Writeblocking

Writeblocking, in digital forensics, is the practice of preventing writes to a storage device during acquisition to preserve evidence integrity. A write blocker is an intermediary device that sits between the evidence drive and the acquisition workstation; it allows read access to the drive while blocking write commands from the host, ensuring the original data remains unaltered. This is essential for maintaining chain of custody and the evidentiary admissibility of digital evidence.

There are hardware and software approaches. Hardware write blockers are dedicated devices compatible with interfaces such as USB, SATA, SCSI, or NVMe; they physically intercept or fail write requests while permitting reads. Software write blockers are components of forensic tools or operating-system policies that attempt to prevent writes, but they are generally considered less reliable than hardware blockers due to potential OS or driver interactions.

Usage typically involves connecting the evidence drive to the write blocker, then connecting the blocker to the acquisition workstation, and creating a forensic image of the drive. Verifications such as hash comparisons are performed to confirm data integrity. It is important to disable features that can cause writes, such as disk caching or TRIM on SSDs, and to follow manufacturer guidelines.

Limitations include possible bypasses on some devices, potential misconfiguration, and the fact that some hardware or firmware may still cause writes in edge cases. Therefore, practitioners should document the equipment used, perform health checks, and follow established standards such as ISO/IEC 27037 and relevant NIST guidelines.