The certificate that goes with the evidence ATTEST
Writes the certificate that turns files into evidence, in three of the forms usually asked for, hashes every file here in your browser, and refuses to produce a certificate with a hole in it.
What kind of certificate
What you did
The files it covers
Every file is read here to take its SHA-256. Nothing is uploaded, and the files themselves are not kept.
Drop the files here, or
Write it
The certificate
Show some lines, keep the rest back
Open a file that was sealed line by line and choose the lines to show. What you save holds those lines, where they are in the file, and the proof for each. No other line of the file is in it.
Check lines someone has shown you
Open the file of lines you were sent. Each line is checked here against the seal; nothing is sent anywhere, and checking costs nothing.
How it works
ATTEST writes the certificate that goes with electronic evidence, in three of the forms usually asked for, including a US Rule 902(14) certificate of authenticity. It hashes every file in your browser and lists each one with its fingerprint, so anyone can check the hashes later with standard tools and without this site. Privileged files can be excluded and recorded as such. No file is uploaded.
A text file such as a log can also be sealed line by line. Each line is hashed with its own salt into a Merkle tree, the tree Certificate Transparency uses (RFC 9162), and the certificate gives the tree’s seal. Later you can show a few lines, and whoever has the certificate can check that each is exactly that line of that file, without seeing any other line. The salt stops anyone confirming a guess at a line they were not shown. It proves where a line sat in the file that was sealed; it does not prove the file was complete when it was sealed, and it says nothing about the lines that are not shown. A sealed file of lines can be checked under Check lines someone has shown you, or by anyone following the method written into it.
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