Password cracking is the process of recovering secret passwords from data that has been stored in or transmitted by a computer system. A common approach is to repeatedly try guesses for the password.
Most passwords can be cracked by using following techniques :
1) Hashing :- Here we will refer to the one way function (which may be either an encryption function or cryptographic hash) employed as a hash and its output as a hashed password.
If a system uses a reversible function to obscure stored passwords, exploiting that weakness can recover even 'well-chosen' passwords.
One example is the LM hash that Microsoft Windows uses by default to store user passwords that are less than 15 characters in length.
LM hash breaks the password into two 7-character fields which are then hashed separately, allowing each half to be attacked separately.
 | Hash functions like SHA-512, SHA-1, and MD5 are considered impossible to invert when used correctly. |
2) Guessing :- Many passwords can be guessed either by humans or by sophisticated cracking programs armed with dictionaries (dictionary based) and the user's personal information. Not surprisingly, many users choose weak passwords, usually one related to themselves in some way. Repeated research over some 40 years has demonstrated that around 40% of user-chosen passwords are readily guessable by programs. Examples of insecure choices include:
* blank (none)
* the word "password", "passcode", "admin" and their derivatives
* the user's name or login name
* the name of their significant other or another person (loved one)
* their birthplace or date of birth
* a pet's name
* a dictionary word in any language
* automobile licence plate number
* a row of letters from a standard keyboard layout (eg, the qwerty keyboard -- qwerty itself, asdf, or qwertyuiop)
* a simple modification of one of the preceding, such as suffixing a digit or reversing the order of the letters.
and so on....
In one survery of MySpace passwords which had been phished, 3.8 percent of passwords were a single word found in a dictionary, and another 12 percent were a word plus a final digit; two-thirds of the time that digit was.
| A password containing both uppercase & lowercase characters, numbers and special characters too; is a strong password and can never be guessed. |
| Check Your Password Strength |
|---|
| |
3) Default Passwords :- A moderately high number of local and online applications have inbuilt default passwords that have been configured by programmers during development stages of software. There are lots of applications running on the internet on which default passwords are enabled. So, it is quite easy for an attacker to enter default password and gain access to sensitive information. A list containing default passwords of some of the most popular applications is available on the internet.
| Always disable or change the applications' (both online and offline) default username-password pairs. |
4) Brute Force :- If all other techniques failed, then attackers uses brute force password cracking technique. Here an automatic tool is used which tries all possible combinations of available keys on the keyboard. As soon as correct password is reached it displays on the screen.This techniques takes extremely long time to complete, but password will surely cracked.
| Long is the password, large is the time taken to brute force it. |
5) Phishing :- This is the most effective and easily executable password cracking technique which is generally used to crack the passwords of e-mail accounts, and all those accounts where secret information or sensitive personal information is stored by user such as social networking websites, matrimonial websites, etc.
Phishing is a technique in which the attacker creates the fake login screen and send it to the victim, hoping that the victim gets fooled into entering the account username and password. As soon as victim click on "enter" or "login" login button this information reaches to the attacker using scripts or online form processors while the user(victim) is redirected to home page of e-mail service provider.
| Never give reply to the messages which are demanding for your username-password, urging to be e-mail service provider. |
It is possible to try to obtain the passwords through other different methods, such as social engineering, wiretapping, keystroke logging, login spoofing, dumpster diving, phishing, shoulder surfing, timing attack, acoustic cryptanalysis, using a Trojan Horse or virus, identity management system attacks (such as abuse of Self-service password reset) and compromising host security.
However, cracking usually designates a guessing attack.
-: Windows-XP Password Cracking :-
Here we use the tool "Cain and Abel" for cracking passwords of any local user/administrator.
First download cain and abel from "http://www.oxid.it/cain.html" and install it on your system.
Make sure that you have disabled the antivirus/firewall running on your system before installing and throughout this process.
Two most effective techniques used here are "Brute-Force" and "Cryptanalysis".
Brute-Force:- As this techniques takes more time to complete, the attacker prefer this technique only when there is a hope that the password contain same type of characters or may be two. i.e only loweralpha, only alpha, only numeric or may be loweralpha-numeric, also it should contain less than 7 characters. Otherwise it takes more time to crack password, which may be the mixture of all types of characters along with special symbols.
The step-by-step explaination for this technique is given below-
1) Open the tool "Cain and Abel"
2) Go into the category "Cracker"
it displays all sub-categories under "Cracker" in left panel.
3) Select "LM & NTLM Hashes" from left panel and then click on
symbol, you will be greeted by a window as shown.
4) Check "import hashes from local system" and then click "Next". This shows all the active accounts on local system like administrator, guest, etc. along with LM and NT hashed values of their respective passwords, as shown below.
5) Right clicking on any username shows all available options using which we can crack it's password.
6) Here we select "Brute-Force Attack" and then "NTLM Hashes", since windows uses NTLM hashes to store local users' passwords.
7) You will be greeted by a window where you can modify properties for brute-force attack such as password length, character set, etc.
8) Click on "Start" button.
9) On completion it will reveal the exact password.
-: Windows-XP Password Cracking :-
Cryptanalisys :- Basically, Cryptanalisys means Operations performed in converting encrypted messages to plain text without initial knowledge of the crypto-algorithm and/or key employed in the encryption.
This is the fastest technique of password cracking possible due to "Rainbow Tables".
A rainbow table is a file that is used to lookup an unknown plaintext from a known hash for an algorithm that does not usually permit this operation.
Steps 1 to 4 i.e upto importing hashes from local system, are similar to previous technique (i.e brute-force). The steps coming after that are as follows-
5) Here, select "cryptanalisys attack" then "NTLM hashes" and then select "via rainbow tables". Here we can choose either OphCrack or RainbowCrack formats of tables. The rainbow tables are available free to download on internet.
Due to large file size of rainbow tables (350MB - 3GB); instead of downloading we can also create at own just by downloading rainbow table generator (winrtgen.zip of 181KB) free download at "http://www.oxid.it/downloads/winrtgen.zip"
6) Click on "Add Table"
7) Browse for the location of rainbow table on your system, select proper table and click "open".
8) Select the loaded table and then click on "Start" button.
9) On completetion it will show the exact password.
| To learn windows password cracking techniques properly, one must understand "LM" & "NTLM" algorithms, SAM File, Dumping NTLM hashes from local SAM, Rainbow Tables, etc.......! |
0 comments:
Post a Comment