You are assigned to work in the computer forensics lab of a state police agency. While working on a high profile criminal case, you have followed every applicable procedure, however your boss is still concerned that the defense attorney might question whether evidence has been changed while at the lab. What can you do to prove that the evidence is the same as it was when it first entered the lab?

The standard and legally accepted method for verifying the integrity of digital evidence is cryptographic hashing. A hash function (such as MD5 or SHA) creates a unique, fixed-length digital fingerprint of the data. A hash value is calculated from the original evidence at the time of acquisition and documented in the chain of custody. To prove that the evidence has not been altered, the hash is recalculated at any later point. If the newly calculated hash matches the original hash, it provides strong, verifiable proof that the data remains identical and its integrity has been maintained.

B. The NIST National Software Reference Library (NSRL) database contains hashes of known files to help investigators filter out standard system files, not to verify the integrity of an entire evidence drive.
C. While lab certification attests to standardized procedures and quality management, it does not provide specific proof of integrity for an individual piece of evidence in a particular case.
D. A signed statement is a form of testimony, not empirical proof. This attestation must be supported by a verifiable technical process, such as the hashing method described in option A.

1. National Institute of Standards and Technology (NIST). (2006). Special Publication 800-86, Guide to Integrating Forensic Techniques into Incident Response.

Section 3.2.2, Data Collection, Page 17: "After the bit-stream image is created, a hash digest (e.g., MD5, SHA-1) of the image file should be created... The hash digest should be documented... This information is important in helping to prove that the copy is an exact duplicate of the original." This directly supports the process of creating and comparing hashes to prove integrity.

2. National Institute of Standards and Technology (NIST). (2014). Special Publication 800-101 Rev. 1, Guidelines on Mobile Device Forensics.

Section 4.3, Acquisition, Page 33: "A hash value of the acquired data from the mobile device should be created to help ensure the integrity of the data... The hash value can be used to show that the data has not been altered by the examination process by re-hashing the data and comparing it to the original hash value."

3. Carrier, B. (2005). File System Forensic Analysis. Addison-Wesley Professional.

Chapter 3, Volume Analysis, Section: Hashing, Page 81: "Hashing algorithms are used in computer forensics to show that a file or a hard disk has not been altered... If an investigation requires that a copy of a suspect disk be made, a hashing algorithm is applied to the original disk and the copy. If the values are the same, the copy is considered an exact duplicate." This is a foundational text used in university-level digital forensics courses.