The EnCase Evidence File Components and Function

The EnCase evidence file arrangement has what is described as “bag-and-tag” information which consists of information pertaining to case in the header of the file. In addition to the case information data, the image file also contains data and file integrity. Data and file integrity are very important when it come to ensuring the integrity and the proper authentication of the evidence image for court purposes. Message Digest 5 (MD5) and Cyclical Redundancy Check (CRC) are two functions that are used to provide these mechanisms within the EnCase evidence file.

MD5 is an algorithm that is used to verify data integrity through the creation of a 128-bit message digest from data input that is claimed to be as unique to that specific data as a fingerprint is to the specific individual. The result of the calculation is a 128-bit hexadecimal value which provides a number of possible values consisting of 2 ^128. This means that the odds of two files having the same MD5 value is 1 in 2^128. Because the chances are statically remote, the forensic community has adopted and accepted MD5 sufficient for forensic authentication.

CRC is similar in function and purpose to the MD5. The CRC algorithm results in a 32-bit hexadecimal value.

An EnCase evidence file has tree major components: the header, the data blocks and the file integrity component (CRC and MD5). The header will appear on the front end of the evidence file and the data blocks follow the header.

Any additional contribution towards this topic will help for those attempting to obtain the EnCE.

The EnCase Evidence File Format

The EnCase Evidence File Format

The EnCase evidence file can also be referred to as a forensic image file. The concept of an image file is where the entire drive contents of a target media is copied to a file and checksum values are calculated to verify the integrity (useful in court cases) of the image file (often referred to as a “hash value”). Forensic images are acquired with the use of software tools such as the UNIX “dd’ and FTK Imager as well as hardware were cloning devices such as the Solo Masster and Logicube’s MD5 have added forensic functionality.

One major difference between the above mentioned techniques to acquire image files and the EnCase image files is the “bag-and-tag” concept. The UNIX “dd” and many of the hardware cloning devices only provide the bit-for-bit information during acquisition. EnCase on the other hand provides the bit-for-bit data as well as additional data such as case information; data block integrity and file integrity to name a few. These functions are built into the EnCase imaging process for interoperability and ease of use. If the same function were to be implemented using the UNIX “dd” or the hardware options, this process would require many different tools and multiple steps to obtain the same results.

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