Dans les affaires judiciaires, les juges confrontés à des questions d’ordre techniques en matière informatique, recourent à des experts qui mettent leur savoir-faire au service de la justice. Régulièrement mandatés par les tribunaux, ils ont pour mission d'éclairer le juge en apportant des éléments de preuve utiles à l'enquête.Ils recherchent dans les scellés informatiques les éléments relatifs aux faits incriminés en préservant l’intégrité des données et évitant toute altération des supports originaux. Les éléments de preuve ainsi recueillis sont analysés par l’expert qui déposera ses conclusions au magistrat sous forme d’un rapport d'expertise.les investigations techniques sont effectuées à l'aide des outils très sophistiqués qui permettent de prendre connaissance des informations présentes, effacées, cachées ou chiffrées dans les supports numériques examinés.Ce qui requiert une parfaite maîtrise du matériel déployé et une identification claire des bonnes pratiques de la discipline. Ce projet de recherches vise à mettre en exergue les défis techniques aux quels sont confrontés les experts, la complexité des outils utilisés dans le cadre des investigations techniques et l'importance de la mise en place des tests de validation qui permettent de connaître les capacités et limites de chaque outil. / In criminal cases, judges confronted with questions of technical order in computer technology, designate expert witnesses who put their expertise at the service of justice. Duly appointed by the courts, they help the judge by providing evidence relevant to the investigation.They search the suspect’s seized digital devices for elements of computer related crime, while preserving the integrity of the data and avoiding any alteration of the original media.The evidence thus collected is analyzed by a digital forensic expert who will document their findings to the judge in a report.Technical investigations are conducted by using powerful and sophisticated tools to find the current files and recover deleted, hidden or encrypted data from the digital media device examined.This requires perfect control of the utilized equipment and a clear identification of the methods used during the analysis. This research project aims to highlight the technical challenges which experts face, the complexity of digital forensic tools used for technical investigations, and the importance of their validation to understand the capabilities and limitations of each tool.

The area of digital forensics might be old but the idea that criminals or other organisations are actively working to hide their steps is somewhat new. Roughly a year ago, a company announced that they can actively exploit security flaws in a popular digital forensics suite, thus raising questions of validity of evidence submitted to court. It is not known if this exploit is being used in the wild but the mere thought of security issues existing in tools is a serious issue for law enforcement. This paper sets out to clarify the digital forensic process, what tools are used within the digital forensic process and what anti-forensic techniques are available on the market. Using the digital forensic process as a base, this paper produces a model that classifies anti-forensic techniques into realms and shows which realm affects which stage of the digital forensics process. The digital forensic process, anti-forensic techniques and the model was then tested in a Delphi-inspired study where questions regarding the digital forensic process and anti- forensic techniques was asked to digital forensic specialists as well as information security specialists. The goal of the Delphi-study was to reach a consensus regarding the foundations (process and techniques) and their internal relationships (as described in the model). The first part of this paper’s conclusion is that a digital forensic process should contain the following stages: Planning -> Identification -> Acquisition -> Analysis -> Presentation. The paper also concludes that there are several digital forensic tools available for a practitioner, both open and closed source, and that the practitioner uses a mixture of the two. Apart from the process and the tools used, this paper concludes that there are several anti-forensic techniques available on the market and that these could be used by any malicious user that actively want to disrupt the digital forensic process. A second conclusion is that the proposed model connects the stages of the digital forensic process with anti-forensic techniques though the use of realms. The proposed model can be used to develop anti-anti-forensics methods, processes or techniques.