Digital Chain of Custody: Best Practices

The admissibility and evidentiary weight of digital evidence in Indian proceedings depends on two overlapping requirements: compliance with the certification standards under Section 57 of the Bharatiya Sakshya Adhiniyam, 2023 (BSA), and the integrity of the chain of custody from the moment of collection through to courtroom presentation. A digital chain of custody is the documented, unbroken record of who had control of a piece of evidence, when, how it was transferred, and what was done with it at each stage. When that chain is broken or successfully challenged, evidence that may be forensically compelling becomes legally useless. This article sets out the best practices that investigators, counsel, and forensic professionals should follow to ensure that digital evidence withstands scrutiny.

What Chain of Custody Means in Digital Forensics

In physical evidence management, chain of custody records the physical movement of an item between custodians. In digital forensics, the concept applies both to the storage media (the physical device) and to the forensic image (the bit-for-bit copy of that media) and any derivative work product extracted from it. Each transition — from device to forensic image, from image to analysis workstation, from analysis workstation to counsel, from counsel to court — must be documented with a date, time, the identity of the transferring and receiving persons, and the condition of the item at transfer. Where evidence is held on cloud infrastructure or third-party systems, the chain of custody must include the process by which data was extracted, the format of extraction, and confirmation that the data is complete and unaltered.

Hash Verification: The Technical Foundation

The integrity of a forensic image is established through cryptographic hash values. At the point of collection, the forensic examiner must compute the MD5 and SHA-256 hash values of the source media and of the forensic image created from it. Matching hash values confirm that the image is an exact, unaltered copy of the source at the time of collection. These values must be recorded in the collection log contemporaneously, signed by the examiner, and witnessed where practicable. Any subsequent examination must be conducted on a working copy — never on the master image — and the working copy must be independently hashed before and after analysis to confirm that no data was altered during examination.

Collection Logs and Documentation

Every step of the digital evidence collection process must be documented in a contemporaneous collection log recording: device description and serial number; date, time, and location of collection; the name and credentials of the forensic examiner; collection methodology and tool versions used; hash values computed; witness details; and packaging and labelling applied before storage. This log underpins the Section 57 BSA certificate. Inadequate or retrospectively prepared logs are among the most common grounds on which digital evidence is challenged in adversarial proceedings. Where evidence is obtained from a third-party service provider — cloud platform, email host, or telco — the process must include a production request under Section 94 of the Bharatiya Nagarik Suraksha Sanhita, 2023 (BNSS) where criminal proceedings are anticipated, with the provider’s response itself becoming part of the chain of custody record.

Storage, Access Control and Transfer

Once collected, forensic images and source devices must be stored in a secure, access-controlled environment that prevents tampering, environmental damage, or unauthorised access. Access must be logged electronically and in a physical register. Storage media should be protected against electrostatic discharge and magnetic interference. When evidence is transferred between custodians — from the investigating firm to outside counsel, or to a testifying expert — the transfer must be documented and the recipient must verify hash values to confirm that no data was altered in transit. Every person who takes custody of the evidence adds a link to the chain; every undocumented link is a vulnerability.

The Section 57 BSA Certificate

The certificate required under Section 57 of the Bharatiya Sakshya Adhiniyam, 2023 must attest that the computer or device was regularly used for lawful activities, was functioning normally during the relevant period, the electronic records were produced in the ordinary course of activity, and the information was not altered. For forensic evidence, the certificate should be signed by the forensic examiner or the head of the forensic laboratory — someone with direct knowledge of the collection methodology, the hash integrity of the image, and the absence of alteration. The Supreme Court in Arjun Panditrao Khotkar v. Kailash Kushanrao Gorantyal (2020) 7 SCC 1 made clear that this certificate is a mandatory pre-condition to admissibility, not a procedural formality. Certificates prepared by persons who lack direct knowledge of the collection and analysis process are routinely challenged and should not be relied upon.