Sunday, October 21, 2012

Unprotect Excel Sheet with Brute-Force Attack and Masking Technique

MS Excel provide many features to manage and analyze large volume of data. Graphical representation tools and inbuilt (mathematical, financial, statistical and logical) functions make it very easy for everyone to analyze and summarize data without any special expertise. Besides so many user friendly features, MS Excel also provides a very useful security feature called “Password Protection” to prevent unauthorized access (or modification) of valuable data. This password protection feature of MS Excel allows User to protect entire workbook, individual sheet or cells of a file. 

Many times it happens that Excel user forget the password enabled by them to protect their worksheet. In such situation it is really very difficult to unprotect excel sheet without password remover software. I searched a lot to find methods of removing excel password without software but did not get even a single method which can do this. From my search I analysed that almost all the excel password remover software are based on two features: Brute-Force Attack Technique and Masking Technique.

Let me explain you how Brute-Force Attack and Masking Technique help to unprotect excel sheet. 

Brute-Force Attack Technique – This technique involves making all possible permutations of characters (lower case letters, upper case letters, special characters, numbers) of your password. All excel password breaker software provides you the option to specify the probable length and characters in your password. On the basis of the password length and characters all possible permutations are made and run through for checking. Total time taken by software to recover excel password directly depends on the total number of permutations (which in turn depends on the length and complexity of your password). 

For example if your password is 3 characters long and include numbers, Upper case and lower case letters then there will be total 62 * 62 * 62 = 238328 guesses or permutations (Here 62 = 26 lower case letters +26 upper case letters + 10 numbers).

Masking Technique – Many time it happens that user remember first few (or any) characters of their password but not able to recall full password. In such situation Masking Technique allows user to specify the initial (remember) characters and replace the unknown characters by '?'. This helps Brute-Force process to search for the unknown characters only and hence reduces the time to crack excel password. 

Overall we can say that because of Brute-Force Attack and Masking Technique excel password remover software has very high success rate. So, if you forget your excel file password then you can use any excel password recovery software based on Brute-Force Attack and Masking Technique.

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