Evidence rules (US and UK)

What a SHA-256 hash proves, and doesn’t, for message evidence

Last reviewed 2026-10-17 · 2 official sources cited below

A hash value is a short fingerprint calculated from a file’s exact contents. TextExhibits prints the SHA-256 hash of your export file on the cover page of every PDF.

What SHA-256 is

SHA-256 is one of the hash algorithms in the U.S. Secure Hash Standard, NIST FIPS 180-4. It turns any file into a 64-character hexadecimal string, like d11c6ad5…506a62. Change one character in the file and the hash changes completely.

How the federal rules describe hash values

The committee notes to Federal Rule of Evidence 902(14) explain:

“A hash value is a number that is often represented as a sequence of characters and is produced by an algorithm based upon the digital contents of a drive, medium, or file. If the hash values for the original and copy are different, then the copy is not identical to the original. If the hash values for the original and copy are the same, it is highly improbable that the original and copy are not identical.”

What a hash on your PDF shows

• That the transcript was made from one specific file: the export with that hash.
• That anyone with the same export file can recompute the hash and compare. If it matches, they have the identical file.
• With the paid hash certificate: the hash of every attachment, and a hash of the transcript text in the PDF.

What it does not show

• Who sent the messages, or that the conversation is genuine. A hash says nothing about how the export was created.
• That the export is complete. It covers whatever was in the file.
• Self-authentication by itself. FRE 902(14) requires a certification by a qualified person and notice to the adverse party. Software printing a hash is not that certification.

Verify a hash yourself

The output should match the cover page exactly (capitalization doesn’t matter).

Keep the file unchanged

Opening and re-saving an export in another program can change its bytes, and therefore its hash. Keep the original file in a safe place, and make copies of it rather than edited versions.

Sources

1. NIST FIPS 180-4 — Secure Hash Standard (SHS)
2. Federal Rules of Evidence, Rule 902 — Evidence That Is Self-Authenticating, incl. 902(13)–(14) and committee notes (Cornell LII)

Sources were opened and checked on 2026-10-17. Laws and rules change; always read the current version.