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Cryptography deals with the subject of cracking the code of a program. In the sense of computer forensics it deals with information reading from a coded file. A task involved in computer forensics is to read the text of an encrypted file. The word cryptography is derived from a Greek word ‘kryptos’ which means hidden. The meaning of the word logy is study. Hence Cryptography means study of hidden data.

There were ciphers used for the purpose of encrypting information in a text file so that the unauthorized user is unable to understand it. Generally the origin of cryptography exists from a long time where the secret information was encoded and the same was decoded at the time of requirement. The application of cryptography is similar in the computer terminology. Here also the information is not available to an unauthorized person. The task of the computer forensics professional is to extract the information from an encoded file to form evidence.

More over there are many advantages of cryptography like it ensures confidentiality, integrity, authentication, etc. In case of computer forensics it is required for the computer professional to break the encoded information. The complexity of cryptanalysis of the data is dependent upon several factors. The most important among them are time, data and memory.

In relation of time factor the dependency is related as the number of primitive operations that need to be performed over the encrypted data text. The other factor over which cryptanalysis is dependent relates to data that will be required for performing the operations. It is dependent over the quantity of plain text that is required after breaking the cipher text. The most important is the memory in terms of storage capacity that is needed for performing the operation.

The success of cryptanalysis can be classified into several parts dependent upon the decryption carried out on the cipher text. The complete success or complete decryption relates when the forensics professional is able to read and decode the cipher text in entirety. If in case the attacker – computer forensics professional is capable of discovering a functionally equivalent code of the algorithm employed then it is referred to as global deduction.

In some cases it is also possible that the attacker is detected some additional cipher text or the plain text that was not known previously then it is known as instance local deduction. There are also many attacks that can be followed in order to decrypt the file. Some of the types include the Classical cryptanalysis - Frequency analysis and Kasiski examination.

There exist many other algorithms that can be used effectively to gain access to encrypted information. The Symmetric Algorithms like XSL attack, Differential cryptanalysis, Integral cryptanalysis, Mod-n cryptanalysis, Linear cryptanalysis, Slide attack, Statistical cryptanalysis can be used. Apart from these attacks some other related decryption techniques that can be used are Side-channel attack, Gardening (cryptanalysis), Birthday attack, Brute force attack, Differential Power Analysis, Man in the middle attack, Decipherment, Rubber-hose cryptanalysis.

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