What does a digest establish?
NIST's August 2015 Secure Hash Standard describes message digests as a way to detect changes since a digest was generated. Its publication page also records a plan to revise that standard. Use the project's approved current tool and algorithm; this worksheet is not a cryptographic implementation or a requirement to adopt a particular security system.
A digest comparison concerns the file bytes. It does not establish the identity of an untrusted sender, approval of a document, correctness of a reading or completion of a test. Commissioning Docs is independent and is not affiliated with NIST.
Which fields make a transfer discrepancy reviewable?
Create the manifest from the controlled original set, then retain that manifest in the authorized document system. Do not circulate confidential commissioning evidence publicly. A digest sent through the same untrusted channel as an altered file is not an independent trust anchor.
| Field | Sender record | Receiver check |
|---|---|---|
| Evidence identity | Test event and controlled document reference | Correct expected file, not merely a familiar filename |
| Revision | Issued document revision | Matches the intended transfer set |
| Original bytes | File size and approved digest algorithm | Same algorithm applied to the received bytes |
| Digest | Complete digest value | Compare the complete value, not an abbreviated display |
| Transfer | Package reference and authorized sender | Receipt identifies the same package |
| Discrepancy | Missing, extra or non-matching file | Preserve both records and obtain a controlled replacement |
| Acceptance | Commissioning review reference | Technical acceptance remains a separate decision |
What if the PDF looks the same but its digest changes?
Illustrative example. A fictional test package contains a signed PDF and a raw instrument export. The receiver prints and scans the PDF before saving it under the original filename. The scanned file looks like the expected document but no longer contains the same bytes. Its digest differs from the original manifest.
Keep the scan as a derived copy with its own reference. Request the original PDF through the authorized route, compare that file with the original manifest and record the receipt outcome. Do not edit the manifest to make an unexplained difference disappear. Re-saving a PDF or changing its metadata can change bytes even when the visible page appears unchanged.
How should missing and revised files be closed?
Reconcile expected entries, received entries and explanations before closing the transfer. A matching digest for one file cannot resolve another file that is absent. A legitimate revised document needs an explicitly revised manifest and approval reference, with the earlier issue retained.
The commissioning reviewer still checks the actual test evidence, conditions and criteria. This manifest neither certifies testing nor signs off engineering. Engineering sign-off is performed only by the registered engineer on the job.
Common questions
What else should the bid team know?
Does a matching digest prove a test passed?
No. It supports file integrity comparison, separate from technical acceptance.
Can a scanned replacement use the original digest?
No. Preserve the original and identify the scan as a derived file.
Should shortened digest strings be compared?
Retain and compare complete values using the approved algorithm.
Primary sources
- Secure Hash Standard, August 2015 publication and revision planning noteNational Institute of Standards and Technology