Computer Forensics & Data Recovery has articles on a wide variety of subjects relating to Computer Forensics - Data Recovery, Computer Crime, Cryptography, Freeware Computer Forensic Toolkit.

 

Fresh Advice:

Computer crashes are not an unknown phenomenon. They happen to every computer user at some point of time. To this end, now there are data recovery services available where each player in this market strives to do one better than the other in terms of services, maintenance contracts and other related aspects.

There are a lot of professional agencies who specialize in data recovery. VOGON is one such company which helps enterprises recover almost all its data and their software engineers have effective methods by which to do their job. They are into recovery, conversion and forensics.

DTI Data is another organization that promises excellent results on recovery of. It assures clients of competitive prices and solutions to a large variety of problems.

24-hour Data Recovery Systems is yet another company which claims a high success rate and touts its over-20 years' of experience in data recovery. Drive Solution Inc. claims to have the largest inventory of the various parts required in the event of physical damage. The company claims to be able to fix almost every problem known to the computer world. Burnt, wet, broken - they are confident they can fix anything that is even remotely salvageable. At a great price, too!

Cryptographic Methods

 

Caesar Cipher
The Caesar Cipher is a very simple cipher. It works by taking a message and incrementing each letter by a given amount. This amount is known as a shift. The advantage of this cipher is that the coded message is unreadable. However, if someone was to guess the shift value then the message would easily be decrypted.
Substitution Cipher
In the Caesar Cipher, with shift 6, each letter is replaced by the letter 6 further on in the alphabet. A substitution cipher has a different shift for each letter. The advantage of this cipher is that there are potentially 26! (26 x 25 x 24 ...) possible substitution ciphers. The disadvantage of the substitution cipher is that every letter is encrypted to the same letter, making it easy to pick out patterns in an encrypted message.


Vigenere Cipher

The Vigenere Cipher incorporates a table, which consists of A to Z written across the top and left hand side, and then the letters from A to Z shifted on each line. A keyword is chosen e.g. (VICTORY). The message is then compared with the keyword. The first letter from the message and keyword are read from the top and the right hand side of the table and the corresponding letter become the encrypted letter.

W E A R E T H E C H A M P I O N S O F T H E W O R L D
V I C T O R Y V I C T O R Y V I C T O R Y V I C T O R

R M C K S K F Z K J T A G G J V U H T K F Z E Q K Z U

The advantage of the Vigenere Cipher is that each letter is not always encrypted to the same letter each time. The disadvantage of this cipher is that given a long message, the keyword could be guessed by looking at patterns in the encrypted message.


Playfair Cipher
The Playfair Cipher relies on keyword and a 5 x 5 grid containing letters. The first blocks of the grid are filled with the letters of the keyword. The remaining blocks are filled with the remaining letters of the alphabet that were not present in the keyword. The message it put into a long string of letters and an X is placed between each pair of letters. For example, "MEET" would become "MEXET". The letters are then split in to pairs. These pairs are then referenced on the grid and a new pairs are derived. The advantage of the Playfair Cipher is that there are over 600 possibilities for pairs. The disadvantage of this cipher is that it can be cracked using a brute force algorithm due to the speed of modern computing power.


One-Time Pad
The one-time pad works in a similar way to the Vigenere Cipher. Whereas the Vigenere Cipher usually has a small keyword the one time pad key can be hundreds of pages of random letters. Both the sender and the receiver have a copy of the one-time pad (containing the long keyword). When a message is received it is decrypted using the applicable page within the pad. Normally, the first page of the book is used for the first message; the second page is used for the second message and so on. The advantage of the one-time pad is that it is completely unbreakable without the pad. The disadvantage of this method is that if one person loses the pad they can no longer decrypt messages that are sent to them.


Rotor Machines

A Rotor Machine consists of a number of rotors with 26 electrical contacts that correspond to a letter in the alphabet. When the rotor revolves, it changes the wiring amongst the electrical contacts and so the encryption is changed. This automates the act of changing the substitution at each stage of the encryption. Rotor machines commonly use three connected rotors, where the second rotor advances once when the first rotor makes one fully turn (26 advances). And so the third rotor advances once upon one full revolution of the second wheel. The advantage of the Rotor Machine is that a key length of 17,756 (26 x 26 x 26) can be achieved, making the encryption very difficult to crack. The disadvantage of this method, as the machine is automated, is that machine algorithm can be discovered making the code easier to crack.


Enigma

The Enigma Machine was an encryption machine, which used a 3-rotor system to encrypt letters. The second rotor would step an additional place every time the third rotor moved on, which made the key additionally hard to discover. The main disadvantage of the Enigma Machine was that a letter could never encrypt to itself. This helped towards breaking the Enigma code.

Cryptographic Methods - Posted on 10/1/2008

Computer Crime and Computer Forensics - Posted on 2/1/2008

The Freeware Forenic Toolkit - Posted on 6/12/2007

 

 

 

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