking time of 3 hours will lead to a quantity of passwords of 30714M passwords (30449568/10.707*3600*3). 4/ Use the genmkpwd command to find the corresponding level. Using the previous example, with a maximum password length of 12 (stupid because LM has a maximum length of 7 ...): ******************************************************************************* genmkvpwd stats 0 12 [...] lvl=245 (5904 Kb for nbparts) 26 G possible passwords (26528306250) lvl=246 (5928 Kb for nbparts) 29 G possible passwords (29373638087) lvl=247 (5952 Kb for nbparts) 32 G possible passwords (32524537496) [...] ******************************************************************************* Here, the selected level will be 246 (the higher level where the number of possible passwords is less than 30714M). 5/ Run john: ******************************************************************************* john -markov:246:0:0:12 test ******************************************************************************* DISTRIBUTING WORK The START and END parameter could be used to distribute work among many CPUs. The preferred method is to evaluate the combined cracking speed of all CPUs (adding the step 2 result for every CPUs available) and follow the previous method. At step 5, share the cracking space among all CPUs, where is share is proportionnal with the CPU's cracking speed. CONFIGURATION OPTIONS Default options for values not specified on the command line are available in the john.conf file. Unlike previous john versions which required these values to be specified in the general [Options] section, starting from this version, these values have to be specified in the [Markov:Default] secion, if MODE has not been specified on the command line. Otherwise the Markov options have to be specified in a config file section [Markov:MODE]. These are the values that can be specified: Statsfile - This is the path of the "stat" file. Specifying a Statsfile is mandatory for Markov mode, because the Statsfile cannot be specified as a command line parameter with --markov=<params>. MkvLvl - the default max. level MkvLvl should be specified, as a fallback for the maximum Markov level when using --markov or --markov=mode (without any additional parameters), or if the Markov level specified on the command line is 0. MkvMaxLen - the default max. length MkvMaxLen should also be specified, as a fallback for the maximum password length when using --markov or --markov=mode (without any additional parameters), --markov=<level> or --markov=mode:<level>, or similar options that don't include a value for the password length, or if the password length specified on the command line is 0. MkvMinLvl - the default min. level This value is used to determine the min. level if no Markov level was specified or if the Markov level specified on the command line was 0. (In other words, when the max. Markov level is read from the Markov mode section, the min. Markov level will be read from the Markov mode section as well.) If it is not found, the default min. Markov level will be 0. MkvMinLen - the default min. length This value is used to determine the min. length of passwords generated if no password length was specified or if the password length specified on the command line was 0. (In other words, when the max. password length is read from the Markov mode section, the min. password length will be read from the Markov mode section as well.) If it is not found, the default min. password length will be 0. WHAT IS THE STAT FILE? The markov mode is based on statistical data from real passwords. This data is stored in the "stat" file. In order to generate a custom stat file, it is recommanded to use the new calc_stat command: ./calc_stat <dictionary_file> stats MKVCALCPROBA USAGE This program is used to generate statistics about cracked passwords. It accepts as input the "stat" file and a file with a single cracked password per line. Here is a sample output: ******************************************************************************* ./mkvcalcproba stats /tmp/passwordlist test 33+16+28+20 97 4 40030907 45 password 29+16+30+22+51+25+24+30 227 8 2698006565378672 177 32'[[! 55+24+98+1000+23+29 1229 6 39949021871 1169 charsetsize = 92 ******************************************************************************* Its output is tab separated and should open nicely in spreadsheets. Here is the meaning of the column: 1/ Cracked password, reprinted from the file 2/ Sum of all "markov probabilities" of every letter of the word. This is supposed to help identify which parts of the password makes them strong. The number "1000" is written when no 1st/2nd letter combinations were found in the stat file (for exemple ' then [ here). 3/ Markov strength 4/ Password length 5/ Rank when bruteforced "stupidly" (a, b, c, ..., aa, ab, ac ...) considering that letters are ordered given their appearance probability and the given charsetsize (92) 6/ Markov strength of the password where the two first letters are removed REFERENCES [1] http://www.cs.utexas.edu/~shmat/shmat_ccs05pwd.ps [2] http://actes.sstic.org/SSTIC07/Password_Cracking/
