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When a federated file is first accessed, a sha1 SHA-1 hash is computed and cached. This may take a while for large files. At any point, just like any other node, a request may be made through a web browser or client to recompute and compare the checksum of that file.
In the HTML view, beside the "digest" property for the content, there's a "check fixity" link which will recompute the sha1 SHA-1 and compare it with the last computed one. This feature is documented.
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- ensure that all files are visited/accessed to ensure a baseline sha1 SHA-1 is computed (will . This operation can take a very long time for larger large repositories).
- script a periodic fixity request against each object which looks for the SUCCESS assertion in the response.