Privacy and security · Free practice
What a Document Hash Proves (and What It Does Not)
One useful skill to practice.
A fingerprint shows whether a file changed since it was generated. It does not show the contents are true. Here is the difference, and why it matters.
Read the full guide on CheckDispute Guides (opens a new tab)Check what you know.
3 questions. No sign-up. Your answers stay in this page.
A letter's fingerprint matches the one you were shown at approval. What does that establish?
Review all questions and explanations
- A letter's fingerprint matches the one you were shown at approval. What does that establish?
Answer: That the file has not changed since the fingerprint was generated
The Secure Hash Standard describes digests as used to detect whether messages have changed since generation. Detecting change is the entire claim.
- You re-save the PDF and the fingerprint is different. What does that mean?
Answer: The bytes changed, which is exactly what the property detects
Re-exporting, signing or flattening a form changes the bytes. A different value is evidence the file is not byte-identical, not evidence of wrongdoing.
- What actually decides whether a disputed entry is inaccurate?
Answer: The reinvestigation under 15 U.S.C. 1681i
A fingerprint identifies a file. The reinvestigation, generally within 30 days and extendable by up to 15 more, is what determines the outcome.
Your take-away checklist
- Save your own copy of every document at the moment you approve it.
- Record the fingerprint you were shown, next to the file it describes.
- Note the date and time of the approval.
- If you rebuild or correct the document, save the new version separately from the old one.
- Treat a signed copy as its own file; signing changes the bytes and the fingerprint.
- Before relying on a fingerprint, confirm you still hold the file it was computed from.
- Keep copies of anything you send, and send copies rather than originals.
Read the source, keep the context.
Original questions and worked examples from CheckDispute, checked against the full guide and primary sources below. Use the explanations to understand what each record does and does not establish.
- csrc.nist.gov: https://csrc.nist.gov/pubs/fips/180-4/upd1/final
- law.cornell.edu: https://www.law.cornell.edu/uscode/text/15/7001
- law.cornell.edu: https://www.law.cornell.edu/uscode/text/15/1681i
- consumerfinance.gov: https://www.consumerfinance.gov/ask-cfpb/how-do-i-dispute-an-error-on-my-credit-report-en-314/
- consumer.ftc.gov: https://consumer.ftc.gov/articles/disputing-errors-your-credit-reports
General education, not personalized legal advice. You can dispute errors directly for free. A practice score does not predict a credit or dispute result.