File Integrity Verification (Checksums)

Mnemonica protects your files with a checksum-based integrity check. The check shows that every copy of a file is byte-for-byte identical to the master on the platform. This article explains what a checksum is, how Mnemonica Gate verifies it automatically during transfers, and, in Archive Projects, where to find it in the Works.

What is a checksum?Copia il link alla sezione

A checksum (or digest) is a short fingerprint computed from the content of a file. If one byte changes, the checksum changes completely. When you compare the checksums of two copies, you know if they are identical or if one is corrupted.

Mnemonica uses three algorithms, depending on the context:

• SHA-256: the strongest, cryptographic fingerprint (64 hex characters). Use this value to verify the integrity of a file manually.
• xxHash64: a fast, non-cryptographic fingerprint. Mnemonica uses it for the quick checks during transfers.
• CRC32C: a lightweight checksum. Cloud storage uses it to detect transfer errors.

Automatic verification in Mnemonica GateCopia il link alla sezione

Mnemonica Gate version 3.4.0 or later checks every transfer it runs, both uploads and downloads. You do not need to switch anything on. The verification is automatic and built in.

The check has two parties. The Gate and the platform each compute the fingerprint of the same bytes independently. Then they compare the two fingerprints. Neither side trusts a number that the other side reports. The Gate computes the fingerprint while the file streams, so the overhead is minimal.

• Uploads: Mnemonica verifies them twice. It verifies block by block during the upload, to catch corruption early. Then it verifies the whole file at the end.
• Downloads: Mnemonica verifies the whole file at the end. Older legacy media has no reference fingerprint, so Mnemonica does not check it.

There is no "passed" badge. A successful check is silent: the transfer completes and the row clears from the queue. The Gate shows something only when a check fails. An upload that finished with no badge passed the verification. A clean download was verified, or it was a legacy file with nothing to check against.

If you pause and resume a transfer, you see the Resuming, verifying… indicator for a short time. The same happens when the Gate resumes a transfer after a network problem or an app restart. The Gate reads the transferred bytes again to continue the fingerprint from the right point. The progress bar is not frozen. You do not need to do anything.

When a file is flaggedCopia il link alla sezione

If the two fingerprints are different at the end of a transfer, the Gate flags the file. It shows an amber Integrity check failed label and an amber progress bar, on the queue card and on the file row.

The flag is advisory. The transfer completed and the bytes were delivered, but the copy does not match the master. Do not trust it. The Gate keeps the file in the queue so that you decide what to do. The Gate does not transfer the file again automatically.

What to do:

• Download: the downloaded copy can be damaged. Delete it and download it again.
• Upload: the copy that the platform received does not match your local file. Upload it again.

To see the two fingerprints side by side (local ≠ source), hover over the badge on the file row. If the problem comes back after repeated attempts, contact support. Send the file name and both digests.

Where to find checksums in the web appCopia il link alla sezione

In Archive Projects, you can also see the checksums stored for each file in the Works, in the Inspector panel.

The section shows one row for each available algorithm (SHA-256, xxHash64, CRC32C). The panel truncates the value to fit. To see the full fingerprint, hover over the value. To copy the full value to the clipboard, click the copy button.

Verifying a download manuallyCopia il link alla sezione

To confirm that a downloaded file matches the master on Mnemonica:

1. In the Inspector, copy the SHA-256 value of the file.
2. Compute the SHA-256 of your local copy:
   • macOS: shasum -a 256 <file>
   • Linux: sha256sum <file>
   • Windows (PowerShell): Get-FileHash <file> -Algorithm SHA256
3. Compare the two strings.

If the strings match exactly, the file is intact. If they are different, the download is corrupt or incomplete. Download the file again.