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File Example

Note: For brevity, all the provenance records and forensic actions are not shown.

This example shows how files, blocks of data and the relationships between them can be represented within the CASE ontology. By using a combination of Traces and Relationship objects it is possible to show the entire extraction of a file no matter the complexities of how it was stored.

This example shows a block of data that was extracted in the following way:

  1. A forensic image android_image is taken of an android device android_device1 and has been stored on an examiner's computer forensic_lab_computer1.
  2. A disk parition image_partition is carved from the image.
  3. A SQLite database sqlite_database is extracted from the disk partition.
  4. An encrypted SQLite blob sqlite_blob is extracted from the AttachmentTable of the SQLite database.
  5. The SQLite blob is AES decrypted resulting in a TAR archive decrypted_blob.
  6. A base64 encoded file tar_archive_file is extracted from the TAR archive.
  7. The TAR sub file is base64 decoded resulting in a JPG file decoded_attachment.
  8. A particular range of data chunk_of_data is extracted from the decoded JPG file.

Trace objects

The result of each step is represented with a Trace object characterizing the data (image, partition, file, database, chunk of data, etc.) that was exposed during the step. This Trace object contains property bundles that describe the data itself.

The most used property bundle will be ContentData. This property bundle will contain raw information about the data like byte order, hashes, size, as well as optionally include the data itself.

Another common property bundle used will be File. This property bundle will contain the file's metadata given to the file by the file system where it was found.

Relationship objects

The relationship between data resulting from a step and any data known previous to a step is represented by a Relationship object using one of the special keywords (contained-within, decrypted-from, decoded-from or stored-on). This object may contain property bundles that provide further detail on how the Trace pointed to by the source property is related to the Trace pointed to by the target property (e.g., where within the target was the source contained).

For the extraction of a file within a file system (EXT4, NTFS, TAR, etc) we use the property bundle PathRelation. This property bundle will contain file path information needed to extract the file out of the file system.

For encryption steps, we use the Encryption property bundle which provide the encryption algorithm and parameters that were utilized to decrypt the target file.

For encoding steps, we use the Encoding property bundle which provide the encoding algorithm used to decode the target file.

For the extraction of an embedded section of raw bytes within the target file, we use the DataRange property bundle which provides the offset location and range size within the target file.