Chain of Custody: Understanding SHA-256 Hashing

Generative AI makes video easier to alter, so counsel need a way to show a deposition recording hasn't changed. SHA-256 hashing is how we do it.

Beyond the physical chain of custody

Historically, a chain of custody relied on physical media: locked filing cabinets, signed courier logs, and sealed VHS tapes or DVDs. Today, video files are transmitted via cloud links and stored on standard hard drives. To secure digital files, we must rely on mathematics rather than padlocks.

Developed by the National Security Agency (NSA), SHA-256 (Secure Hash Algorithm 256-bit) does not encrypt or "lock" the video file to prevent viewing. Instead, it acts as a fingerprint that changes if the file changes. The algorithm reads the underlying binary data of the video file and translates it into a unique, fixed-length string of 64 hexadecimal characters.

The avalanche effect

The core strength of SHA-256 in a litigation context is a principle known as the Avalanche Effect. In cryptography, this means that even the most microscopic alteration to the source file will produce a completely different hash.

Imagine someone edits out a single frame of a deposition, or applies an AI audio filter to slightly alter the tone of the deponent's voice. Even if this change is completely imperceptible to the human eye or ear, the foundational binary data of the file has shifted. If you were to run that altered video through the SHA-256 algorithm again, the new hash would look completely different from the original. It is computationally infeasible to alter the file while keeping the original fingerprint.

How to check a file later

Our hashing workflow gives you a verifiable record:

1. Same-day hashing: The same day the deposition is recorded, the master card is forensically imaged and hashed, before any post-processing.
2. Documentation: The hash values are recorded in a manifest kept with the masters. When the authentication package is ordered, they are compiled into a digitally signed report, and a written certification is available.
3. Checking a file later: Months or years later during discovery or trial preparation, anyone can independently verify the file. By running the video through any standard digital hashing tool, the newly generated hash should match the value we recorded. Matching hashes show the file is identical to the one we preserved.

SHA-256 is also collision resistant: no one has ever found two different files that produce the same hash, so matching values are strong evidence the file is unchanged. Admissibility is always decided by the court.

By integrating SHA-256 hashing into every in-person deposition we record, Akamai Legal Video provides attorneys with a verifiable record that helps answer claims of digital tampering.