From: Petter Reinholdtsen <pere@hungry.com>
Date: Wed, 7 Jun 2017 19:36:06 +0000 (+0200)
Subject: New post on noark and trusted timestamps.
X-Git-Url: http://pere.pagekite.me/gitweb/homepage.git/commitdiff_plain/b7d321e91ae07ce1f58a34581206eb525d1b9878?ds=sidebyside

New post on noark and trusted timestamps.
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+Title: Idea for storing trusted timestamps in a Noark 5 archive
+Tags: english, offentlig innsyn, standard
+Date: 2017-06-07 21:40
+
+<p><em>This is a copy of
+<a href="https://lists.nuug.no/pipermail/nikita-noark/2017-June/000297.html">an
+email I posted to the nikita-noark mailing list</a>.  Please follow up
+there if you would like to discuss this topic.  The background is that
+we are making a free software archive system based on the Norwegian
+Noark 5 standard for government archives.</em></p>
+
+<p>I've been wondering a bit lately how trusted timestamps could be
+stored in Noark 5.
+<a href="https://en.wikipedia.org/wiki/Trusted_timestamping">Trusted
+timestamps</a> can be used to verify that some information
+(document/file/checksum/metadata) have not been changed since a
+specific time in the past.  This is useful to verify the integrity of
+the documents in the archive.</p>
+
+<p>Then it occured to me, perhaps the trusted timestamps could be
+stored as dokument variants (ie dokumentobjekt referered to from
+dokumentbeskrivelse) with the filename set to the hash it is
+stamping?</p>
+
+<p>Given a "dokumentbeskrivelse" with an associated "dokumentobjekt",
+a new dokumentobjekt is associated with "dokumentbeskrivelse" with the
+same attributes as the stamped dokumentobjekt except these
+attributes:</p>
+
+<ul>
+
+<li>format -> "RFC3161"
+<li>mimeType -> "application/timestamp-reply"
+<li>formatDetaljer -> "&lt;source URL for timestamp service&gt;"
+<li>filenavn -> "&lt;sjekksum&gt;.tsr"
+
+</ul>
+
+<p>This assume a service following
+<a href="https://tools.ietf.org/html/rfc3161">IETF RFC 3161</a> is
+used, which specifiy the given MIME type for replies and the .tsr file
+ending for the content of such trusted timestamp.  As far as I can
+tell from the Noark 5 specifications, it is OK to have several
+variants/renderings of a dokument attached to a given
+dokumentbeskrivelse objekt.  It might be stretching it a bit to make
+some of these variants represent crypto-signatures useful for
+verifying the document integrity instead of representing the dokument
+itself.</p>
+
+<p>Using the source of the service in formatDetaljer allow several
+timestamping services to be used.  This is useful to spread the risk
+of key compromise over several organisations.  It would only be a
+problem to trust the timestamps if all of the organisations are
+compromised.</p>
+
+<p>The following oneliner on Linux can be used to generate the tsr
+file.  $input is the path to the file to checksum, and $sha256 is the
+SHA-256 checksum of the file (ie the "<sjekksum>.tsr" value mentioned
+above).</p>
+
+<p><blockquote><pre>
+openssl ts -query -data "$inputfile" -cert -sha256 -no_nonce \
+  | curl -s -H "Content-Type: application/timestamp-query" \
+      --data-binary "@-" http://zeitstempel.dfn.de > $sha256.tsr
+</pre></blockquote></p>
+
+<p>To verify the timestamp, you first need to download the public key
+of the trusted timestamp service, for example using this command:</p>
+
+<p><blockquote><pre>
+wget -O ca-cert.txt \
+  https://pki.pca.dfn.de/global-services-ca/pub/cacert/chain.txt
+</pre></blockquote></p>
+
+<p>Note, the public key should be stored alongside the timestamps in
+the archive to make sure it is also available 100 years from now.  It
+is probably a good idea to standardise how and were to store such
+public keys, to make it easier to find for those trying to verify
+documents 100 or 1000 years from now. :)</p>
+
+<p>The verification itself is a simple openssl command:</p>
+
+<p><blockquote><pre>
+openssl ts -verify -data $inputfile -in $sha256.tsr \
+  -CAfile ca-cert.txt -text
+</pre></blockquote></p>
+
+<p>Is there any reason this approach would not work?  Is it somehow against
+the Noark 5 specification?</p>